J&J Science Kit #1: Basic Electricity and Electronics

Basic Electricity

All matter is made of atoms. All atoms are made of electrons, protons, and neutrons. The protons and neutrons sit together in the middle of the atom in a clump we call the nucleus. The electrons are kind of like little planets that orbit around the nucleus. If you grab an electron and pull it away from its nucleus, it won’t like it. This is because electrons have a negative charge. The protons in the nucleus have a positive charge. When one thing has a negative charge and another thing has a positive charge, they pull towards each other. So, when we let go of the electron, it is pulled back to its atom.

Batteries are devices that pull the electrons off some atoms, and put them on one terminal of the battery. We call this the negative terminal. To get back to their atoms, the electrons need to get to the other terminal, which we call the positive terminal of the battery. Once back, the electrons are pulled off again for another trip. We can build a little road made of wires for the electrons so they can go from the negative terminal to the positive terminal, and back to their atoms.

By putting various components in the road, we can get the electrons to do useful things for us on their way to the positive terminal. We build most of our roads out of metal wires. Electrons can move through metal wires very easily. Part of our road might include a light bulb. When the electrons go through the wire in the light bulb it gets hot, causing it to glow. So, electricity is a phenomenon involving lost electrons that are trying to get back to their atoms. We care about electricity because we can build little roads, or circuits, to make the electrons do things for us.

e e Negative Positive Terminal Terminal (-) (+) 9 Volt Battery

1 Section 1: Current, Resistance, and Voltage

Current, resistance and voltage are the three basic units used when dealing with electric circuits.

Current

Imagine a wire with electrons running through it. Of course, electrons are much too small to see, but imagine that you are really small and you can see the electrons moving along through a little window.

e e e e e e

Let’s say you count how many electrons go by the window each second. You are measuring current. If you count ten electrons going by each second, the current is twice as high as five electrons per second. Current is a measure of the number of electrons that flow through a section of wire each second. Of course, since electrons are really tiny, we need a lot of them go by each second to be useful to us. A current of ten electrons per second is too small to measure. We need to talk about lots of electrons.

You’ve heard words like dozen (12) and gross (144). We count eggs in dozens. We count electrons in coulombs. Where one dozen is 12, one coulomb is about 6,000,000,000,000,000,000 (6.24151 × 1018). Now, if we measure current in coulombs per second we can talk about lots of electrons per second. But who wants to write “coulombs per second” again and again? No one does. So, someone decided that we would call a coulomb per second one Ampere. If we measure the current in a wire, and our meter says 3 Amperes, that means there are 3 coulombs flowing through the wire per second. Remember, current is not a number of electrons, but a number of electrons moving per second.

2 Resistance

Resistance holds the electrons back. All materials have resistance. Materials with a very low resistance are called conductors. These include copper, iron, aluminium, gold, and other metals (as well as some things that are not metal). Materials that have a very high resistance are called insulators. Examples are plastic, rubber, glass, and air. Electrons do not flow though insulators easily.

Since the air is an insulator, with a very high resistance, the electrons can not use it to get from one battery terminal to the other. If you connect two battery terminals together with wire, current will flow. The problem is that too much current will flow. So, don't do that. All that current will make the wire and battery get hot, and the battery will quickly be drained of energy. You could even start a fire, or cause the battery to leak. Luckily, we have a component called a resistor. A resistor looks like a little can or tube with a wire sticking out of each end. They are usually painted with colored stripes.

Every resistor has a resistance value. The resistance of a resistor is measured in ohms (). So, a resistor with a low resistance, say 1 , will let a lot of current through. Resistors with a higher resistance, like 1,000  (1 k), will not let as much current through. Resistors resist the flow of current.

Voltage

All things have resistance, even metal. So why does current flow? The answer is because of voltage. Sometimes, it’s useful to think of electricity as being like water. The current is the amount of water going through a hose. A thinner hose has a higher resistance than a thicker one. The voltage is the water pressure. As you turn up the knob, the water pressure goes up. Voltage is measured in volts (V). A 9 V battery (nine-volt) has more electrical pressure and will cause more current to flow than a 6 V battery.

