Electronics

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WHAT IS MATTER
(And why does it matter?)

Throughout mankind, we have tried to explain the things we see around us. This is probably what sets us apart from the apes more than anything else. While other animals are simply content with the fact that a rock is a rock and a tree is a tree, we as humans must investigate and find out WHY a tree grows, and HOW was this rock formed? At first, man broke things down into various groups. Along the way someone found they could be broken down into 3 groups: Animal, Vegetable, and Mineral. This worked fine for monkeys, which were animal, and trees which were vegetable. Rocks of course must be mineral. But what is coal? It used to be a vegetable until it was compressed over time. Now it is a mineral? Another way of classifying things was found: Solids, Liquids and Gases. This was clearly easy to define. All substances could be simply looked at, and determined whether it was a solid or not. Ice is a solid. Water is a liquid. Steam would be considered a gas. So what then is sunlight? What is magnetism? What is electricity? Benjamin Franklin concluded from his many experiments, that electricity had certain properties, such as pressure, current. He further concluded that it’s movement was predictable, like the pouring of water from one glass to another. From his conclusions, it was conventionally assumed that while we might not be able to SEE electricity at work, we could see it’s effects. And electricity, like unto water, acted like a fluid in every sense of the word. So again we pose the question, "What is MATTER?" And we answer the question as follows: Matter is the stuff around us.

Scientifically we define matter as all the "material" things about us. Matter includes all natural and man-made structures, liquids, metals, gases, etc.; in other words, everything that has weight and occupies space. All matter then takes up space. And anything that takes up space can be broken down into smaller pieces. A solid block of wood may be cut into smaller pieces until it is toothpicks, splinters, even sawdust. A gallon of water can be broken down into quarts, cups, even drops. But there comes a point where it can be broken down no longer and still retain it’s basic properties. In other words, there is a point where water can get no smaller, and still be water. That point is called the MOLECULE.

Atoms and the Definition of Electricity
We know that molecules exist, as some can be seen through an electron microscope. They look like clusters of yet smaller particles.But if the molecule is the smallest point that we can break our (example) water down to, and it still retain it’s basic properties (remain water), how can it have smaller particles? If we take water, and break it down through electrolysis, we find that water is made up of 2 chemicals or ELEMENTS : hydrogen and oxygen. Elements are arranged by their basic properties, as being metals, etc. on a chart known as the periodic table of the elements. When I went to school, all matter, regardless of size or state, could be broken down into approximately 105 different elements. Since then, more elements have been discovered, and will continue to be discovered. Some of the more common elements are carbon, copper, oxygen and aluminum. Elements may exist alone, or they may exist in clusters, or molecules, along with other elements. For example, a piece of copper wire is solely made up of the element copper. By comparison, water is a combination of two different elements: oxygen and hydrogen.

An element can be broken down into even smaller particles, called atoms. An atom is the smallest unit into which an element can be broken down and still retain its original characteristics. An atom resembles a little solar system. The center of this solar system, called the NUCLEUS , is made up of parts known as PROTONS and NEUTRONS . Around the NUCLEUS, tiny little particles are constantly rotating in an orbit. We call these particles ELECTRONS Fig. 1-1 illustrates and atom of helium. Note that it contains 2 electrons, 2 protons and 2 neutrons. The atom is far too small to be seen, even with the aid of the most powerful microscope. However, we do have a vast amount of knowledge about the atom and its inner parts. The proton differs both electrically and physically. Electrically, the proton is POSITIVELY CHARGED , and is about 1850 times heavier than the electron. The orbiting electron, on the other hand, is much lighter, and is said to be NEGATIVELY CHARGED . The neutron can effectively be thought of as consisting of both a proton and an electron. It has the same approximate weight as the proton, however, it is neutral in charge. This is because the positive charge of the proton cancels out the negative charge of the electron. Now atoms are not always so simple as the Helium atom discussed above. They always have the same parts, but not always in the same amounts or configurations. Atoms with more protons and electrons, of course, must be larger and heavier. Under normal circumstances, Atoms seek to be neutral in charge, and so will have an equal amount of electrons and protons. So if an atom like copper, has 29 protons in its center, it will also have 29 electrons. Because these electrons are rotating in an orbit, having too many electrons in a given orbit could cause them to crash into each other. So mother nature placed them in different orbits on different levels. We call them layers or rings. Depending on which ring we are discussing, each ring has a maximum amount of electrons which it can hold, without having to form another ring. For instance, the first ring can only hold 2 electrons. So if we

have an atom with 3 protons, (As in the case of Lithium) it must also have 3 electrons. Since it can only hold 2 electrons in the number 1 ring, it is forced to create a second ring, with only 1 electron in it. In the case of Lithium, this 1 electron is said to exist in the outer ring, or the VALENCE RING In Electronics, we are mainly concerned with this VALENCE RING, because it is here that the magic of Electronics takes place. If a given ring is shy of being full, it wants to “borrow” an electron from somewhere else. If an atom has one too many electrons, it pushes the “extra” electron way out on a ring of it’s own, and tries to “loan” it to another atom. Electronics, in its purest form, is the study of the movement of electrons from one atom to another. Usually, this takes place by borrowing and loaning (temporarily) of electrons. While we can not actually see this going on, we can monitor it’s effects, which can be amazing!

The Law of Electromagnetic charges:
Most objects, such as a piece of cork normally have a neutral or zero charge; that is, they contain as many electrons as they do protons. If a piece of cork could be made to have an excess of electrons, it would become negatively charged. On the other hand, if the cork were to be made to have a deficiency of electrons, then we would have an excess of protons, and it would then be positively charged. If we take any positively charged body, and bring it near a negatively charged body, the two bodies will be drawn together. If on the other hand, the two objects have like charges, then they will repel each other. These two reactions form the basis of the first law of electricity, known as The Law of Electromagnetic Charges. The law states: Like charges repel, and unlike charges attract.

Differences of Potential:
If we connect a copper wire between two oppositely charged bodies, an electron flow would result. Electrons will flow from the negatively charged

body to the positively charged body. This is because it is a basic law of nature that CHARGED BODIES SEEK TO BECOME NEUTRAL . What happens here, is that the positively charged body,which has a deficiency of electrons, attracts the excess of electrons from the negatively charged body. This action continues until the deficiency and excess of electrons disappeared and the two bodies become neutral. Any difference in charge between two objects will result in the development of a DIFFERENCE OF POTENTIAL between them. We call this difference of potential ELECTRICAL PRESSURE , or VOLTAGE .

Conductors, Insulators, and Resistors.
Conductors and Insulators
Because of the distribution of electrons in the VALENCE RING of a natom, some elements will allow electrical current to flow easier than others. Materials which easily allow the flow of electric current are called CONDUCTORS . CONDUCTORS do not hold tightly to the electrons in their VALENCE RING, and are said to have a large number of FREE ELECTRONS . Some examples of good conductors are Gold, Silver, Copper, Aluminum, Zinc, and Carbon. Other elements do not allow electrical current to flow easily, and these are called INSULATORS . INSULATORS tend to hold tightly to the electrons in their VALENCE RING, and do not want to share with other atoms. Some examples of good insulators are Quartz, Mica,Teflon, Polystyrene, and Water. (Yes, water is an insulator.... not a conductor. This will be explained later in more detail).

Resistors and Resistance:

If water is moving through a hose, we say that it has FLOW . If we restrict the flow, by pinching the hose, we are causing friction at the point of restriction. This friction can be said, is resistance to the flow of the water. Electricity, according to Benjamin Franklin, acts like a fluid. It flows and has a measurable CURRENT . We can restrict its flow by adding electrical friction. We say that the restriction of electrical flow is called RESISTANCE and that a device which causes such RESISTANCE is called a RESISTOR . All materials, even the very best CONDUCTORS demonstrate a certain amount of RESISTANCE to electron flow. In order to compare the resistance of various materials, we need to have some standard unit of measurement. The unit of measurement for resistance is called the Ohm , and is indicated by the Greek letter Omega ( Ω ). One Ω is defined as the amount of resistance that a 1000 foot piece of #10 copper wire has. A 3000 foot piece of #10 copper wire would have 3 Ohms of resistance. A 500 foot piece of #10 copper wire would exhibit 1/2 an Ohm, etc. Although Ohm is the basic unit, KiloOhm and MegOhm are frequently used. 1 KiloOhm (K Ω) is equal to 1 thousand Ω. 1 MegOhm (M &Omega) is equal to 1 million Ω. There are 4 factors that determine the resistance of a material: (1) Type of Material The resistance of various types of materials are different. For instance, gold is a better conductor of electricity than copper, and therefore has less resistance. (2) Length The resistance of a material is directly proportional to it's length. The longer the material is, the more resistance it has. This is because the electrons must flow through more

material, and therefore meets more friction over the entire distance. (3) Cross Sectional Area The resistance of a material is inversely proportional to the cross sectional area of the material. This means that the thicker the substance is across, the lower the resistance. This is because the larger the cross sectional area is, the less friction there is over a given length. (Picture in your mind, if you will, that a fire hose will pass more water than a garden hose, because the wider the pipe, the less resistance it has). (4) Temperature In various types of materials, resistance can vary inversely or directly with the temperature. This is because of the chemical properties of the material. In Carbon, for instance, the resistance decreases as the temperature rises. So we say it varies inversely. In copper, however, the opposite is true, with the rise in temperature, we have a rise in the resistance. Resistance then, is basically a form of friction which restricts the flow of an electrical current. In basic science class, you learned that by putting your hands together, and rubbing them quickly, your hands get warm. This is because friction generates heat. Electrical friction - RESISTANCE - also generates heat. So not only can resistance change with heat, but causes heat as well. An important point to remember when working with resistors, especially in high power circuits.

Voltage and Current

Already we have touched on the two terms VOLTAGE and CURRENT . Now it is time to discuss them further. VOLTAGE is the term used to describe the electrical "pressure" or difference of potential that we spoke of earlier. Just as water pressure is the force in physics that pushes water through a pipe, VOLTAGE is the physical force which pushes electrons through a wire. Examine illustration 4.1. You see a large tank with a hose attached to the bottom of the tank. When the tank is full of water, gravity causes that water to exert pressure, which pushes down toward the bottom of the tank. With the hose at the bottom, it allows a place for the water to escape. Water Pressure, therefore causes water current to flow through the hose.

In the same sense, electrical pressure - just as water pressure pushes water through a pipe. Voltage , causes CURRENT to flow through a wire. VOLTAGE has several other names. It is sometimes called ELECTROMOTIVE FORCE (E.M.F. for short), IR DROP (this will be explained a little later), and POTENTIAL DIFFERENCE . The unit of measurement for VOLTAGE is the VOLT , and it is measured by a VOLTMETER . You may run into KiloVolt s (Thousand Volts), MilliVolt s (1 Thousandth of a Volt), or even MicroVolt s (1 Millionth of a Volt). The problem with discussing VOLTAGE is that it is difficult to talk about it, without discussing CURRENT and RESISTANCE in the same breath. The three are almost inseparable, as you will soon come to see. CURRENT is the term used to describe the FLOW or movement of electrons. The principle shouldn't be foreign to you by now. Water has current. Electricity has current. Water has current only when the river flows. If it is standing water, such as in a pond, it does not flow, and therefore has no

current. Electricity only has current when it is on the move. Current is measured in AMPERE s, using an AMMETER , typically discussed as MilliAmpere ( 1 thousandth of an Ampere ) s or MicroAmpere ( 1 millionth of an Ampere ) s. Quite often, for the sake of quick speach and quicker typing, it is shortened to just 'Amps or MilliAmps.

Sources of Electricity
Although electricity is a naturally occurring phenomena, in its natural forms, (Lightening, Static Electricity, etc) it has bee of little use to mankind. We have, however, invented ways to generate electricity. Electricity can be generated by Chemical, Magnetic, or Transducer methods. Chemical :The earliest records of Electronics finds the early Egyptians having discovered how to make a crude battery, using lemons (which have citric acid) and two dissimilar metals. Batteries to this day are still produced using two dissimilar conductive materials into an acid ELECTROLYTE . Modern batteries are a little more complex than a couple of batteries though: Perhaps the most common battery in use today is the dry cell, which can be found in nearly every flashlight! The dry cell contains a carbon rod, which acts as the positive terminal, surrounded by a core consisting of manganese dioxide, zinc chloride, glycerin, carbon particles, and sawdust. Around this core is a chemical paste made up of an ammonium chloride solution in starch. A zinc can is then used as the container for the cell and also acts as the negative terminal.

The carbon rod reacts with the zinc casing via the pasty electrolyte. This creates a 1.5 Volt potential difference between the positive and negative terminals of the cell. It is not the electrolyte, but the electrodes themselves (the zinc and carbon) which determine the voltage of the cell. Therefore, no matter which electrolyte is chosen to be placed between the zinc and the carbon, the cell will still produce 1.5 Volts. So how do we come up with a 9 Volt battery? Simple. By placing cells in series, we can add the Voltages together. Two 1.5 Volt cells in series would produce a 3 Volt output. 3 would product 4.5 Volts. 6 would produce 9 Volts. When we place cells in series, we say that it is a BATTERY of cells. A close cousin to the Egyptian batteries is the modern LEAD-ACID type battery. Commonly used as automotive type batteries, the negative electrode is made up of pure lead and the positive electrode is a leadperoxide combination.The electrolyte nominally used is a diluted sulfuric acid. A single lead-acid cell produces 2.1 Volts, but these batteries are commonly produced in either 6.3 or 12.6 Volts.

Direct Current Theory
If we take a light bulb and connect it to a battery, the bulb will light up. The lamp lights up because current flows through it. The current leaves the battery at the negative terminal, flows through the bulb, and returns to the positive terminal of the battery. The electrons flow in one direction. This is known in electronics as DIRECT CURRENT flow because the electrons flow only in one direction. The arrows in the figure show the direction that the current would flow in this circuit. As long as we can follow the current from the negative terminal of the battery throughout the entire circuit, and back to the positive terminal, we have a COMPLETE CIRCUIT PATH . It is very

important to remember that current will ONLY flow if the circuit path is complete. If we were to remove the light bulb from the circuit, the circuit path would not be complete, and while voltage would still exist on the battery, no current would flow through the circuit. In order to have any complete circuit, you are required to have at least 3 parts: (1) The SOURCE or SUPPLY of Voltage. (2) The LOAD which uses the source Voltage. (3) A complete path of connecting wires.

Schematic Symbols
Sometime over the years, some bright soul determined that it would be difficult to draw a picture of every component that you decided to put into a circuit. However, they needed a way to tell their colleagues about discoveries and accomplishments. So a system was developed that was a sort of "electrical shorthand". They call it a SCHEMATIC DIAGRAM and the individual component representations are called SCHEMATIC SYMBOLS . Throughout the course, I will be introducing you to the various SCHEMATIC SYMBOLS one by one. This lesson will take you through the first two symbols, and describe how they are used in a circuit. The first three SCHEMATIC SYMBOLS you will be introduced to are the lamp, battery and resistor. Remember that a resistor is any device which causes electrical friction. In electronics, the resistor can be substituted for any current load. The schematic symbol for a battery can likewise be substituted for any direct current supply voltage. So, in essence, we could theoretically use our battery and resistor to represent our light bulb circuit. You will notice that the picture on the left is the same one we just looked at. The one on the right actually has two schematic diagrams. The schematic on the left is an exact representation of the picture on the left. The schematic on the right we say is an ELECTRICAL EQUIVILANT circuit for the one on the left. Any circuit, no matter how complex, can be broken down to being a source and a

load. The resistor represents the light bulb, which is the load of the circuit. Anytime you are having a problem figuring out how a circuit works, it can be helpful to break it down to an ELECTRICAL EQUIVILANT circuit. The SCHEMATIC SYMBOL for the light bulb is pretty self explanatory. The Schematic for the resistor looks like a series of sharp turns. Just remember that on a road, you have to slow down at sharp turns, and electrical flow (current) has to slow down at a resistor. The battery needs a little explanation. The lines represent the electrodes of a battery. Note that the SHORT line is always the NEGATIVE terminal, and the longer line is always the POSITIVE terminal. Also along the way, I will try to give you an idea of what certain types of electronic components look like, although there are so many shapes out there, I can not possibly cover them all. I am fairly certain you already know what a battery and a light bulb look like, but you may never have seen a resistor. There are many types of resistors, but some of the most common types are shown in the picture to the left. The top one is a ceramic coated " wirewound ", which, as its name implies, consists of a winding of wire, cut to a certain length to create a certain amount of resistance. The second is a carbon composite, and the third is a metal film or metal oxide, which has very tight resistance tolerances. Note that on wirewound resistors, the values are printed on the side, whereas the carbon and metal types have their values painted on as color coded bands around the resistor.

EXTRA CREDIT
Not a required part iof the course, but if you wish to pursue electronics, you should probably memorize the resistor color code. It will be used throughout your career.

THE RESISTOR COLOR CODE
Many resistors that are produced are very small. In addition, resistors can get extremely hot with use. So hot, in fact, that they will often burn off any small lettering that may be printed on them. For this reason, resistors have been made with colored bands painted onto them. These bands conform to a universal color code, which identifies the value and tolerance of the resistor. Each of the colors below, correspond to a particular number.

For the purpose of memorization, I was taught a MNEMONIC to remember the colors and their related numbers. However, for reasons of political correctness, I can not teach you the same mnemonic. The mnemonic procedure, though, is still valid, so I will present you with a new - more politically correct one. If you memorize this phrase, you will never forget the resistor color code: Black Bunnies Run Over Your Greens But People Get Wise - Ripe Golden Squash Now If you remember this mnemonic, you will not only know the values of resistors on sight, but also their tolerances. Here's how it works: Using the above phrase, it will indicate the following numbers:
BLACK BROWN 0 1 RED 2 ORANGE YELLOW GREEN 3 4 5 BLUE 6 PURPLE GREY 7 8 WHITE 9

Resistors may have anywhere from 3 to 6 colored bands on them. As a rule, the first two bands are the "value bands", so the color directly corresponds to the value. In the example, we are using a 27,000 Ohm ( or 27K Ohm ) resistor. The first two colors are RED and PURPLE, indicating the numbers 2 and 7. This is where things get tricky. On the 3 an 4 band resistors, the third band, called the "MULTIPLIER" - in this case being Orange, indicates that the 27 is followed by THREE zeros ( 000 ). So in this case, we have 27 followed by 000 or a 27,000 Ohm resistor. If there are only 3 bands, then we are done. 2 Questions arise though: 1. Why did we memorize the "Ripe Golden Squash Now" portion of the mnemonic? We already have all 10 numbers! 2. What about the 4th band?

Very good questions. They are both answered at the same time. The "Ripe Golden Squash Now" portion of the mnemonic refers to the 4th band, which is known as the "TOLERANCE" band. It has a very important job. (Note that the LAST band is ALWAYS the Tolerance Band. It usually has a wider separation than the other bands have from each other ( it is farther away ). We as people, are not perfect. Because of this, we make imperfect products. No resister is perfect. They are, however, all close to the value listed on them, plus or minus a certain amount. The amount of difference between their actual value, and the value listed on them should always fall within a certain tolerance. That tolerance is listed on the resistor, and is also designated by a colored band. Ripe Golden Squash Now (RGSN) corresponds with Red, Gold, Silver, None - the order of resistor tolerances in ascending order. Red = 2%, Gold=5%, Silver=10%, and No Band (None) = 20%. Let's assume that you have a 1000 Ohm resistor. If it has a 10% tolerance, it can be off by 100 Ohms, and still be good (1000Ω +/- 100Ω). So it will be allowed to be anywhere from 1100 to 900 Ohms, and

still be considered good. If a 1000 Ohm resistor has a SILVER tolerance band, and is only 920 Ohms, it is considered to be within tolerance, and is a good resistor. However, if a 1000 Ohm resistor has a GOLD or RED tolerance band, and is only 920 Ohms, it is OUT of acceptable tolerance, and is considered to be a bad resistor. Now in the second example, we also have a 27,000 Ohm resistor, but the color code scheme is a little different. We still have a RED and a PURPLE as our first two colors, indicating the number 27, but the third band, instead of being orange, is BLACK, indicating Zero. The FOURTH band is the multiplier, and being RED indicates 2 zeros. Here is how this resistor is read: 27 0 00, or 27,000.

Ohm's Law
Thus far, we have discussed current, resistance, and voltage. Now we shall discuss the important relationship that exists between the three. Around 1840, German physicist Georg Ohm noted that there was a distinct mathematical relationship between Voltage, current and resistance. He then wrote the basis for what we now call OHMS LAW . Ohm's Law states that Voltage (in Volts) is equal to the product of the current flowing through a resistance within a circuit. In other words... Voltage = Current times Resistance. Now comes the bone in the throat of the student. While we measure Voltage in Volts, we often use the letter E to represent Voltage. This is because another word for Voltage is ELECTROMOTIVE FORCE, which is shortened to EMF or simply E. Also, we use the letter I to represent current. So that our formula becomes:

So what does this mean? Simply put, if we have a resistance of 10 Ohms (R=10), and a current of 10 Amps(I=10), we will have a Voltage of 100 Volts, because 10*10=100 (E=100). Ohms law can also be stated two other ways. By using basic algebra, we can turn the formula around to make it say:

and EXTRA CREDIT: Learning about Ohm's Law is fine and dandy, but if you are going to USE Ohm's law on a regular basis, you really ought to memorize it. Memorizing Ohm's law may sound like a time consuming and daunting task, but if you do it the Electronics Theory.Com way - you'll have it committed to memory for life within a few minutes! You just have to imprint a picture in your mind. Years ago, Native American Indians used to roam the plains of the United States. These Indians would look across the plains, and see all kinds of animals. They would see rabbits running across the field, and eagles soaring in the sky. Now, picture things from the Indian's stand point - he sees the Eagle flying over the Rabbit: Say to yourself Indian equals Eagle over Rabbit. Now just use the first letter of each word: I = E over R, which is this formula:

However, from the Rabbit's point of view, he sees things a little differently. The Rabbit looks out and sees the Eagle flying over the Indian. Say to yourself Rabbit equals Eagle over Indian. Now just use the first letter of each word: R = E over I, which is this formula:

Finally, the Eagle up in the sky sees both the Indian and the Rabbit standing on the ground together. Say to yourself Eagle equals Indian and Rabbit together. Now just use the first letter of each word: E = IR, which is this formula:

Now if you simply remember the story of the Indian, Eagle and Rabbit, you will have memorized all three formulae.

Ohm's Law Continued

So now we have 3 different ways that we can algebraically express Ohm's Law.

or

or

But of what significance is it? Here is the gist of it. If we know 2 out of the 3 factors of the equation, we can figure out the third. Let's say we know we

have a 3 Volt battery. We also know we are going to put a 100 Ω resistor in circuit with it. How much current can we expect will flow through the circuit? Without Ohm's Law, we would be at a loss. But because we have Ohm's Law, we can calculate the unknown current, based upon the Voltage and Resistance.

Let's try another problem. Say we have the circuit below. We know the Voltage and the Current, because we have meters to indicate such in the circuit. When we plug in the unknown load resistance, the Voltmeter reads 45V and the Ammeter reads 2 Amperes. What is the resistance of the load? Well now, if'n I done my math a'right, I should be using this formula:

Series Resistance
Ohm's Law teaches us that Voltage is equal to the product of resistance and current. This is fine if we have a circuit as simple as a single light run

by a battery. But how often do we truly encounter a circuit which has only one resistance? It is actually quite seldom. Most circuits have many resistances in various combinations. So we must learn how to mathematically deal with all these resistances. Fortunately, combined resistances can only be configured in two ways: Resistances Combined in Series Resistances Combined in Parallel We will discuss each of these separately. This class is dedicated to the study of Resistances in Series, which you will find, are as simple as 2+2. First, let us describe the difference between a SERIES circuit and a PARALLEL circuit. A SERIES circuit is hooked together like a chain, with each link connected to the link before it. If any given link in the chain is broken, the whole chain is broken, and doesn't work. If we think of our circuit as a water pipe, a resistor could be a valve in the pipe. A series circuit would have several valves in the same pipe. If we shut the water off at any one valve, the water flow through the entire pipe would be restricted. Let's say this again another way. The flow, or current, is restricted by all the valves, but the valve with the most resistance is the one that decreases the flow the most. Now if we draw a schematic of resistors in series, it would look like the diagram at the left. This first diagram would be an exact representation of our waterflow circuit. The tank provides a source of water, just as a battery supplies a source of electricity. The valves, which restrict the flow of water, represent the resistors, which restrict the flow of electric current. The diagram on the right shows the equivalent circuit, with only one resistor (Rt) taking the place of all 3 resistors in the left diagram. Recall that using an electrical equivalent circuit, that ANY circuit, no matter how complex, can be represented with a single voltage source, and a single load. The question is, how do we determine the value of the TOTAL resistance when we have multiple resistors? This is the scope of this lesson. How do we mathematically combine resistances that are connected in series? As I said before... it's as easy as 2+2. If two or more resistors are connected

end to end, as in a chain, we say that they are in series. To find out the TOTAL RESISTANCE of resistors in series, all we have to do is add up their individual values. It's that simple. If we have 3 resistors, (R1, R2, and R3) each with a value of 2 Ω, the total resistance (RT) of the series circuit would be 2+2+2, or a total of 6 Ω. Hence, RT=R1+R2+R3+... is the formula for resistors combined in series.

Series Resistance and Ohm's Law
So far, we have learned that if two or more resistors are connected end to end, they are in a SERIES circuit. We learned that the total resistance in a series circuit is equal to the sum of the individual resistances. What we didn't discuss, so far, was the relationship between Voltage, Current, and Resistance in a circuit with multiple resistances. If we examine our waterflow circuit, we find that any water which flows past the 3rd valve, must first flow past the 2nd and 1st valves. By this we can deduce that the current, or flow of water, is the same past all three valves. At no time can more water flow past one valve than past another. The same is true in electronics. In a SERIES circuit, the current is the same at every point.

Using our previous example of 2 Ω resistors, if we then have a 12 Volt source, what would be our current through the circuit? Let us examine this. We know that because the circuit is series, no matter where in the circuit we are, the current will remain the same. So the problem is, what would be the given current for the complete circuits given voltage and resistance totals? Adding up our 3 resistors, we come to 6 Ω , and we know

our Voltage is 12. So using Ohms Law, we derive this formula:

Parallel Circuits

We mentioned prior, that there were 2 types of circuits, SERIES and PARALLEL. So far, all we have talked about is series. Now we are going to discuss the difference between a series and a PARALLEL circuit. In the series circuit, all the electricity followed the same path. In our waterflow representation, this meant that all the water flowed through 1 pipe. In PARALLEL circuit, however, there are multiple paths that current can flow through. Notice that in the picture to the left, that there are 3 different paths which the water can take. All 3 paths have the same incoming pressure, but the flow of some paths can be more restricted than in others. Parallel circuits in electronics work on the same principle. While there may be multiple paths for the electricity to flow through, the electrical pressure (Voltage) remains the same through all paths. As you can see from the diagram on the right, there are 4 meters placed in this circuit to measure the current. The first 3, (A 1 , A 2 , and A 3 ) measure only the current flowing through that individual leg of the circuit. The 4th, A T measures the Total current of the circuit. If you take the three individual currents, and add them all together, they will equal the total current, measured on the 4th meter. From this we can see that the current in a parallel circuit is additive.

Resistance in a parallel circuit can be quite a bit trickier than in a series circuit. It is found by " Reciprocating the Sum of the Reciprocals ". (huh?)Simple. Taking the reciprocal of a number means dividing "1" by that number. The reciprocal of 2 would be 1 divided by 2 or ½. Most modern calculators have a [1/X] button just for this purpose. So if you take the reciprocals of the values of all of the resistors, which would, of course, give you a bunch of fractions, and add them all up, then reciprocate their sum, you would have the answer. The formula would look something like this:

Parallel Circuits - the Plague!
Now that I have you thoroughly confused, let me make things as clear as mud for you.Let's begin with a very simple circuit: 2 resistors and 1 battery. You are given the following information about the circuit: R 1 = 50 Ω R 2 = 200 Ω A 1 reads .2 Amps in current ( I=.2 ) Find: Total Voltage Total Circuit Resistance Total Current And Finally, the Current through A 2 Now this isn't as tuff as it first looks. Let's break the problem down. We know according to Ohm's law, that if we know the resistance and current, we can find the voltage. E R1 = I R1 x R 1 . E = .2 x 50 = 10 E = 10 Volts. Now that we know that the voltage for the entire circuit is 10 volts, let's find the total Resistance. First, we find the reciprocals of the individual resistances: R 1 = 50 ohms. 1/50 = .02 R 2 = 200 ohms. 1/200 = .005 Now we add the two reciprocals together: .02 + .005 = .025 Finally we take the reciprocal of the sum:

1 / .025 = 40 Ω So if the Total Voltage of the circuit is 10 Volts, and the Total Resistance = 40 Ω then by using Ohms Law again we can find the total current. I Total = E Total / R Total I = 10/40 = ¼ Ampere. Almost finished now. So far we know: R 1 = 50 Ω R 2 = 200 Ω A 1 reads .2 Amps in current ( I=.2 ) V Total = 10 R Total = 40 and I Total = ¼ Now we have at least 2 methods by which we can find the current through A 2 . We know that the Total current is the sum of all the individual leg currents, so if we subtract the current of A 1 from the Total current we get this: I Total - I 1 = I 2 .25 - .2 = I 2 = .05 Amperes. The other method would be by using Ohms Law. We know the resistance of R 2 = 200 Ω. We also know that the voltage across R 2 = 10 Volts. Hence: 10 Volts / 200 Ω = .05 Amperes. Either way, our final result is A 2 = .05 Amps

Series and Parallel Resistances - a Summary
To summarize all that we have just learned:


There are 2 types of circuits.... Series and Parallel. o Series Circuits  Are connected in a straight line, like a chain.  All current remains the same throughout the circuit.

I Total = I 1 =I 2 =I 3 etc...
 

There can be many different voltages in a series circuit, as a voltage drop appears across every resistor. The total voltage in a series circuit is equal to the sum of all the individual voltage drops within the circuit. E Total = E 1 + E 2 + E 3 + etc...

 

The total resistance in a series circuit is equal to the sum of all the individual resistances within the circuit. The formula for Resistance in Series is: R Total = R 1 + R 2 + R 3 + etc...

o

Parallel Circuits  Are connected allowing multiple paths for current flow.  All voltage remains the same throughout the circuit. E Total = E 1 =E 2 =E 3 etc...


 

There can be many different currents in a parallel circuit, as each leg has the same voltage, but can have a different resistance. The total current in a parallel circuit is equal to the sum of all the individual currents on each leg of the circuit. The formula for Current in Parallel is: I RTotal = I R1 + I R2 + I R3 + etc...

 

Resistance is found by reciprocating the sum of the reciprocals of the resistance of the individual branches The formula for Resistance in Parallel is: 1 ----------------------------------1 1 1 1 1 ---- + ---- + ---- + ---- + ---- + R 1 R 2 R 3 R 4 R X...

o

Ohm's Law states that there is a relationship which exists between current, resistance, and voltage, such that E = I x R

Series - Parallel Resistances the Combination
Whenever we work with circuits in the real world, they are seldom as straightforward as a simple series or parallel circuit. Normally, they are a combination of the two, called a SERIES-PARALLEL circuit. While they look forbidding at first, you must keep in mind that ALL circuits can be broken down into smaller parts. They can be made simpler to work with. Such is the case with the Series-Parallel circuit. If you look at the example on the right, it has 3 resistors and 1 battery. R 1 and R 2 are both 10 Ω in parallel. 1 -----------1 1 ---- + ---R1 R2 If we do the math (reciprocating the reciprocals), we come up with a total of 5Ω for these two. We can say that: R 1&2 = 5Ω. We also have R 3 in the circuit, which is 20Ω. Once we have combined the 2 parallel resistors, we have a simpler circuit.... 2 series resistors. R 1&2 and R 3 . If we add the value of these two resistors, we come up with R Total =R 1&2 +R 3 . So R Total =5Ω+20Ω=25Ω. Then if we know the voltage, we can find the current through the entire circuit, and through each individual resistor. Go ahead and try plugging in a voltage (like 25V) and finding the currents. You'll be surprised at how simple it is. Let's try another example. In the circuit on the right, we have 3 resistors again. But this time, they are configured differently. Do you see how you would combine them for the

total resistance? First, you must add the 10 Ω resistors by adding them. This is simple because they are in Series. 10 Ω + 10 Ω = 20 Ω. Using our parallel circuit formula then: 1 -----------1 1 ---- + ---R1 R2 We find that our total resistance for the circuit = 10Ω. Note that if we have the same battery (25V), our current turns out much different through the entire circuit. So the same components, configured differently, will create a vast difference in the way the circuit works.

Pure Unadulterated Power

Power is defined as the rate of which an amount of energy is used to accomplish work. In the mechanical realm, we tend to use the term "horsepower" when describing how much energy a engine can develop. In electronics, we use the term WATT when describing the amount of power used by something. As discussed in a previous class, whenever a given current flows through a wire or device, it causes a form of electrical friction. We call this friction

RESISTANCE. This friction is caused by the moving of electrons through and between molecules within the resistor. This friction causes 2 other effects: Heat and Noise. The noise is called Johnson noise, and for now, we will ignore this effect, as it is very negligible. The speed, or rate at which the heat is generated defines the power that the resistor consumes. This power consumption represents a loss, because we do not make use of the heat that is dissipated. It becomes important to know how much power a resistor is dissipating, because it will burn up if it can not withstand the heat. For this reason, resistors have both a resistance rating in Ohms, and a power rating in Watts. A resistor which is rated at 2 watts can safely dissipate 2 watts. If a 2 watt resistor is forced to dissipate 5 watts, it will burn up, and its resistance value will change accordingly. The question then arises, "How do we calculate the amount of power dissipated by a resistor?" I Thought you'd never ask! The formula for power is not unlike Ohm's Law. As a matter of fact, it is called Ohm's Watts Law. And remembering the formula for Power is a piece of pie! (Don't I mean a piece of cake?) Nope.... PIE! You see, Power (P) is equal to the product of the Current (I), and the Voltage (E) in a given circuit.