An important thing to understand about voltage is that it is not the same type of quantity as current. We measure the current that passes through a point in our circuit. A voltage measurement is always a comparison of two points. So, one point in a circuit can not be 3 volts. It could be 3 volts higher than some other point. A nine-volt battery is called a nine-volt battery because the positive terminal is 9 volts higher than its negative terminal.

3 Quantities, Units, and Symbols

The three main quantities used in electronics are voltage, current, and resistance. We measure the voltage across a component. We measure the current through the component. We measure the resistance of a component. Each quantity has an associated symbol. This symbol is used as a variable when the quantity is used in an equation. Each quantity also has a unit to be used with actual values.

Current is the measurement of the rate at which electrons move through something. The symbol for current is I. The unit for measuring current is amperes, which is abbreviated, A.

Resistance is a measurement of how an object holds back the current when a voltage is applying electrical pressure to the object. The symbol for resistance is R. Resistance is measured in ohms, which is abbreviated, .

The symbol for voltage is V. Voltage is measured in volts, which is abbreviated, V. Voltage is the electrical pressure caused by the separation of electrons from atoms. Resistance resists this pressure. The current depends on both. If the voltage is increased, or the resistance is decreased, more current will flow. A voltage is a relative measurement. This means you can only measure the voltage difference between two points.

Quantity Symbol Unit Abbreviation Current I Amperes A Resistance R Ohms  Voltage V Volts V

4 The Digital Multimeter

A meter is a device that measures something. A multimeter measures a bunch of things (like voltage, resistance, and current). A digital meter has a digital display, like a digital clock or a calculator rather than a needle like a car speedometer.

The DMM (Digital multimeter has settings for voltage current and resistance. Be sure the meter is on the proper setting before connecting it to a circuit. The meter also has range settings. Each range setting is labeled with the maximum value that can be measured at that setting. The meter should always be set to the first range setting above the value to be measured. For example, when measuring a 0 to 5 volt signal, the meter should be set to the 20 volt setting, because this is the first range above 5. Setting the meter to the wrong range will not damage the meter, but you will not get a reading.

Never apply a voltage (try to measure a battery, or a powered circuit) when the meter is set to measure current or resistance. You might break the meter.

The jacks are for plugging probes into. A black probe should be plugged into the common or ground jack. A red probe should be connected to the V//A jack. Note that on some meters, a separate jack may be used for current measurement. The jacks will be labeled.

Section 2: Ohm’s Law

In the last section, we learned about voltage, current, and resistance. We also learned that these three quantities are related. When a voltage source (a battery) is put across a resistance (a resistor or circuit) current will flow. If we increase the voltage of the source, more current will flow. If we increase the resistance, less current will flow. This gives us some understanding about how electric circuits work, but it is a bit vague. If we double the voltage, will that cause the current to double, or will it be four times as high? We need to be more specific about this relationship if we want to solve real problems. For instance, if we have a 9 V battery connected across a 100  resistor, how much current, in Amperes will flow? This is where math comes in.

In the early 1800’s, a German physicist named Georg Simon Ohm showed how voltage, current and resistance are related mathematically. We call this equation Ohm’s law.

V = IR (Ohm’s law)

For any resistor, the voltage across that resistor is equal to the current flowing through that resistor, times the resistance of the resistor. So, if I have a 5  resistor, and 2 A flow through it, there must be 10 V across it.

The equation may seem more intuitive if we write it in a different form. If we divide both sides of Ohm’s law by R, we get the equivalent equation, V I R

Now, looking at the equation in terms of current, we can see that if we double V, that side of the equation (V/R) will be doubled. Since the current is equal to V/R, the current will also double. We say that the current is directly proportional to the voltage. Also, notice that if R increases, the fraction V/R decreases because R is in the denominator. So, when the resistance goes up, the current goes down by the same amount. We say that the current is inversely proportional to the resistance. So, Ohm’s law agrees with what we know. It says that an increase in voltage causes an increase in current, and an increase in resistance caused a decrease in current. It also shows us that there quantities have a simple linear relationship.

Now, we can answer our question. If we have a 9 V battery connected across a 100  resistor, how much current will flow? According to Ohm’s law,

V 9 V I 90mA R 100

90 mA of current will flow.