Of course, using algebra, you can derive 2 other formula's from this one.

and

Electromagnets
We defined POWER as the RATE of doing work. The actual work or capacity to do work is called ENERGY . Energy can be Kinetic (dynamic), Potential (static), or Radiant (electromagnetic) in nature. Energy, according physical law of "Conservation of Energy", is never lost nor gained. It may be changed from one form to another, but it never just "dissapears". Just like in our resistor, we had energy being used which was dissipated as heat. The electrical energy was transformed into heat energy. It didn't dissappear, it merely changed form. There are many other forms of energy. Some other forms of energy are light, sound, momentum, and MAGNETISM . We are all familiar with magnets, and their peculiar properties which make them seem almost magical. A magnet can be used to hold a screw onto a screwdriver, to lift a car, or find your way in the forest. But what is it that makes a magnet do what it does? If we take a magnet, and mark one end of it, we can identify one end from the other. If we then suspend the magnet from a string, so that it is free to rotate, we will notice that one end will ALWAYS point toward the north, and that it will ALWAYS be the same end of the magnet that points north.

From this, we have concluded that there is a NORTH POLE and a SOUTH POLE on every magnet. Typically the north pole is marked with an N, and south pole is marked with an S. Now if we take two magnets with known, marked poles, and bring the North Pole of one magnet close to the South Pole of the second magnet, the two magnets will PULL TOWARD one another until they are connected. If we reverse the experiment, and bring the North Pole of one magnet, near the North Pole of the second magnet, they will PUSH AWAY from each other. This effect is called the LAW OF POLES which states: OPPOSITE POLES ATTRACT each other, whereas LIKE POLES REPEL each other. Why is it that magnets act this way? And why do magnets have poles? These are questions which science has found difficult to answer. It is believed, though, that according to the Molecular Theory of Magnetism inside of all magnets, the tiny molecules that the magnet are made of, are all little tiny magnets in themselves, and that they are all lined up in a row. In a normal piece of steel, for instance, the molecules are arranged in random order, with positive and negative poles scattered about in all directions. But when magnetized, the tiny magnetic molecules line up, allowing the whole piece of steel to act like one big magnet. If we place a magnet beneath a piece of paper, and place iron filings on top of the piece of paper, the result would look something like the example to the right.

The iron filings will arrange themselves to LOOK like the invisible magnetic force which surrounds the magnet. This invisible magnetic force which exists in the air or space around the magnet, is known as a MAGNETIC FIELD , and the lines are called MAGNETIC LINES OF FORCE . Now if we take a non-magnetic object, such as a glass rod, and place it within the path of a magnetic field, the lines of force produced by the field would pass right through the object. If, however, we wrap a magnetically conductive layer around the object, such as a soft iron, the iron will cause the lines of force to bend, and go around the object instead of through it. This is called a SHIELDING effect.

Electromagnets
There are actually 2 types of magnetism: 1.) Temporary 2.) Permanent Soft iron can be easily magnetized by placing it inside a magnetic field. However, as soon as the iron is removed from the field, most of its magnetism fades away. A negligible amount of magnetism is, however, retained. This type of magnet is called a TEMPORARY MAGNET . The small amount of magnetism that does remain is called RESIDUAL MAGNETISM . Steel or hard iron, which is difficult to magnetize, retains the majority of its magnetism long after it has been removed from the magnetic field. This type of magnet is called a PERMANENT MAGNET . Permanent magnets are generally made in the shape of a bar or a horseshoe. Of the two shapes, the horseshoe type has the stronger magnetic field because the magnetic poles are closer to each other. Horseshoe magnets are used in the construction of headphones. Loudspeakers, on the other hand, generally use a type of Bar magnet.

It has been found that when a compass is placed in close proximity to a wire, and an electrical current flows through the wire, the compass needle will turn until it is at a right angle to the conductor. Since a compass needle lines up in the direction of a magnetic field, there must be a magnetic field around the wire, which is at right angles with the conductor! Science has discovered then, that wires which carry current have the same type of magnetic field that exists around a magnet! We say that an electric current INDUCES a magnetic field. If you closely examine the picture on the right, you will find that there are "rings" circling about the wire. These rings represent the magnetic lines of force which exist around a wire which carries an electric current. They are strongest directly around the wire, and extend outward from the wire, gradually decreasing in intensity. You will also note that the compass needle is steady, and not spinning. This indicates that the magnetic field goes in a ring around the wire. It also travels in a specific direction. The direction of the magnetic field can be predicted by use of what we call the LEFT HAND RULE . According to the left hand rule, if you wrap your left hand around the wire that is carrying the current, with your thumb following the direction of current flow (thumb points positive), your fingers will show you what direction the magnetic field will turn. Note that when the current flows from negative to positive, it induces a magnetic field in a specific direction, such that the north pole is ALWAYS at right angles with the electrical current flow.

No matter which way we turn or twist the wire, the left hand rule applies. But what happens if we put a loop in the wire? When the wire is looped, as you will see from the picture on the right, the little magnetic fields that wrap around the wire cross through each other's path. If you use the left hand rule, and follow around the coils of the wire, you will find that the magnetic field acts as if it is running through the hole inside of the loop. (If the loop were a donut, the magnetic field would go through the hole in the donut). Thinking along these lines... if we put a dozen donuts side to side, with a stick going through the holes, the magnetic field would follow the stick. Through experimentation, it was found that if a wire is wound in the form of a coil (coiled up), the total strength of the magnetic field around the coil will be magnified. This is because the magnetic fields of each turn add up to make one large resulting magnetic field. Furthermore, it was found that the direction of the magnetic field could be predicted. The POSITIVE end of the battery is ALWAYS connected to the NORTH POLE of the coil, regardless of whether the coil is wound clockwise or counterclockwise. The coil of wire, because of their properties and capabilities, makes up one of the main components in electronics. For this reason, it has taken on many names, to include: ELECTROMAGNET INDUCTOR SOLENOID COIL Coils have been given their own schematic symbol. So far we have discussed the schematic symbol for the resistor, lamp and battery. The schematic symbol for the coil is on the left. Note that there can be many variations of this, which will be discussed in more detail later.

There are several factors which determine the strength of a given electromagnet. They are: 1). The amount of current - the greater the current, the greater the field. 2). The number of turns - the greater the number of turns in a coil, the greater the field. 3). The PERMEABILITY of the core. The core of a coil is the material that the coil is wrapped around. It can be glass, wood, metal, air, or even a vacuum. If the coil is wound upon an iron core, the strength of the electromagnet is increased several hundred times over what it would be with an air core. We say that iron is more permeable than air. Permeability is the ability of a given substance to conduct magnetic lines of force. It is similar to the effect of conductance with respect to electrical current flow. The standard for permeability is air, which is given a permeability of one. All other substances are compared to air. Some examples of substances with high permeability are permalloy and iron. To the right is a picture of a " variable " air core coil. This particular coil is adjustable in value, based on a moving " tap " in the coil, which rolls along the outside of the coil as the spindle is turned. Sometimes this is called a " roller inductor ". As the spindle is turned, the coil itself rotates, and the tap moves along the length of the coil, changing its " electrical length ". Of course this is just one example of the many types and shapes of coils that exist. The key thing to remember is that any length of wire that is wrapped up into a coil, has the same electrical properties as a coil. Just as conductance has an opposite - resistance; permeability also has an opposite - reluctance. RELUCTANCE is mathematically the reciprocal of PERMEABILITY. The unit of measurement for reluctance is the REL or OERSTED , and its symbol is Ö . Voltage is the measurement for Amplitude of an electrical circuit. Magnetism also has a counterpart for this, which is called

MAGNETOMOTIVE FORCE . Magnetomotive force is the force which produces the magnetic lines of force or FLUX . The unit of magnetomotive force is the GILBERT , and its symbol is G . The formula for finding the value of G is as follows: G = N x I x 1.26 Where: N = the number of turns in the coil I = the current flowing through the coil in Amperes There is a catch phrase for N x I which is AMPERE-TURNS

The Relay Races
Knowing that magnetism and electronics are related is a very important lesson. Just how important will become evident in the next few lessons, as we will be discussing the interaction of electricity and magnetism in greater detail. Lets review some of the things we have learned: We know that when two magnets are brought close enough to each other, they will have one of two reactions. If their poles are the same polarity, they repel, or push away from each other. If, on the other hand, their poles are opposite, they attract, or pull toward each other. This is called the LAW OF POLES and it applies (to an extent) to electronics as well as with magnetics. Note that the electrons from the negative side of a battery will attract toward the positive side, if the two are brought electrically close enough to be allowed to do so. This typically happens by connecting a wire, lamp, or some other electrical device between the two electrical poles. If we think of electronics from this standpoint, the questions soon arises:

Does electricity move from positive to negative, or from negative to positive? This is a good time to discuss the fact that because we can not truly see the electrons in motion, but can only study their effects, there are 3 differing schools of thought on this subject, all of which have some merit. 1).According to the CONVENTIONAL THEORY of electron flow, also known as the FRANKLIN THEORY, or the POSITIVE CURRENT FLOW theory, electricity flows FROM POSITIVE TO NEGATIVE. 2).According to the EDISON THEORY , or the NEGATIVE CURRENT FLOW theory, electricity flows FROM NEGATIVE TO POSITIVE 3). According to the ELECTROMAGNETIC CURRENT FLOW theory, electricity, like magnetic lines of force, are free floating in space, and PUSH OR PULL WITH EQUAL FORCE IN BOTH DIRECTIONS . This theory, depending on the amounts of negative and positive energy, and the electrical proximity of the components between them, gives merit to either of the two above theories. Which of the 3 theories you choose to believe is totally up to you, but it would behoove you to remember the fact that there are 3 differing theories. Some writers write books based upon positive flow. Most modern authors choose to assume negative. But there are times when it is convenient to switch sides of the fence, in order to figure out exactly what is going on inside a circuit. The third theory is rare to find in books, however it does have its merits as well. The important point here is to make sure you know which theory your author is using, and try not to get too utterly confused. Another fact we know is that we can control the polarity of an electromagnet, by controlling the polarity of the voltage being fed into it. The North pole of the electromagnet is ALWAYS on the positive side of the battery. With this thought in mind, we can control the physical movement of a permanent magnet, by controlling the voltage going through a given

electromagnet. If we attach a battery to an electromagnet in such a way that it has the opposite polarity of a nearby permanent magnet, it will pull the permanent magnet closer to it. If we then swap the wires going to the battery, the electromagnet will change it's polarity, and the permanent magnet will be pushed away from it. If we physically attach the permanent magnet to a plunger, we can control the movement of the plunger in and out using electrical current. In this way, we use electric current to push a button, pull a lever, open or close a valve, or any number of other tasks. Because magnets attract ferrite based metals, we can also use electricity to control the physical movement of iron. In the examples given to the right, we are using electric current to move a type of reed switch. These are handy for allowing us to use a small amount of current to, for example, turn on a motor which needs a very large amount of current. In the case of the break contact relay, the reed switch inside the relay is constantly CLOSED (meaning connected), allowing current to flow through it. The motor is on all the time. When we connect the battery to our circuit via the switch, it will cause the magnet to pull at the iron reed, opening the switch, and turning the motor off. In the case of the make contact relay, the reed switch inside the relay is constantly OPEN (meaning disconnected), so no current is allowed to flow through it. The motor is normally turned off. When we connect the battery to our circuit via the switch, it will cause the magnet to push at the iron reed, closing the switch, and turning the motor on. Now would be a good time to show a schematic diagram and picture of a relay. The diagram to the left is an exact duplicate of the make contact relay circuit represented by the above picture. The break contact relay

schematic symbol would be similar, except the contacts would be connected. Keep in mind, that not all schematic symbols are standard. You may see variations of schematic symbols over the years, but they will all be understandable and descriptive of the function of the component. Below is a picture of a relay

The Meter Made
If we allow a current to flow through a coil of wire, it will generate a magnetic field. That magnetic field can be used to move nearby permanent magnets or ferrite metal components. We say that there is an induced magnetic field

radiating from the coil of wire. When the induced magnetic field cuts, or passes through, the magnetic field of the permanent magnet, it has the same effect of two magnets cutting each other's fields. In other words, it attracts or repels according to polarity.

We have seen how this can be used to our advantage in the case of the relay, but it has much more potential than that. If, for instance, we drill a hole in a magnet, and put an axle through it. If we mount the axle on a stand, we can spin the magnet upon it's axle by hand. Now if we place a coil near the magnet, we can make the magnet turn by controlling the polarity of the current through the wire. If we polarize the coil, such that the north side of the electromagnet is facing the permanent magnet, it will cause the north pole of the magnet to rotate away from the coil, while attracting the south side of the magnet toward the coil. The magnet spins 180 degrees. If we then change the polarity of the battery, so that the south side of the coil faces the permanent magnet, it causes the magnet to turn another 180 degrees, for a total of 360 degrees. We have caused the magnet to spin 360 degrees, and in effect, created a crude form of electric motor. The important point here is that we can use electromagnetic energy to make something turn, which brings us to one of the greatest leaps in electronic advancement - the D'ARSONVAL MOVEMENT. The D'Arsonval movement is the basis for all early metering devices, and is still in common use today. There are 5 basic parts to a D'Arsonval movement.
Permanent Magnet Coil Hair Spring Pointer Scale

In the D'Arsonval movement, the permanent magnet is fixed. It is the coil which does the turning. The coil is mounted on a needle fine axle, which would allow the coil to spin 360 degrees. The hair spring is used to return the needle to it's original position, as well as to regulate the movement of

the meter. The pointer, which is attached to the turning coil, is used for an indicator of how far the coil has turned. Finally, the scale is used as a numerical standard to compare readings. The D'Arsonval movement can be used by itself as a standalone instrument called a GALVANOMETER. The galvanometer is a device which indicates the presents of electrical current. It is not calibrated for Ohms, Volts, or Amps. By adding a high resistance in series with the D'Arsonval movement, we create a VOLTMETER. A Voltmeter is a device used to measure electrical potential in Volts. The series resistor is called a MULTIPLIER, and it's purpose is to limit the flow of current through the fragile meter movement. Given a known resistance, the Voltage read at the leads of a Voltmeter can be exactly calculated to cause a certain amount of current to flow through the coil of the meter. Armed with Ohms Law, and knowing the value of the resistor we use, we can calibrate the meter's scale to measure an exact amount of Voltage. We know that:
E R = --I Where: R = Multiplier Resistance E = Full Scale Voltage I = Full Scale Reading of Meter

So it follows that given a meter movement that deflects full scale when 1 milliampere flows through it, We can find the value of the multiplier resistor that is necessary by using the following formula:
1000 x E R = --------I

If we measure the Voltage across the circuit in the diagram above, we find that E = 400 Volts. (NOTE THAT VOLTAGE IS ALWAYS MEASURED IN PARALLEL),

1000 x 400 R = ----------I

400K = --------1.0 Amps

Knowing, then, that we have a 400KΩ Resistor, and it requires a 400 Volt potential to cause full deflection we divide the meter resistance by the full scale voltage and come up with the sensitivity of the meter.
meter resistance R = ----------full scale voltage 400K Ohms = --------- = 1000 Ohms per Volt sensitivity. 400 Volts

Other Types of Meters
The Voltmeter is very handy in electronics work. But there are times when other meters are needed to do the job. And many of these meters are also built upon the D'Arsonval movement. For instance, how would you measure the resistance of a resistor that is not in a circuit? This would require the use of an Ohmmeter. Or what if you wanted to know the amount of current flowing through a circuit, so that you knew what size of fuse to put in the circuit? You would need an Ammeter to measure the current in Amps. Recall that the Voltmeter had a resistor in series with it. This resistor, called the "Multiplier Resistor" was used to calibrate the meter to work within a given range. A Voltmeter is also placed in parallel with the circuit in test. An Ammeter, on the other hand, is built with a resistor in PARALLEL or in SHUNT with the D'Arsonval movement's coil. In the case of the Ammeter, the SHUNT resistor is of a very low resistance. Much lower

resistance, in fact, than the coil in the meter movement. Remember finding resistance in a parallel circuit? The two resistors in parallel carry more current than either of the resistors by themselves. This is because the combined resistance is lower than the lowest resistor in the parallel network. Also, the resistor with the lowest resistance always carries the greatest current. This is of utmost importance here. If too much current were to go through our sensitive meter coil, it would burn up and destroy the coil, hence making the meter useless. The answer, of course, is to make sure that no matter HOW high the current, the majority of the current will always flow through the shunt resistor. It is for this reason that the shunt resistor has a lower resistance value than the coil winding of the meter itself. The formula we use for finding the value of the shunt resistor is as follows: Where: R s = shunt resistance R m = meter movement resistance I m = full scale meter movement current I s = shunt current The Ammeter, unlike the Voltmeter, is not used in parallel with the circuit in test. Rather, the ammeter is placed in series with the circuit essentially becoming an integral part of the circuit in test. If a Voltmeter were to be removed from a circuit in test, the circuit would continue to run. If an Ammeter were to be removed while the circuit were running, the circuit would shut down, because there would no longer be continuity or flow of electricity. Finally, the Ohmmeter is one of the most used tools on the electronics workbench. It is used not only to measure the resistance value of a given resistor or circuit component, but also to check continuity of wire, to test for opens and shorts in a circuit, and many other things. But an ohmmeter is not self sufficient. The Ohmmeter is made up of an Ammeter, a battery, and a

CURRENT LIMITING RESISTOR . As shown in the picture to the side, the battery causes a current to flow through the meter. We know the value of the current limiting resistor, so if we short the meter leads together, we know how much current the meter should indicate. If the meter indicates a lower current value than we expected, then there must be some added resistance. Therefore, we can use this device to detect, and to measure the value, of an outside resistance.

Magnetic Induction - The Flip Side

previously, we discussed the fact that a wire conducting an electric current, generates a magnetic field around it. Along the same lines, when a magnetic field, radiating from a permanent magnet, passes through a wire or coil of wire, it induces an electrical current on the wire. To state this another way, just as a current in a wire generates a magnetic field - a magnetic field passing through a wire generates a current. We can monitor this action by placing a meter across the wire. When we approach a wire with a magnet, the wire cuts the magnetic field and we see the meter needle move. In this way, we can "generate" electricity by moving a magnet in close proximity to a wire. The stronger the magnetic field, the more current flows through the wire. There is a catch though. If we stop the movement of the wire, right in the middle of the field, one would think that electrical current would continue to be generated. Actually, this is not the case. The magnetic field must be moving in relation to the wire in order for a current to be generated in the wire. In other words, either the magnet, or the wire must be moving. And the faster the wire passes through the field, the more current is generated. Now we know that according to the physical law of CONSERVATION OF ENERGY that no energy is ever lost or gained. So the energy generated in the wire can't just come out of the blue. It must be transformed from some other sort of energy. The question being, does it come from the magnetic field, or from the motion? The answer is that the energy is transformed from mechanical momentum into electrical current. This is the principle behind an electric generator. If we take a wire coil, and place it on a rotating shaft, then we can spin the coil. If the shaft runs midway

between two permanent magnets, we can control the movement of a coil of wire between two magnetic poles. Thus, it is possible to generate electricity by spinning the coil upon the shaft, because the wire is in constant motion within the magnetic field. The motion is transformed into electricity via the magnets. The electricity goes out to the world from the terminals, by way of the brushes and slip rings. This will be explained in more detail in a later lesson. The important point to remember is that we can generate magnetism with a wire conducting electricity, and we can generate electricity with magnets.

A C Theory
Earlier we discussed that there are various ways to produce electricity. We can produce electricity chemically with a battery. We just learned that electricity can be produced mechanically by a generator. What we did not discuss in detail, though, was the difference between electricity produced by a battery, and electricity produced by a generator. In the case of a battery, electricity flows in one direction, from positive to negative. Everything is straightforward. In the case of a generator, however, things get a bit more complicated. It is possible to generate electricity by spinning a coil within a magnetic field. The coil is in constant motion within the magnetic field, and thus is transformed into electricity via the magnets. The electricity exits by way of the brushes and slip rings, but it is not exactly like the electricity which is produced by a battery. If we look at the current leaving the battery, it is constantly moving in the same direction. We call this DIRECT CURRENT . But if we attach a generator instead of a battery in the same circuit, we notice a major change. The meter would swing back and forth from negative to positive. This seems strange until we examine what is going on inside the generator.

As the wire coil rotates, it first passes the north pole of the magnet, producing an electric current flowing in a given direction. As the coil continues in it's circuilar path, it passes the north pole, moving toward the south. As it approaches the south pole, the electric current begins to flow in the OPPOSITE direction from which it was originally moving. It continues to move in this direction until, once again, it aproaches the north pole. We say, then that the electrical current is ALTERNATING between positive and negative. We call this type of current ALTERNATING CURRENT . If we were to plot this swing from positive to negative on a graph, and compare it to the time it takes the motor to turn, we would come up with something like the chart to the left. Notice, that if we begin with the coil positioned directly in the center, between the permanent magnets, the current output is 0. However as the coil begins to turn, one side of the coil moves toward the north pole. This end of the wire would become positive. At the same time, the other side of the coil moves toward the south pole. This side of the coil becomes negative. At this time, current begins to flow from the positive to the negative. Current continues to flow in this direction and reaches a peak in its cycle. This Maximum amount of current flow is reached when the coil is pointing exactly north and south. We call this the 90 o point, and say that the signal has reached it's positive peak. After it passes this point, the voltage begins to drop, but doesn't reach 0 until once again the coil is positioned directly between the permanent magnets. This is the 180 o point. Now comes the switch up. As the coil continues to turn, the end that was positive now moves toward the south pole of the magnet. Because it is passing by the south pole, this end of the coil swings negative. At the same time, the side of the coil that was negative, is now swinging positive. Thus, the direction of current flow within the wire is switched. The current flow continues in this direction until it again reaches a (this time negative) peak at 270 o . Finally, as the coil aproaches it's origional position, it swings positive until current flow again reaches 0. By graphing the current vs. time, we end up with a pattern known as a SINUSOIDAL WAVE , or SINE WAVE for short. We say that the sine wave has positive and negative peeks at 90 o and 270 o respectively

Characteristics of a Sine Wave
As stated before, by graphing the current vs. time, we end up with a pattern known as a SINUSOIDAL WAVE, or SINE WAVE for short. We say that the sine wave has positive and negative peaks at 90 o and 270o respectively. A sine wave has several important characteristics. 1. One complete revolution of a generator, from 0o to 360o, is known as a CYCLE. 2. The DISTANCE between the beginning of one cycle, and the beginning of the next cycle is called one WAVELENGTH. The symbol for WAVELENGTH in electronics is the greek letter lambda ( λ). 3. The TIME in which it takes to complete one cycle is known as a PERIOD. 4. The number of complete sine wave cycles generated in one second, is called FREQUENCY, and is measured in CYCLES PER SECOND (cps), PERIODS PER SECOND (pps) or more often HERTZ(Hz). 5. The height of the sine wave is called the AMPLITUDE, and is measured in Voltage. The highest point of any wave is called the PEAK AMPLITUDE or PEAK VOLTAGE. 6. The difference in amplitude between the highest positive voltage, and the highest negative voltage is called the PEAK TO PEAK VOLTAGE, which is equal to twice the peak Voltage.

Now without going into a whole bunch of math and physics...(yea, RIGHT!)... you learned sometime in your life that there is a relationship between distance, time, and speed. If you are driving down a road at 50 miles per hour, for exactly one hour, you know from basic math that you will have travelled exactly 50 miles. Why? Distance = Speed x Time This is a basic law of physics. It also applies to electricity and waves. If a Wavelength is a length (read: Distance) then we can use time to compare the speed at which it travels through space. Now electricity travels at the speed of light, but what exactly is that? Well, it differs slightly from one medium to another, but for our purposes, we will assume the speed of light in a vacuum. Wavelength = Speed x Time We know that 1. Speed of light = 299,792,458 meters/second (In a perfect vacuum) 2. Time = (299,792,458) Speed / Distance (λ ) If we assume a signal with a 2 meter long wavelength, we can use the following formula to find the time that it takes to complete one cycle:

Using this formula we can plug in the numbers

Now by simple division, we get the following answer:

Now if a 2 meter long signal is equal to 6.67 nanoseconds, we can find the frequency of the signal as follows:

Let's plug in the numbers...

Since we know that 149MHz = 2 meters in length, we can deduce that frequency and wavelength have a relationship such that: Wavelength (in meters) = 298 / Frequency (in MHZ) or if you prefer: Wavelength (in feet) = 936 / Frequency (in MHZ) Let us test this theory. The 11 meter band, otherwise known as the CB Radio, or Citizen's Band, resides at (aprox.) 27 MHZ. Does the math work out?

The formulas you can look up in the future, should you need them. The basic knowledge we have tried to stress here is, that WAVELENGTH is a DISTANCE, a PERIOD is an amount of TIME, and that FREQUENCY is the number of wavelengths in a second. Furthermore, we stressed that all of these terms are related, but not quite interchangable.

It Won't Even Phase You
So far, we have discussed that Sine waves have FREQUENCY, WAVELENGTH, PERIOD, and AMPLITUDE. They also have one more important characteristic: PHASE Phase is the timing relationship between two different sine waves. If two generators are connected across a given load in series, and if their armatures begin rotating together at exactly the same time and speed, two different alternating voltages will be produced. In the example to the left, one is a 4 Volt sine wave, and the second is a 3 Volt sine wave. If we examine the picture closely, we find that both sine waves meet up at the 0o and 180o points. Furthermore, they both peak out at 90o and 270o respectively. We say, then, that both of the two waves produced by the two different generators are IN PHASE with each other. Whenever two waves are in phase, like these are, the voltage resulting from the two waves will not be the same as either of the two voltages. The resulting voltage will be the SUM of the two voltages. In this case, we have 3 and 4 volts being produced by the generators, and the resulting output voltage would be 3+4 or 7 Volts. This is because the energy in the two voltages work together, and combine to add up to 7 Volts. But what happens if the generators are NOT in phase? Whenever two waves are combined out of phase, the resultant waveform is not so simple to figure out. Look at the picture on the right. The 3 Volt generator was started later than the 4 Volt generator. We say that the 3 Volt wave LAGS behind the 4 volt wave. In this case, the 3 Volt wave LAGS by 90o. Voltages that are out of phase can not be added simply by adding them together, as we

do with in phase waves. We must resort to a sort of "high math" called VECTOR ADDITION. To make it simpler to understand, Vector math simply means that we break out a piece of graph paper, and plot the 3 volt wave horizontaly (left and right), while we plot the 4 volt wave vertically (up and down). Examine the chart to the left to see how this works. Using our 3 and 4 volt waves, we draw the two lines on the graph paper. Then we draw a "mirror image" of the same two lines. When we are finished drawing the mirror image, it should form a parallelogram. Now we draw a diaganol line from the "0" point in the middle of the graph, to it's opposite corner of the parallogram. The distance from the 0 point to its opposite corner will be the vectoral sum of the two voltages. This method works, no matter what the Phase difference is between the two voltages, but does require a little modification if it is different from 90o. Let us assume now, that instead of the two waves being 90 degrees out of phase, that the 4 Volt wave is lagging the 3 volt wave by 45 o this time. The method of finding their vectoral sum is basically the same. First we plot the 3 Volt wave horizontally on the chart. Next we measure 45 o to draw the second line. We draw the 4 Volt line 45o from the 3 Volt wave. Now again we draw a parallelogram, reflecting the origional two plotted voltages. We draw a line bisecting the parallelogram from the 0 point to its opposite corner. The length of the resultant line indicates the vectoral sum of the two original voltages.

ACK!

It's A.C. !!!

Ok, so now that you think you've had enough with math, you find that AC has more complicated math than DC does. But the fun isn't quite over yet. You've got to be able to convert AC voltage to their DC equivalent voltages, and visa versa. The main problem is with Voltage. DC Voltage is straightforward. If it's 10 Volts, it's 10 Volts - period. But with AC, Voltage becomes more difficult to define. Looking at an AC wave, we actually have 3 different voltages to compare. The voltage from the 0 line to the positive peak of the AC curve is called the PEAK VOLTAGE. If we measure the Voltage from the top of the positive peak, to the bottom of the Negative peak, we call it the PEAK TO PEAK VOLTAGE, which is equal to 2 times the peak voltage. Finally, when we try to do work with an AC Voltage, we find out that a 10 Volt peak voltage wont turn a motor as fast as a 10 Volt DC Voltage. Reason? Because 10 Volts DC is 10 Volts all the time. A 10 Volt peak AC Voltage is only 10 Volts for an instant. The rest of the time it is swinging higher and lower in Voltage level. So at what Voltage level does the AC wave do as much work as a pure DC Voltage?

It was found that it takes a 141 Volt AC wave to do the same amount of work as a 100 Volt DC source. The EFFECTIVE value of a 141 Volt AC source then is only 100 Volts. Another term for EFFECTIVE voltage is RMS, which stands for Root Mean Square. Often, electricians and electronics technicians find that they need to be able to convert AC voltages to DC voltages. They need to know what the effective voltage is. Based on the 141:100 ratio of AC to DC, the following formulae were conceived:

Where Epeak equals the peak voltage of an AC signal and Eeff equals it's effective (RMS) DC equivalent.

Just when you thought it was safe to get back into the water, I'm gonna throw one more formula at you. What happens if we take all the instantaneous voltage values of a sine wave, add them all up, and then take the average of them? Well, it doesn't quite come up to the effective voltage. When working with rectifier circuits (we'll discuss them in a later section), we must sometimes use what is known as the AVERAGE VOLTAGE of a given AC sine wave. The average voltage is found by the following formula:

Enough is Enough !!
Ok, a human being can only be subjected to so much math before their head explodes. I don't know about you, but I've about reached my limit for now. So let's discuss something a little less math intensive. We spoke earlier of the ability of a wire to produce a magnetic field when a current is flowing through it. We say that the current is INDUCING the magnetic field. We also stated that this inductance becomes stronger when the wire is wound up into a coil. But this is not the only factor which effects the amount of inductance within a coil. There are actually 4 factors which determine the inductance of a coil of wire: 1. The number of turns in the coil. 2. The material that the CORE of the coil is made of. 3. The length of the coil. 4. The diameter of the coil NUMBER OF TURNS: If we have two coils of identical length and diameter, but one has 4 turns of wire, while the second has 8 turns of wire, the coil with 8 turns will have more inductance than the one with 4 turns. CORE MATERIAL: A coil wrapped around an iron core will have a much greater inductance than one wound with nothing in the middle but air. This is because iron has a much higher PERMEABILITY than air. LENGTH OF COIL: If the coil has the same diameter, and the same number of turns, but is made longer (say, by stretching it out), the inductance of the coil will decrease. DIAMETER OF COIL:

If the coil is the same length and number of turns, but smaller in diameter, the inductance will also be smaller. Now we could go into the math and physics of why the coil increases or decreases with size, shape, number of turns, etc, but that is not the scope of this course. A basic general understanding of inductance is all you need at this point. So let us first explain what inductance is and how it works. When we first created our coil of wire, we were working with DC. Now we are learning a little about AC, and as you've found from the math.... the game changes some. When we attach a battery to our coil, it induces a magnetic field. This magnetic field does not, however, appear instantly, as one might believe. You see, electricity, as we have found, moves at a given speed (the speed of light). It travels the distance of the wire, depending upon it's length. Now we know that there is a special relationship between speed and distance, in that it takes TIME for something to travel a distance at a given speed. Prior to our attaching the battery (we'll assume a 12 Volt battery for our discussion), the potential difference between the two ends of the wire is 0 Volts, and the current flowing through the wire is zero. As we attach the battery, the wire, which has resistance, enforces Ohm's Law. The Voltage (now 12V), divided by the resistance of the wire sets up a current within the wire. That current begins at one end of the wire, moving throught the wire until it reaches the other end. During the time period of time that the current begins movement (0 speed), to the time it reaches its maximum speed, it is accelerating. Of course, when we disconnect the battery, we have an opposite effect, and for some time, the current is decelerating. The important point here is that the current speeds up and slows down within the coil whenever we attach or detach the voltage source. Now for AC: As we use an ALTERNATING current source, we know that the Voltage is in a constant state of change, fluxuating from 0 Volts, up to a maximum positive peak, back down to 0, continuing to a negative peak, then returning again to it's starting point of 0 Volts. It takes TIME for this to happen. Now if we attach this

fluxuating voltage source to a coil, the voltage is in a constant state of change. As the AC generator begins it's upward curve, the voltage in the coil is 0 Volts. As the voltage reaches its positive peak, recall that it takes time for the electric current to flow, the voltage in the coil is beginning to rise, and a NORTH magnetic pole is beginning to be formed. As the coil reaches its peak of current, the alternator has rotated to it's point of 0 Volts and is beginning to swing negative. (Can you predict what is coming?) As the alternator swings negative, it forces current through the wire in the opposite direction. At the same time, the magnetic field in the coil attempts to collapse, by inducing it's magnetic field into the wire in the same direction it was originally moving. The current that the magnetic field is producing, is in direct opposition to the current that the generator is now producing. Of course, the magnetic field is small, and has less staying power than the generator, which has force and momentum behind it. So the generator wins and pushes the current through the coil, now forming a SOUTH pole on the electromagnetic coil. So as the generator is swinging from positive to negative, the coil is swinging from North to South, expanding and collapsing between Voltage peaks. In addition, the coil is slightly out of phase (remember that word?) with the generator, and hence, is opposing the flow of electric current. Isn't that the definition of RESISTANCE? The coil RESISTS the flow of AC, but allows DC to pass freely. INDUCTANCE is defined as the opposition to any change in current flow. It is NOT the opposition to current flow, but the opposition to CHANGE of the flow. It is a form of light resistance caused by the collapsing magnetic field opposing the CHANGE in current within the coil. Did we say that a coil acts like a resistor in some circumstances? Yup, sure did! Then it must follow Ohm's Law, huh? Yup, sure does! Not only does the wire itself have resistance, but the coil resists AC current flow. But Ohm's law doesn't EXACTLY apply in the same way, and for now, you've had enough math, so I won't throw that at you right away. What you should consider, though, is that inductors can be act like resistors in parallel circuits. This means that you solve for inductance, the same way you solve for resistance in a series circuit.... you add the value of the inductors. Along the same lines, in a parallel circuit, you would "reciprocate the sum of the reciprocals" of indivual inductances.