6 So, using Ohm’s law, we can find the current in a resistor if we know the voltage across the resistor and the resistance. In fact, if we know any two of these quantities, we can find the third. Below are the three forms of Ohm’s law. The first is used to find voltage, and the second is used to find current. We’ve seen these already. If we divide both sides of the first form by I, we get the third form, which we can use to find the resistance if we know the voltage and current.

V V V IR I R R I

Examples:

a. If we apply 4 V across a 500  resistor, how much current will flow?

We divide both sides of the basic form of Ohm’s law (V = IR) by R. V 4V I 8mA R 500

b. If we apply 12 V across a resistor, and measure the current to be 100 mA, what is the resistance of the resistor?

This time we divide both sides of Ohm’s law by I. V 12V R 120 I 100mA

7 Section 3: Electrical Circuits

Schematic Diagrams

When we work with a circuit, we often want to draw a picture of it. It would look silly to draw little pictures of batteries and resistors, so we use symbols. A picture of an electrical circuit that uses these symbols is called a schematic diagram (or schematic for short). The schematic below shows a 6 V battery (or a 6 V power supply) connected to a 100  resistor.

6 V 100 

As you can see in the schematic above, a battery is represented by the symbol below, Positive terminal

Negative terminal which is formed using alternating long and short lines. The side with a long line (and a + sign) is the positive terminal. The side with the short line (and the – sign) is the negative terminal. A battery is a polarized component. That means if you put it in backwards, it will make a difference. You need to pay attention to the polarity of a battery or voltage source when you connect it to a circuit.

Resistors are represented by the zigzag symbol shown below.

A resistor is not polarized. It doesn't matter which way you connect it. You can’t put it in backwards.

Wires are represented by straight lines. Although all wires have some resistance, it is usually so small that we ignore it. The lines in a schematic are ideal wires that have no resistance (0 ).

8 Conventional Current Flow

Years ago, when Ben Franklin was experimenting with electricity, he guessed that small particles were moving through the wires, making them hot. He had no way to know in which direction these particles were moving. He guessed that they were moving from the positive terminal to the negative terminal. We now know that electrons move from the negative terminal to the positive terminal. Still, we keep the convention that has been used for many years. We treat current as if it flows from the positive terminal of a voltage source to the negative terminal. This is called conventional current flow. It is backwards compared to reality, but it works just as well.

The following circuit shows an example of conventional current flow. A 40 V battery is connected across a 20  resistor. We say that 2 A of current flow in the direction of the arrow.

40 V 20 

Ground

If I ask you how high up you are, and you answered “five miles above”, I still wouldn’t have a useful answer. You could be five miles above the ocean, or the land, or the center of the Earth. Distance is only a useful measurement if I know where zero is. Voltage works the same way. One point in a circuit can be 5 volts higher than another, but it doesn’t make sense to say that a point in a circuit is 5 volts. Likewise, one terminal of a battery can not be 9 volts. It can be 9 volts higher than the other terminal, as with a 9 V battery. Looking at a 9 V battery, we could say the two terminals are:

0 V and 9 V, -9 V and 0 V, or 10 V and 19 V.

The terminals do not have a voltage. There is a difference in voltage between them. For convenience, we can choose zero volts to be wherever we like. If we choose the negative terminal of a 9 V battery to be zero volts, then the positive terminal is 9 volts. A point in a circuit that is zero volts is called ground.

9 We use a ground symbol in a schematic to show which part of the circuit is zero volts. Since the ideal wires have no resistance, the three schematics below all show that we are choosing the negative terminal to be at zero volts.

9 V 9 V 9 V

To measure points in a circuit compared to ground. Just put the black meter probe on ground. Put the red probe on the point you wish to measure. If you measure the voltage on the top of the resistor in the circuit above, the meter will say 9 V. This means 9 volts above ground.

Breadboards

Normally, electric components in a circuit are soldered together. When engineers want to prototype a new circuit (build and test it), they use a breadboard. An illustration of a simple breadboard is shown below.

A breadboard is covered with little holes that you can stick wires into.