Mutual Inductance and Inductive Reactance
I promissed no more math in the last session, and it was difficult. We could have covered the number of turns to inductance:

but we didn't. We could have covered the math behind inductors in parallel:

but we didn't. But we will cover just a little math in this lesson. When AC is applied to a coil, a varying magnetic field will be produced around it. When another coil is placed within that magnetic field, it will induce a current flowing in that coil. This principle is called MUTUAL INDUCTANCE The amount of mutual inductance between the two coils depends on the distance between the two coils, and the angle between the two coils. When two coils are linked together via mutual inductance in this manner, we say that the coils are inductively COUPLED. When the mutually inductive coils are close to each other, we say that they are closely, or tightly coupled. When they are far apart, we say that they are loosely coupled. The greatest amount of coupling occurs when the coils are wound one directly over the other and on a closed iron core. The quantity of coupling between two coils is sometimes referred to as the Coefficient of Coupling. The formula for Coefficient of Coupling is:

Whew! Now that we've got the math out of the way, let's move on to the magic of electronics. We have already discussed that inductance is an opposition to the flow of current in an AC circuit by a coil. This is caused by the expanding and collapsing of the magnetic field. More important though, as the field

expands and collapses, it generates a counter- electromotive force, by way of mutual inductance within the same coil. We call this SELF INDUCTANCE. Simply put, self inductance is when a coils magnetic field, produces an electric current within the same coil. This self inductance causes a resistance to AC current. But this resistance is not measured in Ohms, as normal resistance is. This resistance isn't even called resistance, it's called REACTANCE, because of the way it reacts with AC. In the case of a coil, it is specifically called INDUCTIVE REACTANCE, and it's symbol is XL. XL is a very special number in electronics. Let me say this another way:

XL is a very special number!
get the idea? Now that I have your attention. XL is the variable number that we use while expressing the AC resistance of a coil. You will see this number in your sleep. You will eat with this number, you will go out on dates with this number and you will MEMORIZE THIS FORMULA:

XL = 2πfL
Where: • f = the FREQUENCY in Hz • L= the inductance of the coil in henries and • π= 3.1415926536..... (or 3.14 for short)

Inductive Reactance Revisited
TEST TIME! 1. What is the formula for finding Resistance, Voltage, and Current? CLICK FOR ANSWER

2. What is the formula for finding Total Resistance in a SERIES

circuit? CLICK FOR ANSWER 3. What is the formula for Inductive Reactance? CLICK FOR ANSWER

Ok, perhaps I have stressed this point a bit too far, but then again, in electronics, and especially in radio electronics, you will see this formula again and again. Inductive reactance constitutes the resistance seen by an AC circuit when it runs into a coil. Sometimes, an inductor is called a CHOKE, because it chokes an alternating current flow. In power supplies, you may find a FILTER CHOKE, which opposes any ac frequencies, while allowing DC to pass through unharmed. Its purpose is to clean up the power supply voltages, so that no noise is seen on the power - just a clean DC source. There are both audio frequency chokes (AFC) and radio frequency chokes (RFC). Another point, which I passed over previousely, is that there are several types of "RESISTANCE" found in AC electronics, some of which will be negligable, others you will find fascinating and extremely important to the study of electronics. I will try to cover in detail the important ones. I will also, (when I remember to) mention the lesser important ones, as I will at this time. RELUCTANCE is a form of resistance which we have not discussed yet. The reason for not discussing it, is that in most electronic applications, you can pretend that it doesn't exist. Reluctance is actually the resistance, not to the flow of current, but to any MAGNETIC FIELD which cuts through any pre-existing magnetic field. To some small extent, this happens in all coils operating at AC, due to Self Inductance, or by way of Mutual Inductance. Mathematically speaking (oh no!) we say that it is equal to the MAGNETOMOTIVE FORCE / MAGNETIC FLUX, or that it is the reciprocal of PERMEANCE. Now, don't you feel safer? Isn't your life better, since you have learned that bit of trivia?

Capacitor - a new component
So far, we have studied the effects of electricity flowing through wires, and

have discussed resistors, coils, and metering devices. Both resistors and coils, as we have found, have a restricting effect on the flow of current. We also discussed how a coil has more resistance to AC than it does to DC. You will learn later just how important these effects are, but first we must discuss a few more electrical components. Another component which has a restricting effect on current flow, but in a different way. This component is called the CAPACITOR. Once again, we will resort to our water examples to describe the function of a capacitor, as it is easier to see fluid in motion, when it is water, than when it is electricity. Examine the example on the left. Here we have 2 tanks of water, equally full. The two tanks are connected in the middle by a pipe or piece of tubing. Let us say now that we have, in the middle of the tubing, a thin rubber membrane. The membrane would keep the liquid in the two tanks from ever coming into contact with each other. We could further illustrate this by adding food coloring to one of the tanks of water. If we now take a plunger, and apply pressure to the tank on the left, it will push the water downward, and try to push it out the tube and into the other tank. However, the membrane will not allow the water to actually exit the tank, and enter the second tank. While the two systems are sealed off from one another, the rubber membrane would flex, and allow the EFFECT of movement, in that it would push the water level of the second tank higher, in direct proportion to the movement in the first tank. For instance, assuming both tanks are of equal diameter, if the first tank went down 2 inches, the second tank would rise 2 inches.

Now, if we should reverse the action, and push the plunger down in the second tank, it would move the membrane in the opposite direction, also moving the water within the tanks in the opposite direction, but AT NO TIME would the water flow from one tank into the other tank. It would have the effect of movement from one tank to the other, without actually having done so. This is basically the same operating principle behind another of electronics most important components - the capacitor. The capacitor appears to have the effect of passing alternating current, while actually not passing anything. At the same time, it blocks the flow of direct current. Just as in the water circuit, the water flow in either given direction is blocked by the membrane, if we should push the water pressure, and hence the membrane back and forth, it would appear as if the membrane weren't there at all, except that the food coloring would not pass from one container to the other. In its most basic form, a capacitor is made up of 2 plates of conducting material (for instance copper, aluminium, iron), divided by a piece of insulative material (for instance mica, air, or plastic). When we apply an electric potential to the two plates, electricity will want to attract and flow from one plate to the other, but the insulator will act as the membrane, and block the flow of electricity. For this reason, a capacitor blocks the flow of DC. As power is applied, a certain number of electrons on one plate will be attracted to the positive side of the battery. These electrons, leaving the plate will leave it with a deficiency of electrons, and the plate will be positively charged.

At the same time, electrons from the negative side of the battery will see the positive charge on the plate, and want to move toward it. As these electrons leave the negative side of the battery, they will pass through our light bulb, and light it. We will notice, however that it only lights for a moment.... just a split second! Why? Because between the two plates of the capacitor is an insulator, and while the electrons on the negative side may be attracted to the plate on the positive side, the electric current can't pass through the insulator. So our light flashes for just a second, and then goes out.

Now if we reverse the polarity of the battery, we see that the same thing happens again, only in reverse. As power is applied, the electrons on the now negativly charged plate of the capacitor will be attracted to the positive side of the battery. As these electrons now leave the plate, it will leave a deficiency of electrons, and the formerly negative plate will become positively charged. At the same time, the electrons from the negative side of the battery will move toward the positively charged plate until the positive plate swings negative. Note that in the examples, the schematic symbol for the capacitor is very similar to that of the battery. There is good reason for this. In a battery, we have 2 (or more) conductive plates divided by some kind of dialectric material (usually an acid). In a capacitor, we have 2 (or more) plates divided by some kind of dialectric material - an insulator. A battery has the ability to generate electricity chemically, and can store energy for long periods of time. While a capacitor does not "generate" electricity, it does have some amazing "storage" capabilities, as we will discuss now. Recall that when we applied power to the capacitor/lamp circuit, electric current flowed for an instant from one side of the battery and lit the lamp for a moment, but then the light went out? What took place, was while the electric current was flowing, a potential was being built up on the surface of the plates of the capacitor. As long as the potential kept building, current continued to flow, and the light remained lit. At some point, however, the capacitor reaches its maximum CAPACITY to hold an electric potential. In other words, it reaches its peak voltage limit, and we say the capacitor is fully charged. If at this time, we were to remove the battery from the circuit, the capacitor, in theory, would remain at full charge indefinately. If at this time, we shorted the wires between the capacitor and lamp, such that it formed a complete circuit, the lamp would light for just a second..... WITHOUT THE BATTERY. Where does the energy come from to light the lamp if the battery is not connected? The answer lies in one of the magical properties of the capacitor....it can

STORE energy! When energy is stored in a capacitor, we say it is charged. When a capacitor releases it's energy, we say it is discharging. Capacitors come in many shapes and sizes, and each type has its very own special characteristics. To the right is a small example of the variety. The most important values to keep in mind when replacing a capacitor are voltage and capacitance value. Depending on the circuit, it is usually acceptable to use a capacitor of a higher voltage rating that the one being replaced, but the capacitance value must remain the same. Also keep in mind that some capacitors, especially electrolytics, may be polarized positive and negative. If you accidentally reverse the polarity, severe circuit damage, as well as possible injury, may occur. Always pay attention to which way you remove a component from circuit. The symbol for Capacitance is C. The unit of capacitance is the FARAD. The symbol for Farads is F. The Farad is an extremely large quantity, so we typically speak of microfarads ( μf ), nanofarads ( nf ), and picofarads ( pf ). * Note: in some older texts, the term micromicrofarad ( mmf ) is used in lieu of pf. The Capacitance (the amount of energy a capacitor can store) of a capacitor depends on 3 factors: 1. The Area of the plates 2. The Distance between the Plates

3. The Type of Dialectric

The formula for capacitance is: Where C is the capacitance in picofarads, A is the area of one of the plates in square inches, and K is the dilectric constant of the insulative material seperating the plates.

ELI the ICE man

In a previous lesson, we covered the fact that two alternating currents can be either in phase, or out of phase with respect to each other. We also discussed the addition of two sine waves of differing phase by using VECTOR ADDITION. I am fairly certain that you were hoping you would never see this again. Sorry, but you were SO wrong. We are soon going to get into the practical applications of vector addition. You are about to learn that in electronics, the capacitor and the inductor are exact opposites. The reason for this is because they BOTH store electricity, but in different ways. In a purely resistive circuit, there is no change in the phase from one component to another. When we add an inductor or capacitor into the circuit, however, the game changes completely, and the rules to the game are written with vectoral math. Note that if we were to find the resistance of a series circuit with 2 resistors, one having 3 ohms, and the other having 4 ohms, we would simply add them, and come up with 7 ohms. If we were to graph this, we would have a single line along the "X" coordinate which is 7 units long, with points at 0, 3, and 7. If, however, we were to plot the Combined Resistance of a coil ( remember XL ? ) and a resistor we would have to plot a graph like the one above and to the left. This combined resistance is called IMPEDANCE, which is the TOTAL RESISTANCE TO THE FLOW of current. The symbol for impedance is Z. If you have ever studied trigenometry, or even basic geometry, you may recall the formula for finding the hypotenuse of a right triangle ( A 2+B2=C2). This will come in handy, as you compare it to the formula for impedance:

R2+XL2=Z2
This can be re-written as

Now let's assume that we have a series circuit like the one shown on the left. Using the formula for IMPEDANCE ( Z ), R2 would be 32 which equals 9. XL2 would be 42 which would be 16. 9+16=25. The square root of 25 = 5, so the impedance of the circuit would be Z=5. Sometimes we might say that the "complex representation" of Z = R+Xj. In this case it would be 3+4j. This comes in handy as we begin adding capacitors into the circuit. Capacitors are like the opposite of inductors in a circuit. Whereas inductors are added ( Z = R + Xj ).... capacitors are subtracted (Z = R - Xj ). I know this all sounds confusing, but it will become clear as mud shortly. Recall the formula for Inductive Reactance?

XL = 2πfL
How could you forget? Well, CAPACITIVE REACTANCE is it's opposite, and should also be memorized. Ready for this one?

1 XC = ---------------2πfC
WOW! It's almost the same formula! The only difference is that we substituted the L's for C's, and we reciprocated the formula (divided 1 by the formula). In the great scheme of things, that makes this formula not too difficult to remember, assuming you did memorize the formula for inductive reactance when I told you to. If you didn't, take time now to memorize both formulas. Your survival in electronics depends on them. Notice that I have flashed lots of formulas by you, but I have only asked you to memorize 3 of them... Ohm's Law, and the formula's for inductive and capacitive reactance. That is because you will use them over, and over again.

Now let us examine our capacitive circuit. Once again, it has a resistance of 3, and a reactance of 4, but this time, it is a capacitive reactance, and not an inductive reactance. We will again use the formula for IMPEDANCE ( Z ), R2 would be 32 which equals 9. XC2 would be 42 which would still be 16. 9+16=25. The square root of 25 = 5, so the impedance of the circuit would once again be Z=5. But there is a catch - this time, because the circuit is CAPACITIVE, we would have a complex representation of impedance being equal to 3 - 4j. What exactly does this mean? It means that instead of plotting our graph in the POSITIVE direction along the Y axis of our graph, we would plot it in the NEGATIVE direction. Instead of our plotted point being (3,4) it would be located at (3,-4). I realize, of course, this is a lot of math to remember, but unless you are designing radio frequency, or other resonant circuits, you probably won't be using these formulas on a daily basis. You should be familiar with them though, and you SHOULD memorize the formulas I have pointed out thus far. One important point to keep in mind, is that when current flows through a purely resistive circuit, the voltage and current arrive at the same point at the same time. In other words, Voltage and Current are in phase in a purely resistive circuit. In a circuit which contains inductance or capacitance though this is not so. In an inductive circuit, the voltage leads the current by 90 degrees (assuming a purely inductive circuit). Likewise, in a capacitive circuit, the current leads the voltage by 90 degrees. Which leads which is easy to remember. Just think "Eli the Ice man". E=Voltage I=Current... L=Inductor......C=Capacitor • ELI Inductive circuit...... Voltage arrives before Current . • ICE Capacitive circuit... Current arrives before Voltage.

More about Coils and Caps
Remember series and parallel circuits? I know it's been quite a while since we studied them, but it would do good to review a bit before we get too entangled in other stuff. Resistors o Added in Series (R1+R2+R3) o Reciprocate the Reciprocal in Parallel 1 -----------1 1 ---- + ---R1 R2 Coils
o o

Added in Series (L1+L2+L3) Reciprocate the Reciprocal in Parallel 1 -----------1 1 ---- + ---L1 L2

Capacitors: Remember.... the capacitor works OPPOSITE the coil.
o

Reciprocate the Reciprocal in SERIES
1 -----------1 1 ---- + ---C1 C2

o

Added in PARALLEL (C1+C2+C3)

RL and RC Time Constants.
Recall that in our lamp and cap circuit, the lamp lights up for a second, but then goes out. What determines how long the lamp stays light? The lamp is not a perfect device which generates light from electricity. It has losses, and shows electrical friction (read: resistance). Any time that you have a resistor and a capacitor in a circuit, we call it an RC circuit. Likewise, if there is a resistor and a coil in a circuit, we call it an RL circuit. In this circuit, the moment the battery is applied, current starts to flow through the resistor, and a voltage begins to build up across the plates of the capacitor. The amount of time that it takes for the voltage across the capacitor plates to reach the voltage of the battery, is a result of the values of the capacitor and the resistor. The larger these two values are, the longer it will take for the entire voltage to appear across the cap. This relationship is expressed by a formula, and is called "Time Constant". The formula is:

T = RC
where T= Time in seconds, R=resistance in ohms, and C=capacitance in farads. A time constant also exists between coils and resistors, however, because of the nature of how a coil is made (it is essentially a piece of wire), time constants in RL circuits are much smaller. Recall that earlier in the course, we discussed that inductors and capacitors are almost exact opposites. Here is another formula which will seem re-hashed.

T=L/R
where T= Time in seconds, R=resistance in ohms, and L=inductance in henries. Remember this formula?

XL = 2πfL
Well, you are going to have to start using XL and XC again. Because we are going to begin using capacitors and coils in the same circuit. Now the real fun of electronics begins.

Resonance / Black Magic 101.
In this circuit, we have a resistor, a capacitor, and a coil in series. Because the coil and the capacitor act in an opposite manner, they tend to cancel each other out. We say that the coil is additive, and the cap is subtractive in nature. If the inductive reactance, and the capacitive reactance were equal in value, they would effectively cancel each other completely out, and only the resistance would be seen. In this special

case, we would say that we have a resonant circuit (we'll explain the term in more detail in a little bit). Just as we must solve problems with resistance in series... we must also be able to add the various reactances together, and come up with a common ground. Resistance is pure resistance. Capacitive reactance is a resistance that is subtractive in nature. Inductive reactance is additive in nature. Combining the three, we come up with a new term called IMPEDANCE, which is symbolized by the letter Z. Just like resistance, the formula is different for impedance in series and in parallel. The formula for impedance in series is:

If we plug in the values in the example above, we can solve the formula like so:

Note that this method is not much different than what we did in lesson 25. There we added phase "vectorally". This is a function of trigenometry, where in a given triangle, A2+B2=C2. (The square of the hypotenuse is equal to the sum of the square of the two sides). The same applies here. We can say that the A2 is the resistance, the B2 is the combined capacitive and inductive reactances, and the C2 is the Impedance ( Z ).

We could plot out our capacitance and inductance vectorally, but this would use up lots of time and paper. We can simply solve the same problem using this formula, where the B2 is equal to the sum of the reactances of the coil and the cap. We always subtract the capacitive reactance from the inductive reactance, because capacitors are subtractive. So if I hate math so much, why do I say that this is where the real fun begins? You'll see!

Resonance / Black Magic 101.
Let us assume a circuit with both a resistor, a capacitor and an inductor. We will use small numbers here for simplicity.

If the value of the resistor is 4 ohms, the value of the inductor is 3 ohms, and the value of the capacitor is -3 ohms. (Remember that capacitors are negative in nature). The 3 ohms of capacitive reactance (X C )will negate the 3 ohms of inductive reactance (X L ), and the overall resistance is figured as follows: R Total = R + X L - X C R Total = 4 + ( 3 - 3 ) Whenever a circuit has both inductors and capacitors, there is a given frequency at which X L is mathematically equal, but opposite to X C . In this case, X L is +3 and X C is - 3. When this happens, the Total Resistance is equal to the pure resistance of the resistor, and the capacitor and inductor cancel each other out for all intents and purposes. We say then, that the circuit is in RESONANCE .

When a circuit is resonant, it is at it's lowest point in resistance. Any increase, or decrease in frequency will cause the circuit to have greater resistance.

But because a circuit has less resistance at it resonant frequency, it will allow more of a signal to pass through at resonance than at a higher or lower frequancy than the resonant frequency. The frequency at which the circuit becomes resonant is (for our purposes) completely dependant on the inductance and capacitance of the circuit. The "pure" resistance of the circuit does not affect the resonant frequency of the circuit. Circuits which are resonant at a given frequency are said to be TUNED to that frequency. These are sometimes called TUNED CIRCUITS . They may also be called FILTERS , because they are used to "filter" one set of frequencies apart from all the others within a given band of frequencies. In some circles, tuned or resonant circuits are referred to as TANK CIRCUITS , although I'm not exactly certain why. It has always been my belief that this referred to Tuned Cavities in waveguide, which resemble a tin can or tank in nature. But I have yet to substantiate this idea. Just keep in mind that if you hear someone refer to a tank circuit, they are talking about a tuned filter.

Passive vs. Active Components
As you have figured out by now, there are many different types of electronic components, and you must be familiar with all of these. They all act differently with reference to voltage, current, temperature, pressure, and other outside influences. In order to make learning electronic components easier, they have been divided into two categories: PASSIVE COMPONENTS

and ACTIVE COMPONENTS. While possibly not the best definition, the key difference between active and passive components, is that active components have the ability to produce gain, or amplify a signal, and passive components do not. Some would argue that a component's ability to switch a signal makes it an active component, but I don't see a toggle switch as being active. I may modify this definition later, but for now, this one is enough for you to grasp the concept. So far, all the components we have discussed are resistors, capacitors, and coils. These are passive components. Now we are going to begin learning about active components. Some examples of Active components include Vacuum Tubes, Transistors, Integrated Circuits, etc. We will first study Vacuum tubes, as they are a fundamental building block in the understanding of other active components.

Many "modern" schools today are skipping right over tubes. I plan on EMPHASIZING them, as I see them as a very viable technology. There are new tubes being developed and used every day, because up 'till now, we simply haven't found a device which is more capable of linear amplification at high power and high frequency levels. Some examples would be the klystron, magnetron, Inductive Output Tube (IOT), Travelling Wave Tube (TWT) et al. I'll be willing to bet that you have at LEAST 2 vacuum tube devices that you use on a regular basis in your home right now! Your TV and possibly your computer monitor has a Cathode Ray Tube (CRT). You probably cook meals in a Microwave Oven, which uses a magnetron. And should we, someday, find a way to replicate food or transport people as in "Star Trek", I believe it will be developed using technology similar in nature to vacuum tubes

Vacuum Tubes: A Historical (Hysterical ?) Overview
The vacuum tube, in its very primitive form, evolved from the light bulb. Invented by Thomas A Edison in 1883, the incandescent lamp, had 3 basic necessities to operate: (refer to fig. 1.1) The Envelope The Filament The Vacuum

figure 1.1 The envelope is basically a sealed container, a box or jar so to speak, which completely surrounds (envelopes) whatever is inside. The first envelopes were made of glass, however, there was no written law that they must be made of glass. In fact, many modern tubes have metal and/or ceramic envelopes. The filament, otherwise known as the heater, was the basis of the light bulb. The idea was that if a high enough electrical current flows through a coil of wire, it generates light (and heat). Edison’s object, was to create a thin enough piece of wire, that even a very low current could generate a great amount of light. The problem was that he kept burning up the filaments. They would work for a matter of seconds, then die out. He experimented with many different filament materials. Finally he found a metal material that would last - tungsten. Most modern filaments are made up of a thoriated tungsten material.

The vacuum was added along the way, as an attempt to keep the filament from burning out. It was logical, that in order for fire to exist, you must have oxygen. So Edison assumed that if all the oxygen were removed from the envelope, by creating a vacuum, the filaments would stop burning up. It helped, but was not the total solution to the problem. He did find, however, that if a filament were energised within a vacuum, that after time, a "shadow" would be left on the inside of the glass, which resembled the shape of the filament. He surmised from this, that within a vacuum, particles (we now call them electrons) were emitted around the wire, forming a cloud, or SPACE CHARGE. (refer to fig. 1.2). This effect became known as the EDISON EFFECT, which is the basic operating theory behind all vacuum tubes.

fig 1.2 During his experimentation on the electric light bulb, Edison found that many metallic substances will emit electrons when heated to incandescence. In a light bulb, these emitted electrons become waste, as they serve no useful purpose. The vacuum tube is, however designed to make use of these emitted electrons. Edison experimented by placing a second ELEMENT, or ELECTRODE within the vacuum along with the filament, but not touching it. He then connected an ammeter to the second element, and attatched the other lead of the ammeter to the positive terminal of the battery. He found that when doing this, current would flow through the ammeter. The second element is called the PLATE (refer to fig. 1.3).

fig 1.3 The emitted cloud of electrons, bearing a negative charge, is attracted to the positively charged plate. It flows through the vacuum toward the plate and is collected upon its surface. This action was monitored and proven by use of the ammeter. But what happens if the plate is connected to the negative side of the battery? Edison discovered that when this is done, NO current flows through the ammeter. So electricity flows, within the vacuum, in one direction only from Negative to Positive. This was in direct contradiction to Benjamin Franklin’s conventional theory, that electricity, being a fluid (much like water), flowed from positive (a full glass) to negative (an empty glass). Edison further reasoned that since, with the polarity reversed, the negative particles of electricity didn’t flow from the plate to the filament, that there must be some outside force causing the electrons to leave the filament. He discovered that while he was working with a heated filament, the plate was not heated. The heat of the filament caused the electrons to be "boiled" off, and freed from the solid matter of the filament into the surrounding vacuum. Once the electrons were freed from the confines of the solid matter, they could be attracted to any positively charged source within the vacuum. This is known as THERMONIC EMISSION, which is the process of the electrons being forced out of the solid metal via thermal agitation.

fig 1.3

This is the basic concept of the FLEMING VALVE invented by J. Ambrose Fleming in 1904. It was noted that since electricity flowed within a vacuum tube in one direction only - from the filament to the positively charged plate, it was as if there was a “one way valve” placed in the circuit. By this method, a direct current (DC) charge, formerly only available by chemical production through a battery, could now be converted from an alternating current (AC) source. This outstanding development was called RECTIFICATION and the Fleming Valve was known as a DIODE (two element) RECTIFIER. It wouldn’t be until 44 years later that the crew at Bell Labs would recreate this effect using semiconductor materials.

fig 1.4

The AUDION came about when Lee DeForest, In 1906, added a 3rd element between the two. This third element, a control grid, allowed one to electronically control the output of the tube based directly upon the input. Along with the ability to control the output, came the ability to AMPLIFY the output as well. A small signal could be injected at the input of the tube, resulting in a very large signal at the output of the tube. Electronics was about to take on a whole new role in life, as radio as we know it would now soon be born. The term AUDION was later replaced by the term TRIODE, as the tube has 3 elements within the vacuum. Later improvements included the adding of 2 more elements, the supressor and accelerator grid, which allowed higher frequency operation, increased stability, and eliminated unwanted oscillation. The 4 element tube was called a TETRODE and the 5 element tube was called a PENTODE. The biggest problem in tube design came when trying to reach higher power levels, at higher frequencies. The higher the frequency, the tighter the tolerances became.

In an effort to overcome this problem, the BEAM POWER TUBE was developed. This tube was special, in that it FOCUSED a BEAM of electrons, rather than simply creating a cloud of electrons boiled off the cathode. The beam is focused by applying a sufficiently high negative potential to repel the electrons being boiled off the cathode. At the same time the highly positive plate is attracting the negatively charged electrons. This focused beam of electrons places more energy directly on the plate, eliminating losses, and allowing for better heat distribution.

Even today, in the age of the semiconductor, we can not do without tubes. This

is why I insist that we still study them. They are still (as of the year 2000) used in Televisions, Computer Monitors, Microwave Ovens, Medical Equipment, Radar, Transmitters, and many other phases of high tech electronics. We use some tubes, such as the big red ones pictured above, that are as large as a man. There is also a new wave of "nanotube" technology which might be worth riding. The point is, that tubes are not dead, nor will they be for quite some time, and should be taught as a viable technology. As stated before, this is only meant to be a historical overview. Now we will get into the detailed theory of how each of these tubes operate.

Tube Theory - "ODE" to Electronics
The "Ode to Electronics" would have to be the vacuum tube. This is because you will learn lots of "odes" in tube theory: Electrodes, Diodes, Triodes, Tetrodes, and Pentodes, just to name a few. Before we go too far, we'll have to learn what an electrode is: An Electrode is a conductor which permits current to flow. Remember Frankenstien's Laboratory? It had the two round balls with the high voltage applied, and you saw the electricity arcing across from one ball to the other? These were electrodes, and they allowed current to flow from one ball to the other through the air. Electrodes are always used in pairs. You could say that the big alligator clamps on your automobiles jumper cables are electrodes, as are the little pads the doctor puts on your chest when he hooks you up to an EKG. Although I'd rather that the doctor use the little pads than the jumper cables! In tubes, the electrodes are elements within the vacuum which emit, collect or control the flow of current within the tube.

The simplest of tubes has only 2 elements: The Cathode, and the Anode.

Looking at the pictures above, the picture on the left is a graphical representation of a "diode" or 2 element tube. It has a CATHODE (K), which emits electrons, and an ANODE (A), otherwise known as a PLATE (P), which collects the emitted electrons, allowing current to flow. The picture on the right is a schematic representation of the same. The circle represents the glass envelope, and the elements are contained within. The Cathode shown here looks like an inverted "V", and the Plate looks like, well, a flat "plate" of metal. What you see in the schematic on the right above is actually two circuits combined. We will now break these two circuits down, to simplify and show what is happening in each circuit. Keep in mind that there are multiple theories on the flow of electricity. We will use the electron theory (negative to positive) first to describe how current flows through the tube. However, whenever describing how power gets to the tube, it may sometimes be easier to think in terms of conventional flow from positive to negative. In the schematic to the left, arrows show the flow of electrons from the negative battery terminal, through the cathode of the tube, and back to the positive terminal of the battery to complete the circuit. The cathode gets red hot and glows. It gets so hot, that some of the electrons are thermonically emitted into the

vacuum space directly around it, as shown by the little specks in the picture. The Cathode, in this case, is directly heated by the high flow of electron current through it. An electrode which is directly heated in this manner is also called a heater or filament. Not all filaments or heaters are cathodes, and not all cathodes are heaters or filaments. When a cathode is DIRECTLY heated, as this one is, then it is a heater / filament / cathode. Otherwise, tubes may have seperate heaters & cathodes, in which case we say the cathode is INDIRECTLY heated. Below are illustrations of both types of cathodes, so that you may understand them better.

As you can see from the schematic diagram, the circuit operates in the same manner, except the heater is seperate from the cathode. This is done for several reasons, including increased reliability and longer life, less interference between signal and power supply stages, lower resistance, higher frequencies can be obtained, and ease of design. Understanding the left side of the schematic gives us some insight to what happens when we apply voltage to the plate. By applying a positive voltage to the plate, a current can be observed on the Current Meter ( also called an Ammeter ), indicating that the circuit is complete between the two terminals of the battery. So by the indication of current flow on the Ammeter, we can assume

that there is a complete loop formed via the plate! The electrons leave the negative side of the battery, and are emitted by the cathode of the tube. They are then collected by the anode (plate) and returned to the positive side of the battery. Edison noted that if the polarity of this battery is reversed, so that a negative voltage is applied to the plate, no current flowed. It was surmised from this, that current only flows in one direction within a vacuum - from negative to positive.

Tube Theory - The Diode

Both of the schematics above show the operation of a diode tube. Now let's study a little about the theory of it's use. While not the only use for a diode, the most common use is that of RECTIFICATION . Rectification is just a big fancy word for changing Alternating Current into Direct Current. A RECTIFIER turns AC into DC, and a diode is an excellent rectifier.

This is because it only allows electrical current to pass through the plate circuit in one direction. Let us examine what happens when we apply an alternating current to the plate circuit. We replace the battery in the plate circuit with an AC generator. The AC generator creates electrical voltage which swings from a positive to a negative potential each cycle. When the generator's terminal on the cathode side swings negative, the the one on the plate side swings positive. This energises the tube such that the cathode is negative and the plate is positive. The electrons floating about in the electron cloud are repelled by the negative cathode. At the same time, they are attracted to the positive potential of the plate. For this reason, they travel through the vacuum to the plate. These electrons then go through the Ammeter, making it read current flow, and continue onward to the load resistor. Finally they reach the most positive point in the circuit - the positive terminal of the battery. They are drawn to the positive, much like a South pole magnet is drawn to a North pole magnet, and they will move toward each other until they meet. When, however, the AC generator reverses (alternates) it's polarity, such that the generator's cathode side terminal swings positive, and the plate side swings negative - look what happens !! With the cathode being positive, the electron cloud collapses, and no electrons are present to cross over to the plate. Because the plate is not heated to thermonic emission, it does not radiate electrons, and so will not allow current to flow. Current flow stops at the plate. Therefore, in a vacuum tube, ELECTRICITY CAN ONLY FLOW IN ONE DIRECTION

If we draw a graph, indicating voltages fed to the cathode vs current flow monitored at the plate, we will see a pattern. Electricity only flows on the positive cycle of the AC waveform. While the input swings both positive and negative, the output fluctuates from 0 volts to some positive number of volts. In effect, the input is Alternating between positive and negative (AC) but the output is positive only (DC). We say that the output of the tube has been rectified. It is, however pulses of DC, and for most general purposes, useless until we clean it up. This IS however, the basis of EVERY POWER SUPPLY in every piece of electronic equipment you own. The Characteristic Curve of the diode is found by applying several different voltage levels, and measuring plate voltages vs. plate current. We note that below a certain plate voltage, ( in this case 0 volts ) no plate current flows. The minimum point at which the tube no longer operates is called the CUTOFF POINT . Above a certain plate voltage, additional plate voltage has very little effect in increasing the plate current. The maximum point where raising the plate voltage no longer increases current is called the SATURATION POINT .

Dangerous Curves
As discussed in the previous lesson, a Characteristic Curve is found by applying several different voltage levels, and measuring plate voltages vs. plate current. We note that in a diode, if we go below a certain plate voltage, ( in this case 0 volts ) no plate current flows. The minimum point at which the tube no

longer operates is called the CUTOFF POINT . Above a certain plate voltage, additional plate voltage has very little effect in increasing the plate current. The maximum point where raising the plate voltage no longer increases current is called the SATURATION POINT . In reality, there are two different factors involved in the control of the amplitude ( or level ) of the plate current that flows in a diode. These are the filament voltage ( sometimes called the heater voltage ), and the plate voltage. Remember that the cathode must be HEATED into thermonic emission. The temperature of the cathode must be high enough to "boil" the electrons from it's surface. It stands to reason, that the higher the temperature we heat the cathode to, the more electrons will be "boiled off". Much like raising the temperature of a pan of water causes it to boil away into steam faster. ADVANCED CONCEPT There does come a point though, where we can boil the electrons off no faster. As we raise the voltage on the heater, it will actually begin to slow down the movement of electrons toward the plate, and begin drawing them toward the heater itself. Therefore, when setting up a tube for operation, you want to make sure that you don't set the filament voltage of the tube so high that it will cause this effect, as it will reduce the efficiency, as well as the life expectancy of the tube. Most tubes are operated at standard values of 6 or 12 Volts. Often, if a tube gets weak, you can boost, say a 6 Volt filament to run as high as 7.5 or 8 Volts. This may extend the life of the tube for a while, but you must watch the plate current. If plate current begins to drop off, then you have the filament voltage set too high. It is usually considered standard practice to run a tube at the lowest filament voltage that will make the current necessary for proper operation of the device. This maximizes the life expectancy of the tube. END OF ADVANCED CONCEPT Assuming that the filament voltage of the tube is set, we can increase the plate current by increasing the plate voltage. Normally when plotting ( or drawing ) an operational curve for a tube, we assume that the filament is held constant, and the plate voltage is raised. As the plate

voltage rises, so does the plate current. We do note, however, that there is a minimum and maximum point, at which the curve is no longer linear ( in a straight line ). We call the minimum point the "lower knee" and the maximum point the "upper knee" of the curve. The saturation point occurs at the beginning of the upper knee, while the cut-off point occurs at the beginning of the lower knee. Under normal conditions, we usually operate the tube within the linear portion of the curve. Later, we will discuss the characteristic curves of various other components. Each type of component has a slightly different curve, which dictates how the component will operate under different conditions. Understanding these curves will give you a more thorough knowledge of how the component works, and insight as to what it will do when it fails.