10 If you could see through the plastic top of the breadboard, you would see that strips of metal connect some of these holes. There are short strips and long strips. Breadboards usually have one or two long strips on each side and a bunch of short strips in the middle.

These 5 holes are all connected to each other but not to any other holes.

These 15 holes are all connected to each other but not to any other holes.

We can plug components into these holes to connect them together. Don't do this

If we plug a resistor into the breadboard as shown above, we have made this circuit.

11 This is not a particularly useful circuit. We have connected the resistor to itself, and that won't do anything. If we plug the two terminals of a battery into the same holes, we have the circuit shown below.

Don't do this

Here, we have connected the battery terminals together. Not only is the circuit not useful, the wires and battery will get hot. Current will flow as fast as the battery can supply it, and the battery will quickly be drained.

A more useful circuit is shown below.

The breadboard connects the positive terminal of the battery to one end of the resistor, and the negative terminal to the other end of the resistor.

12 Measuring Current

To measure voltage, we use the V setting on the meter. When the meter is in voltage mode, it has a very high resistance. This is good. It means that very little current flows through the meter. That way, the circuit isn't affected much by measuring a voltage. However, current isn't something that we measure across a component. Current goes through the resistor. To measure the current, it has to go through the meter as well. So, we need to break the circuit, and use the meter as a bridge. In current mode, the meter has a very small resistance so that it will not affect the circuit. In the circuit below, the current leaves from the battery, and goes through the breadboard to the resistor (A). After going through the resistor, the current goes through the breadboard to the meter (B). After going through the meter, the current goes through the breadboard to the negative terminal of the battery (C).

C Meter Meter

Common Mistake: Since a meter in current mode has a very low resistance, if it is connected across a battery lots of current will flow. This may blow a fuse, or damage the meter. Sometimes people forget and leave the meter in current mode when measuring voltage. Make sure you always turn off your meter (or change it to voltage mode) after making a current measurement.

13 Section 4: Resistors in Series

What happens if we connect several resistors together? Well, there are many ways to connect resistors together. In this chapter, we will look at resistors connected in series.

The three resistors above are connected in series. Aside from the endpoints, each resistor is connected to exactly one other resistor. A more common (and more picky) way to define a series connection is this. When resistors are in series, the same current (I) flows through all of them. That makes sense. If you know how much current flows through the first resistor, the current must be the same in the second resistor. It can't be lower in the second resistor, because the current has to go somewhere when it leaves the first resistor, and there is nowhere else for it to go. It can't be higher in the second resistor, because current has to come from somewhere, and there isn't any other place for it to come from aside from the first resistor. The connections between the resistors are marked above with a node (a little black circle). The current entering a node must be equal to the current leaving a node. This is called Kirchoff's current law.

Variable Subscripts

Before moving on, we should talk about subscripts. A subscript is a little number, letter, or word that we write next to a variable. In the series example above, we were lucky. The current, I, for all three resistors is the same, so we didn't have to worry about telling the I's apart. But, what if we wanted to talk about currents that are not the same? We can call them I1, I2 and I3. The 1, 2 and 3 are subscripts.

Let's look at that series resistor example again, and label it properly. We don't know the values of the resistors, so we need a different variable for each. We can use R1, R2 and R3. Now, when we talk about the current in each resistor, we need three current variables. Just so it's easier to remember what the variables mean, we will use IR1, IR2 and IR3. R1 is the first resistor, and IR1 is the current through R1.

R R R 1 2 3

I I I R1 R2 R3

Since the resistors are in series, we can say: IR1 = IR2 = IR3.

14 Total Resistance

So, now that we know what resistors in series are, we can get back to our question. What happens when you connect resistors together? If you connect three resistors in series, as shown below, what will the total resistance be between points A and B?

R = 1 k R = 1 k R = 1 k 1 2 3 A B

You could build this simple circuit, and measure the resistance with a meter. Or, you might guess that you can add the values to get 3 k. If you did guess that, you were right. If the electrons find it hard to go through one resistor, it will be harder to go through two or three. To find the total resistance of a series circuit, add the values of the individual resistors. In the form of an equation, we could say that the total resistance, RT, is the sum of the individual resistances.