Lesson 41 - A Short Review
Thomas Edison, famous (at least in America), for inventing the light bulb, made many discoveries before he completed his task of lighting the path of the world. Along the way, he incidentally noted that if a filament were energized within a vacuum, that after time, a "shadow" would be left on the inside of the glass, which resembled the shape of the filament. He surmised from this, that within a vacuum, particles (we now call them electrons) were emitted around the wire, forming a cloud, or SPACE CHARGE. This effect became known as the EDISON EFFECT, which is the basic operating theory behind all vacuum tubes. Later, J. Ambrose Fleming invented the FLEMING VALVE, when he noticed that a second ELEMENT, or ELECTRODE within the vacuum along with the filament, but not touching it, electricity would flow through the vacuum and be collected on the second element. The second element was called a PLATE. He further noted that electricity would flow from the filament to the plate, but not in the opposite direction. The Fleming valve was later dubbed the DIODE, because it has 2 elements inside the vacuum - the filament and the plate. The AUDION came about when Lee DeForest, In 1906, added a 3rd element between the two. This third element, a control grid, allowed one to electronically control the output of the tube based directly upon

the input. This was the birth of Amplification. The term AUDION was later replaced by the term TRIODE, as the tube has 3 elements within the vacuum. The reason why a tube works is because the CATHODE is heated to a point of THERMONIC EMISSION, forming a SPACE CHARGE or cloud of electrons, which is attracted to the positive charge on the PLATE or ANODE. The Cathode ( K ) of a tube can be either directly or indirectly heated. Diode tubes only allow electrical current to flow in one direction. By using a diode tube we can change, or RECTIFY, Alternating Current into Direct Current. An X / Y plot of Voltage vs. Current produces the CHARACTERISTIC CURVE of a device. We looked briefly at the characteristic curve of a DIODE tube. Now let's look, for a moment, at the curve for a resistor. Remember on page 8, we discussed Ohm's law. We used a 10 Ω resistor for an example. When we applied a 100 volt source to the resistor, 10 Amps would flow through it. What happens, though, if we reduce the voltage to 10 volts?

10 Volts / 10 Ω = 50 Volts / 10 Ω =

Click for Answer

Now let's try another voltage value.

Click for Answer

Finally, what happens if we apply a Zero volt source to the resistor?

0 Volts / 10 Ω =

Click for Answer

If we plot this change on a chart, we will find that a resistor has a characteristic curve which equals a straight line. Not all resistors will be an exact 45º angle. The angle of the line will depend on the value of the resistor. However the characteristic curve of all resistors will be a straight line if plotted voltage vs. current.

Lesson 42 - The TRY - ode

Up to now, you have learned something about the diode vacuum tube and how it works. The most important point to rember about the diode is that it only allows current to flow IN ONE DIRECTION. Thus, when a diode is connected in series with other circuit components, current can flow in only one dirction in all of these components. This characteristic makes the diode a useful device for "rectifying", or converting AC into DC.

You have learned that the diode vacuum tube has only 2 electrodes - a cathode, and a plate (or anode). We briefly hinted that there were other types of tubes tried over the years, with more electrodes added. In 1906, Lee DeForest developed the Audion, later called the Triode because it had 3 electrodes The third electrode, called the Grid, was placed between the cathode and the plate. The Grid was a piece of wire mesh, coil, perferated metal, or other shape that would allow electrons to pass through it. Physically, the Grid is much closer to the cathode than it is to the plate. The purpose of the Grid, is to offer a way to control the flow of electrons to the plate. For this reason, the Grid is sometimes referred to as the "Control Grid". The question you are probably asking at this point is, "How does it work?" During normal operation, the Plate is kept at a Positive DC potential in relation to the Cathode, so that it always attracts electrons. ( memory note: P = P.... Plate = Positive). The Negative electrons being boiled off the Cathode, are attracted to the Positive plate, and begin to flow in that direction. The more Positive the Plate is, the greater the attraction, and the more electrons flow. We will assume, however, for the sake of our discussion, that we have a fixed high

Positive voltage on the plate, and a fixed Negative voltage on the Cathode. We have current flowing from the Cathode to the Plate at a fixed rate. Now we apply a voltage to the Grid. If we apply a small Positive voltage, electrons flow from the cathode toward the grid. Since the Grid voltage is small, and the Plate voltage is large, the electrons continue past the Grid on to the Plate. The Grid, being closer to the Cathode than the Plate is, gets the electrons moving in the direction of the Plate, and sort of helps them along their way. Because of this, more current flows to the Plate with a Positive Grid than with an un-energized Grid or no Grid at all. If, however, we apply a Negative voltage to the grid, it creates a Negative field between the Cathode and the Plate. This field restricts the flow of electrons moving to the plate. Sort of like pinching a garden hose. The tighter we pinch it, the less water flow there is. The same is with the Control Grid of an electron tube. The more Negative we swing the grid, the less current flows at the plate. So we find, then, that when the Grid Voltage swings Positive, Current flow is increased at the Plate, and when the Grid Voltage swings Negative, the Current flow is decreased at the Plate. Speaking "mathematically", we would say that the "Grid Voltage is directly proportional to the Plate Current ". In plain english, we can say that we can control the CURRENT of the PLATE, by changing the VOLTAGE of the GRID. So then, what happens when we apply an ALTERNATING current to the grid? If we place an AC signal on the Control Grid of a triode, the signal swings from Positive, to Negative, then back to Positive. As it does so, the Plate Current swings directly with the Grid Voltage. If we have a fixed resistance load ( a resistor ) across the output of the Plate, we will notice that when the Plate Current goes High, the Plate Voltage goes Low. As the Plate Current goes Low, the Plate Voltage goes High. ( Ohms Law applies ... E=IR ).

So if we compare, when the GRID Voltage swings High.... the PLATE Voltage swings Low. The Voltage at the Plate swings OPPOSITE the voltage of the Grid. The Output of the Plate will look like a mirror image of the Input to the Grid.

Lesson 43 - The Triode as Applied to a Circuit
Knowing what a diode is, or how a triode works is of little use unless you have some practical knowledge of how it can be applied within a circuit. We are going to begin with a VERY basic schematic of an early transmitter. Do NOT try to build this at home! It probably won't work, and you may violate Federal Laws ( FCC regulations ) or injure yourself in the process. I will let you know when it is time to begin building projects. ( Yes, this course will come with a practicum ). I will also begin to explain the theory and operation of some new components.

When ever we are looking at a schematic diagram, we must look at it from 2 directions. Top to Bottom, and Left to Right: First: No circuit can operate without some kind of Power, In this schematic, we have 2 batteries shown operating the circuit. While it may* be true that electrons flow from negative to positive, it is usually easier to understand movement of power through a circuit using the Conventional current flow theory, otherwise known as the Franklin theory, which states that electricity flows from positive to negative. When looking at a schematic, it is customary to start with the highest positive voltage, which is normally at the top of the diagram, and work your way down to the lowest voltage, usually ground, which is located at the bottom of the diagram. Second: The purpose of most circuits is to move some kind of signal. Signal flow normally goes from Left to Right. Signals can be anything from basic AC sine waves, to audio, video, radio, or data signals. They normall begin with some signal source on the left, and move to the right. Before you can fully understand the circuit, I will have to give you a brief introduction to microphone construction and theory.

In the following illustration, I show a breakdown of how 3 different types of microphones work. In all three types, when we speak into the microphone, the sound waves from your voice create vibrations in the air. When these sound waves reach the microphone, they vibrate the diaphram of the microphone, which is usually a very thin layer of flexible plastic. This diaphram works like the eardrum in your ear, and vibrates back and forth at the same frequency ( pitch ) and amplitude ( volume level ) of the sound waves that stimulate it. The diaphram in all three types move left and right as shown. The third pictures a 3 dimensional representation of a magnetic type microphone for ease of understanding. In the case of the Condenser type, a condenser is basically a capacitor. Here we have 2 electrodes, separated by an air dialectric. When the diaphram moves, it moves one of the plates, which changes the distance between the plates. Since the distance between the plates governs the capacitance of a capacitor, by moving one plate, we change the capacitance of the capacitor. The changes in capacitance are directly proportional to the frequency and amplitude of the sound waves picked up by the diaphram. So the electrical signal coming out of the microphone reflects the sound waves picked up by the diaphram. Carbon microphones work in similar fashion to Condensor microphones, except that instead of an air dialectric, we have carbon, which when compressed, changes its resistance instead of its capacitance. In short, we have a variable resistor, which changes reflect the incoming sound. Finally, a dynamic, or magnetic microphone has a moving coil, which is moved by the diaphram when it vibrates. The hair like strands of wire in the coil move back and forth with the incoming sound, cutting the magnetic field of the permanent magnet. As you recall, when a wire cuts the field of a magnet, an electrical current is induced in the wire. When the coil moves, it generates a

small electric current, which changes with the incoming sound. Many microphones, such as the Carbon and Condenser type require power, whether via battery or "phantom power" to operate. Because a Dynamic microphone actually generates an AC current, it needs no outside power source.

Now let's get back to our diagram. Here we actually have 3 circuits. Let's begin with the first, and simplest, which I hope will allow you to get the idea of how to read a schematic diagram. On the far left of the diagram is this small section, which includes 3 components. There is a microphone on the left, a coil on the right and a battery at the bottom. The battery provides power for the microphone to operate. The positive side of the battery is connected to the microphone directly. The negative side passes DC current through the coil to the other side of the microphone. Think of the microphone as a very thin membraned capacitor, with air acting as a dilectric. As we speak into the microphone, the vibration of the sound waves from our voice generates an alternating current, which varies directly in amplitude ( volume level )and frequency ( pitch ) with the changes of our voice. This alternating current is applied to the coil, causing it to set up an induced electromagnetic field, which rises and colapses, changing along with our speach. Now on to the second part of the circuit... the Tube Amplifier! First let's go over power, then signal. The tube, being the active device in this circuit, is

powered by the battery. The Positive side of the battery produces a positive voltage, which passes through the plate coil to the PLATE of the Tube. The Plate, having a positive potential, is ready to begin attracting electrons. We'll say we have a BIG battery, and it puts out 200 Volts. The CATHODE of the tube is directly connected to the negative side of the battery, and begins to emit an electron cloud, which is attracted to and caught by the PLATE. We now have a flow of current from CATHODE to PLATE. Note that on the bottom right hand corner of our diagram we have another symbol ( 3 horizontal lines gradually getting smaller ). This is the symbol for the "ground" potential of the chassis, and is usually considered to be "0 Volts". ADVANCED CONCEPT Now at this point, you might ask, "What is the voltage on the Control Grid?" This would be a very good question. Because of the combined resistances of the grid coil and grid resister, the grid must be at some voltage higher than that of the cathode. So if we say that the Plate is at 200 Volts, and the Cathode is at 0 volts, the grid must be somewhere in between. Another way of saying this is that the grid is positive with respect to the cathode. But because a coil has very little resistance at DC (battery), it wouldn't be TOO much higher than the 0 Volt Anode voltage. We'll estimate and say 1 or 2 volts. END OF ADVANCED CONCEPT Now we have 2 more terms to learn: We now can say that the tube is working, but it is just sort of idling along, sort of like a car sitting at a traffic light. The motor is running, but it isn't going anywhere. When a tube has the proper voltages to operate, we say that it is "properly biased", and BIAS means voltage in most electronics work. Also, whenever a tube is running, but in an idle state, with no signal applied, we say that it is in it's QUIESCENT state. ( think "quiet" ). Now let's apply a signal and see what happens. The signal from the microphone circuit is magnetically coupled to the amplifier circuit by way of 2 coils - the microphone coil, and the grid coil.

The mike coil is physically placed very close to the grid coil. When two coils are so close, that the magnetic field from the first coil is induced upon the second coil, we have what is called a TRANSFORMER. Often 2 coils are actually wound on the same coil form. These coil forms can have an air dilectric, or may be ferrite ( iron ) based, which increases the amount of energy transferred from one coil to the other. With a signal applied across the grid coil, it travels along the wire to the grid. The signal voltage alters the grid voltage at the rate of frequency and amplitude that is picked up by the microphone. This in turn increases and decreases the current which moves from the anode to the plate of the tube as described in the previous section. The output from the tube is an exact replica of the input of the microphone, except that it is greatly amplified ( made louder ), and is flipped to look like a mirror image. So now that we have an amplified signal, what are the other components in the circuit for? Let's go over them one by one: The Grid Biasing Resistor: The grid resistor sets the bias voltage for the grid, so that it never reaches the two taboo states - cutoff and saturation. When a tube is in cutoff, it doesn't have current flow from anode to plate. When it is saturation, any change in signal at the grid won't be seen at the plate, because it will be at maximum current flow constantly. Both of these conditions can cause distortion of the signal, and are usually* unwanted. It is for this reason that we need to control the bias voltage to the grid by using a grid bias resistor. The Plate Coil: Why didn't we simply connect the positive terminal of the battery directly to the plate? Answer: Because the output signal of the tube would then affect the battery current, which would affect the battery voltage, which would affect the tube operation. Bad Scene! Recall that a coil PASSES low frequencies ( D. C. is about as low as you can get ), but blocks the affects of AC. By using a plate coil, we can freely pass the DC to bias the plate, without the output signal affecting our power supply. The Plate Coupling Capacitor: The purpose of this guy is simply to block the DC from the power supply from getting into the next circuit, while allowing the AC signal to pass on. Hence, it is called a "coupling capacitor", because it couples 2 circuits together.

After the coupling capacitor, we have the final output section of our transmitter. In the output section, there is a radio frequency signal generator, a transformer, and an antenna. Our amplified audio signal is coupled to the "final" section by way of the coupling capacitor. It then goes into the antenna output transformer. On the other side of the transformer is our radio frequency generator. The radio frequency generator creates a radio signal ( we won't go into how just yet ), which is coupled across the transformer to the audio side. The two signals mix in the transformer, and are sent out the antenna into the atmosphere. Now let's review:

Lesson 44 - Circuits Circuits Everywhere!
In the last section, we saw how a very simple transmitter worked. It was made up of several different types of electronic components, including capacitors, transistors, resistors, etc. When we assemble several types of electronic components in a configuration that serves some purpose, we call it a CIRCUIT. Some common electronic components are: Wire Resistors Capacitors Coils Transformers Tubes Transistors Diodes All circuits are combinations of individual electronic components assembled to perform a function. The "type" of circuit it is, depends on the function of the circuit. We have already discussed some simple circuits, called "filters", and have also gone through "power supplies". Now we have introduced you to "amplifiers". Here is a list of some of the major types of circuits we will discuss and explain how they operate: Power Supplies Filters Amplifiers

Oscillators Mixers Logic Circuits Almost any device or type of electrical equipment is made up of a COMBINATION of these circuits.

Our transmitter, for instance, is an Audio Amplifier, which drives an RF Mixer, which has a second input from the RF Oscillator (High Frequency Generator). The Mixer combines the inputs from the Audio Amp and the Oscillator to create a radio signal that is modulated by the audio signal, which then goes out to the antenna. Of course this is an over simplification of what really has to happen, but the point is, that it is ALL done by basic circuits, and that if you learn and understand the simple circuits, you can look at VERY complex devices, and understand how they work! We need to discuss each of the basic types of circuits in greater detail until you fully comprehend the theory behind how they work. Then you will have a firm grasp on electronics, and can begin combining them to create useful circuits. First, let's cover the two electronic components we haven't covered yet: Transistors and Diodes.

Lesson 45 - Semiconductors - Diodes and Transistors
But we've already discussed diodes. They are a simple form of vacuum tube aren't they? Well - yes and no. While diodes existed in tube form for many years vacuum tube diodes had their problems, and the electronics industry would try to find a way around those problems. Vacuum tube diodes did a fine job of rectifying (turning ac into dc), but they wasted a lot of electrical energy in the process, which made them inefficient and costly to operate. Quite a bit of power was lost just keeping the filament warm! They also had the problem of being physically fragile, and tended to be the main cause of an electrical equipment failure. As early as 1874, researchers noted that a metal-lead sulfide junction had rectifying properties. They found that it would conduct electrical current in one direction, but if they reversed the current, it would not flow in the opposite direction. This "junction" was "semi-conductive" in nature. They had, without knowing it, invented the semi-conductor. The problem was, they had no practical application for it, and to be honest, didn't understand how it worked. However, In 1926, P.H. Geiger and L.O. Grondahl discovered the rectifying properties in a semiconducting copper oxide-copper junction. Armed with W. Schottky's theoretical explanation of how it worked, this was the first practical diode that didn't involve a vacuum tube. Other materials that involved semi-conductive junctions included silicon, germanium, and selenium. On Tuesday, December 16, 1947, Physicists John Bardeen and Walter Brattain, while working for William B. Shockley at Bell Labsoratories, invented the semiconductor transistor. With the single statement "This thing's got gain!", Brattain anounced the discovery of a SOLID-STATE device that could actually amplify electrical current!. By 1956 Bardeen, Shockley, and Brattain, shared the Nobel Prize for jointly inventing the transistor. It was a grand time for the electronics industry. The invention of the transistor would mean the dissapearance of the tube... or would it? Still to this day, there are applications where the transistor isn't practical. Tubes tend to work better for high power or high frequency applications. It is a tube that you look at on your computer monitor (CRT = Cathode Ray Tube). Your TV set and microwave ovens employ tube technology. Most Television Transmitters use a tube as their final output stage. "Nanotubes" are the latest craze in electronic inovation. Audiophiles swear by the rich, full, warm, reproductive sound that can only tubes can make in audio circuits. It is my belief that we need to further understand both tube and transistor technologies, and use them in tandom. It is for this reason that I taught tubes first, and that I

will emphasize them throughout the rest of the course. But now let's take a look at semiconductors:

Lesson 46 - The Basics of Semiconductive Materials
*Note: This course is NOT intended to teach chemistry or solid state physics, but to give just enough background for a 6th grade student to understand semiconductors. For a slightly more in depth look at how semiconductors work on a submolecular level, check out this web page: SEMICONDUCTORS

Without going into complete details of how a semiconductor works, there are certain things we must know about them in order to use them. Semiconductors are chemical elements, that when compounded with other elements, have certain electrical characteristics.

¿what? There are several types of Semiconductive chemicals, to include but not limited to, Silicon, Germanium, Selenium, and Copper Oxide. Semiconductors do not normally conduct electrical current. But when they are combined with other chemicals, like Boron or Arsenic, can be made to partially conduct. When we combine the second chemical to the semiconductive chemical, we say that the semiconductor is "doped". Doping can either be negative doping, or positive doping. The real magic occurs, though, when we put the two types together. In the diagram to the right, we see a device with both a positively and negatively doped section joined. The point at which the two sections join, we will call the N - P junction ( or simply the junction ). Think of the junction as a hill, and the electrons flowing through it as a ball. As long as the ball is rolling down hill, it is easy to push along. But try pushing the ball uphill, and it is much harder to do. The same goes with the flow of electricity through a junction of P and N doped semiconductor material.

Consider, for a moment, what happens if we connect a negative DC voltage to the N doped side, and a positive DC voltage to the P doped side. According to the electron theory of current flow, electrons move from negative to positive. The electrons leave from the negative side of the battery, moving toward the positive. They come into contact with the diode, which acts like a "hill" to the electrons. The electrons flow "downhill", and current flows easily. But what happens if we reverse the direction of current flow by reversing the battery?

If the battery is reveresed, the polarity applied to the diode also changes. Electrons still try to flow from negative to positive, however, going through the diode, is more like rolling a ball uphill. It takes much more effort to push the ball uphill. The hill is steepest at the point of the P - N Junction, where it is nearly impossible to push the ball up the hill.

Because of this, a semiconductor diode acts much like a vacuum tube diode, as it conducts in one direction, while having a high resistance to current flow in the opposite direction. It is possible, however, to make a diode conduct electricity in reverse. If a high enough voltage is applied across the junction ( which is also sometimes called the "depletion region" ), it will conduct in the reverse direction. Just like if you kick the ball hard enough, it will eventually go over the top of the hill. However, when this happens, the diode is no longer acting quite like a normal diode. Some diodes are actually designed to be operated in this manner. These are called " ZENER DIODES ". When an exact given reverse bias voltage ( 12 Volts for instance ) is reached, the junction of the diode begins to " break down ", and act like a piece of wire. It does not conduct electricity only in one direction, but in both directions at this point. The semiconductor diode ( usually just called a " diode " ), is one of the most important building blocks of modern electronics. To the right is a picture and the schematic symbol for the diode. Note that there is always a line, or band that circles around one end of the diode. This line indicates which end of the diode the cathode, or positive end is on. Sometimes instead of a line, there is a dot or some other kind of indicating marker, but the cathode is always indicated, as the proper polarity of a diode is crucial in a circuit.

Lesson 47 - Transistors

Recall that in a semiconductor diode, we have 2 regions of DOPED semiconductive material. One region is doped positive, and the other region is doped negative. There is also a junction, where the two regions are joined. When a diode is forward biased, it conducts electricity easily, like a ball rolling down a hill. When it is reverse biased, it is extremely resistive to current flow, as the ball is rolling uphill, and is much harder to get over the hump. Remember also, that we had diode tubes, which operated in a similar manner. They would conduct electricity in one direction easily, but would not conduct in the opposite direction. When we added another element to a tube, we created a triode, which would not only allow electricity to flow, but could also amplify the signal. Reason tells us that if we add another element to a semiconductor diode, that a similar effect should take place. In December of 1947, Scientists at Bell Laboratories would prove this theory correct. With the addition of a 3rd semiconductive layer, joined at a second P-N junction, W. H. Brattain made the world famous comment, " We've Got Gain! " implying that this 3 layer device could amplify! With proper bias applied, there is a small hill to overcome at the first P-N junction (aproximately 0.7 Volts for Silicon, 0.3 Volts Germanium), which is the normal charactaristic for any semiconductor diode. But then the electrons reach the peak of the hill at the second P-N junction, and have a fast run downward. There is an increase in flow downhill, and the electrons act like a waterfall, pouring into the collector. It may seem at first, that a transistor is like 2 diodes placed back to back, an in resistance checks will even resemble this. Actually though, 2 diodes back to back will not operate like a transistor in circuit. A diode only has 2 semiconductive regions, and therefore has 2 leads. A transistor, on the other hand, has 3 regions, and must have 3 leads. To the left is a photo of a small signal transistor. Just as you must know which end is which on a diode, a transistor has markings which identify which lead is which. The three leads are called the Emitter, Base, and Collector. The Emitter is the lead that current enters into. It can be

compared to the Cathode of a tube. The Collector is the lead that current exits from. It can be compared to the Plate of a tube. Finally, the Base is the controlling lead, and is comparable to the Control Grid of a tube. It might help to remember that electrons are emitted at the Emitter, collected at the Collector, and controled by the Base. Transistors come in many different packages, and while they are always marked so that you will know which lead is which, they are by no means standard. One transistor may have the emitter on the left, another may have it in the middle. Transistors do, however have identifying marks, and can be referenced to find out which lead is which. Of the many kinds of transistors there are, probably the most commonly used is the Small Signal, Bipolar transistor, as pictured above. Bipolar transistors come in two flavors: PNP and NPN. This is because the semiconductive material can be laid out in ( basically ) two different ways. If we look closely at how a bipolar transistor is made, we can understand more easily how this can be. The illustration to the left is a cutaway of a semiconductor transistor. Try to visualize this as being circular ( button shaped ) from the top view, with 3 layers, one upon another. Transistors are built in layers by very precise machines. Each layer is added to the layer below it. We begin with a single layer ( or substrate ), and add layers on top of it. If we begin with a layer of N type semiconductor ( on the bottom ), the second layer would be P type, followed by another N type. We say that transistors, and other semiconductive devices, are "grown" in this manner. The second layer ( in this case a P type ), is very thin, along the order of 800 micrometers ( μM ) or less. As shown by the blue line, electric current enters via the N type emitter substrate layer, passes through the ( red ) P type base substrate layer, until it reaches the N type collector substrate layer. The gold colored lines represent the leads that connect the transistor to outside circuitry. If we were to reverse the N and P layers, we would have a PNP transistor, with the base being N type, and the emitter and collector being P type material.

The schematic diagram symbol for a bipolar transistor is shown to thre right. Notice that the only difference between an NPN and PNP type transistor, is the direction of the arrow. To remember which is which, just keep in mind that the NPN is Not Pointing to the base. ( NP = Not Pointing ) Otherwise, the two symbols are identical. The EMITTER is ALWAYS the ARROW, the base is always the line ( think baseline ), and the collector is the one left over.

Rules for Bias Connections
This is important! Pay Attention!! The Emitter - Base connection is always FORWARD biased. This means more Positive to P type & more Negative to N type. Also, for a Silicon transistor, there must be at least a 0.7 Volt DC bias across the emitter-base junction in order for the transistor to be active. Many times, when without a schematic, I have been able to repair a circuit simply by looking for 0.7 VDC across the E-B of every transistor in the circuit. If it doesn't have at least 0.7 V across it, it isn't turned on! Of course, the bias is 0.3 Volts DC for Germanium Transistors. The Collector - Base connection is always REVERSE biased. This means more Positive goes to N type & more Negative goes to P type. You must be wondering now, how the Collector-Base junction can be reverse biased while the Emitter - Base junction is forward biased? The answer lies in the words "More Positive" and "More Negative". You see, electronics is more of a relative science than an exact science. Is 5 Volts D.C. positive or negative? Well, it's more positive than 2 Volts D.C., but less positive than 9 Volts D.C. Did I lose you yet? It's simple. Let's try plotting it out on a number line: Assuming a Silicon NPN transistor: We know that the the Emitter-Base junction must be

FORWARD biased (Positive to P type doping & Negative to N type doping). So the Emitter must be more Negative and the Base must be more Positive. We know then, that the Base must be 0.7 Volts ( minimum ) Higher than the emitter. So if, say, the Emitter is at 3 Volts, ( I just picked that number at random). We plot 3 Volts on the number line. If the Base has to be 0.7 volts Higher than the Emitter, then the base has to be at least 3.7 Volts. ( 3 + .7 = 3.7 ) So we plot that on the number line. So far so good! Now comes the tricky part. In a NPN transistor, the Base is P type doping, while the collector is N type. But we want it to be REVERSE biased ( Positive to N & Negative to P ), so we want the N doped collector to be MORE POSITIVE than the P doped Base, which is at 3.7 Volts. So any voltage above 3.7 would work. Let's say, 5 Volts. ( We plot that on the number line ). So in order to turn on this NPN trasistor, we would need the following voltages: Emitter = 3.0 Volts Base = 3.7 Volts Collector = 5.0 Volts. This is why, in the picture above, I have a minus sign ( - ) next to the base, a plus sign ( + ) next to the base, and TWO plus signs ( ++ ) next to the collector. It demonstrates the relative polarity of each terminal. We have a pattern then, that while it is an NPN transistor, it is biased N-P-PP, with the COLLECTOR being the MOST POSITIVE point. If we go through the same logic for the PNP transistor, we would find that it needs to be biased P-N-NN, with the COLLECTOR being the MOST NEGATIVE point.

Lesson 48 - Biasing & Class of Amplification

Back in lesson 44, we hinted that all the circuits you will come across in electronics are made up of a combination of simple circuits. These simple circuits are: Power Supplies Filters Amplifiers Oscillators Mixers Logic Circuits Almost any device or type of electrical equipment is made up of a COMBINATION of these circuits. With lesson 48, we will begin to examine these circuits in detail, using both Tubes and Transistors - as you may come across either one in your career. To be honest, most of you unfortunate folks will never have the opportunity to work with tubes. I suggest that if you ever get the chance - take it. It is very rewarding. While there are certain advantages to transistors, there are also advantages to tubes - the least of all is a better, more full understanding of electronics in general. That being said - Let's discuss Power Supplies. The purpose of the power supply is to provide constant power to a circuit for proper operation. Power comes in two basic varieties - AC and DC. You know by now that AC stands for Alternating Current - much like that which comes out of the wall. DC stands for Direct Current, like what comes out of a battery. Equipment which runs off AC may use the raw power from the wall, or it may convert it to a different voltage. You may run into AC-to-DC converters, as well as DC-to-AC converters. There are even power supplies (you might have one in your home) which convert AC to DC, then DC back to AC. Why would you want to do that? Example - an uninterruptable power supply - otherwise known as a UPS. It takes power from the wall, and converts it to DC battery power. Your computer works of AC house power - but you don't want it to die if there is a power outage. So you put a UPS in line with it. If the power fails, your computer keeps working, because it is running off the batteries in the UPS. But the batteries are charged daily by the house power. So we convert AC to DC then back to AC. So what exactly is a power supply made of? Typically, it is a combination

of diodes, capacitors, coils and resistors. There may be more involved - but we'll get to that. Most electronic equipment actually works off DC power. This is because it is easier to control the quiescent biasing of an amplifier, or set the control point of a switch, if you begin with known DC voltages. The problem is that most power sources are AC. So somehow - we have to start with Alternating Current, of whatever voltage, and convert it to Direct Current. We've already discussed this in some minor detail - let's get dirty now, shall we? First - let's look at AC power systems. While I can't go through the specs for EVERY country, I'll go through the specs for the United States as an example, and if you are from another country, you can look up the power codes for your particular country - consider this your homework. For a more detailed version of how this works, you may go to http://www.osha.gov/SLTC/etools/electric_power/illustrated_glossary/inde x.html But basically, it works like this: Power comes out of the power generation plant at 20,000 volts. It is then transformed with a step up transformer at a transmission station to 345,000 Volts. It is stepped up to this high voltage, because at higher currents, it would require larger diameter wire to carry the current. By running high voltage, lower current - they can use less expensive wire and have lower resistive losses. One key thing to keep in mind when looking up at power lines is - the higher up in the air they are - the higher the voltage they carry. This 345,000 Volts (345KV) lines take the power to subsequent sub-stations, where the voltage is stepped down to suit the customer's needs:

The power comes into the customer's building as 4000, 480,440,240, 220,208,or 120 Volts. 120 and 240 are typically single phase lines like you have in your home. On the other hand, the other voltages are three phase,

either in a Wye or Delta configuration. Don't worry about these terms in detail at this time. The important thing to know is that each of these various powers come into the building being stepped down from a higher voltage by a transformer. Transformers, as we have discussed before, are groups of coils configured so that the magnetic lines of flux from one coil, are shared with another nearby coil. This causes the electric power from one coil to be transferred magnetically to the second coil. If the second coil has more turns or "loops" than the first coil, the voltage is stepped down. If the second coil has fewer turns than the first coil, the voltage is stepped up to a higher voltage. The ratio that the voltage is stepped up or down is the same as the ratio of the number of turns in the first coil to the number of turns in the second coil. Example: In this example, assume we have a transformer with 5 turns on the input, and 15 turns on the output. That's a 5:15 ratio - same as a 1:3 ratio.

Lesson 50 - Class C Amplifiers
You will recall that most AF amplifiers use cathode bias. The audio amplifier tubes are operated ad Class A or Class B, because we are interested in obtaining good fidelity. The Class A amplifier sacrifices efficiency for fidelity. In the case of an RF amplifier, we are not interested in fidelity, since we are not amplifying an audio signal. We ARE interested in EFFICIENCY of operation. We do not want to use more energy than necessary in order to accomplish effective communications. An RF amplifier operates most efficiently in a transmitter as a Class C amplifier. In order to operate the tube as a Class C

amplifier, the bias must be between one and on-half to four times the bias value necessary for cut-off. This condition is shown graphically in the diagram to the left. You will notice that with a pure sine wave applied to the grid, the plate current consists of small pulses which certainly do not resemble the input sine wave. Since the plate current wave does not resemble the grid signal, the fidelity of a Class C amplifier is poor. One important point to notice is that the plate current flows only for a fraction of a complete cycle of the input signal. Compare this to a Class A amplifier, where the plate current flows continuously. Obviously more power is wasted in plate dissipation in a Class A amplifier as compared to a Class C amplifier. Since the plate dissipation is decreased in the Class C amplifier, the useful power output is increased. The efficiency of a Class C amplifier is therefore excellent. It is approximately 70% efficient. The exact efficiency depends upon the bias voltage, the load impedance, the incoming signal amplitude, the plate voltage, etc...

Note in the above illustration, that the input signal drive is quite large. This is so because the input signal must overcome the high negative bias and drive the grid positive. The question that always arises at this point is: Of what good are the plate current pulses if we are interested in obtaining an amplified version of the sine wave input? The answer lies in the ability of the plate tank circuit to reproduce a pure sine wave from pulses of energy which are applied to it every cycle. From the discussion of the oscillatory circuit, it will be recalled that when the plate tank circuit is tuned to the resonant frequency of the grid circuit, the plate current pulses will reinforct the oscillations in the plate tuned circuit at just the right instant, and therby sustain the oscillations. The surges of plate current five the tank circuit the shot of energy which resusts in the tuned circuit making up that portion of the sine wave missing in the plate current pulses. This is known as the FLYWHEEL EFFECT. Thus, we see that although the plate current is made up of pulses, the signal fed to the antenna or the next stage is a pure sine wave!

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