RT = R1 + R2 + R3 + R4 + …

You can think of this as a new equation to memorize, or just as common sense.

Example:

What is the total resistance of the series shown below?

R = 700  R = 2.1 k R = 500  R = 5 k 1 2 3 4

RT = R1 + R2 + R3 + R4

RT = 700  + 2.1 k + 500  + 5 k

RT = 8.3 k

15 Voltage in Series Circuits

What is the voltage across each resistor in a series? We know that the current is the same in each resistor, but there is no reason to believe that the voltage will be the same. In fact, if the resistors have different values, the voltage across them will not be the same.

I = R = 5 k 857 A 1

R = 7 k 12 V 2

R = 2 k 3

The total resistance is the sum of the individual resistors, 14 k. Then the current is:

I = V/R = 12 / 14,000 = 857 A

Now we know the resistance of each resistor, and the current in each resistor. According to Ohm's law, V = IR.

VR1 = IR1 = 857 A  5 k = 4.3 V

VR2 = IR2 = 857 A  7 k = 6 V

VR3 = IR3 = 857 A  2 k = 1.7 V

Note that if we add these 3 voltages together, we get 12 V, which is the battery voltage. The sum of the voltages in a series circuit must always equal the voltage of the battery. That is called Kirchoff's voltage law.

Also, notice that the highest value resistor (R2 = 7 k) has the highest voltage across it. This makes sense. Ohm's law says V = IR, and the current is the same in every resistor. So, if the resistance is higher, the voltage must be higher too. Another way to look at it is this. If a resistor is harder for the electrons to travel through, you need to apply more voltage. We often refer to the voltage across a component as a "voltage drop". When resistors are in series, a higher value resistor will cause a higher voltage drop.

16 Section 5: Resistors in Parallel

A parallel circuit is kind of the opposite of a series circuit. Instead of the current going through every resistor, it splits up and some goes one way, some goes another.

Components are considered to be in parallel if they are connected to each other at both ends.

Total Resistance

Since the current splits up, it has more places to flow through. This means it is easier for the electrons to get through.

The equation for the total resistance is not as obvious as it was for resistors in series. Instead of adding the resistor values, we add the reciprocals. This number is the reciprocal of the total resistance.

1 1 1 1 1

RT R1 R2 R 3 R4

17 So, we take the reciprocals of all the resistor values. Then we add them up. Finally, we take the reciprocal of the sum. Another way to write the equation is shown below. Both equations are equivalent. If you take the reciprocal of both sides in the equation above, you get the equation below.

1 R T 1 1 1 1

R 1 R 2 R 3 R 4

So, let's say we have three 300  resistors in parallel.

300  300  300 

The reciprocal of 300 is 0.00333… We add the three reciprocals up and get 0.01. The reciprocal of 0.01 is 100.

So the total resistance is 100 . Notice that it is smaller than 300.

Section 6: Switches

A switch is a very simple component. The schematic symbol for a switch is shown below.

There are many types of switches, and some are pretty complicated. We are only going to talk about the simplest switch there is. It is called a single pole single throw (SPST) switch. This switch has two positions. In the open position, the switch acts as an open circuit. It does not allow any current to flow. It acts very much like a broken wire. In the closed position, the switch acts like a short circuit. The switch acts like a wire, and allows current to flow.

A Simple Switch Circuit

Let's use a switch to turn an LED (Light Emitting Diode) on and off. All we need to do is put a switch, a resistor, and an LED in series. When the button is pushed, the switch closes and current flows through the LED.

1 k

Logic Gates

A logic gate creates an output using information from inputs. In this case, the output is the LED, and the inputs are buttons. We will discuss three gates; the AND gate, the OR gate, and the inverter (or NOT gate).

The output of an AND gate is only high when all of the inputs are high. (The light only comes on when all of the buttons are pushed.) We can see why by looking at the circuit. Since the switches are in series, current can only flow if all of the switches are closed.

19 The circuit below only has two inputs, but an AND gate may have any number of inputs. We will call the buttons A and B. The LED will light if A AND B are pushed. That's why it's called an AND gate.

A B 1 k

The output of an OR gate is high if any input is high. Again, we can see why by looking at the circuit. Since the switches are in parallel, current can flow if any one (or more) of the buttons is pushed. The LED will light if you push A OR B. That is why it's called an OR gate. This OR gate only has two inputs, but an OR gate can have any number of inputs. A

1 k B

The inverter is weird because it only has one input. If the input is high, the output is low. If the input is low, the output is high. An inverter makes the output the opposite of the input. Sometimes it is called a NOT gate, because the output is not what the input is. The LED stays lit unless you press the button. Pushing the button gives the current a short circuit path back to the battery, so it does not flow through the LED.

1 k

20 Section 7: Engineering Notation

If we measure the current flowing through a wire, and it is 5 amperes, we can abbreviate amperes by using a capital A. We write, 5 A (note the space between the number and the unit). So far, this works pretty well. What if the current is 5,000,000 A, or 0.000005 A? That’s a lot of zeros to write. And who wants to say, “zero point zero zero zero zero zero five amperes”? We need a better way to talk about big and small numbers. We don’t measure the distance between cities in inches. We use miles. But we don’t want to have a whole bunch of different units for current, and have to convert between them all the time.

We could use scientific notation. In scientific notation, we express all values as a number between one and ten (including one but not including ten), multiplied by a power of ten. Since multiplying by a power of ten just shifts the decimal point, the power of ten makes up for rewriting the first part as a number between one and ten. For example, 5,000,000 can be written as 5 x 106. And 0.000005 is written as 5 x 10-6.

The table below shows some examples of scientific notation. Look at the left half of the scientific notation value. Notice that the number gets bigger as the value increases, until it reaches ten. Then the power of ten increases, and the number starts back at 1.

Decimal Number in Number Scientific Notation 1 1 x 100 2 2 x 100 5 5 x 100 9 9 x 100 10 1 x 101 11 1.1 x 101 17 1.7 x 101 25 2.5 x 101 89 8.9 x 101 99 9.9 x 101 100 1 x 102 130 1.3 x 102 190 1.9 x 102 200 2 x 102 500 5 x 102 990 9.9 x 102 1,000 1 x 103 8,000 8 x 103 50,000 5 x 104

21 Engineers tend to use what is called “engineering notation”. It’s almost the same thing as scientific notation. The rules are just a little different. The first part is a number between 1 and 1,000 (including 1, but not including 1,000). The rest works like scientific notation, except the exponent must be a multiple of 3 (3, 6, 9, -3, -6, -9…). Using engineering notation, we would write 0.000034 A as 34 x 10-6. This might not seem very useful at first, but here’s where the metric system comes in. The metric system defines a prefix for each power of ten (aside from zero). 101 = deka, 102 = hecto, 103 = kilo, and so on. On top of that, each prefix has an abbreviation. Deka = da, hecto = h, and kilo = k.

The prefix for 10-6 is micro (abbreviated with the Greek character mu, ). So, our current of 0.000034 A can be called 34 microamps, and written as 34 A. (Note that there is a space between the number and the prefix, but not between the prefix and the unit.)

The really handy part about using engineering notation is, since the powers of ten are multiples of three, you don’t need to remember a bazillion prefixes. In fact, for now these six are all you’ll need.

106 = mega M 103 = kilo k 10-3 = milli m 10-6 = micro  10-9 = nano n 10-12 = pico p

Let's look at some examples.

5 A = 5 A (5 amps is 5 amps…) 5,000 A = 5 kA (5 thousand amps is 5 kilamps) 5,000,000 A = 5 MA (5 million amps 5 is megamps) 0.005 A = 5 mA (5 one-thousandths of an amp is 5 milliamps) 0.000005 A = 5 A (5 one-millionths of an amp is 5 microamps)

22 Decimal Number in Engineering Number Scientific Notation Notation 1 A 1 x 100 A 1 A 5 A 5 x 100 A 5 A 9 A 9 x 100 A 9 A 10 A 1 x 101 A 10 A 17 A 1.7 x 101 A 17 A 25 A 2.5 x 101 A 25 A 99 A 9.9 x 101 A 99 A 100 A 1 x 102 A 100 A 130 A 1.3 x 102 A 130 A 500 A 5 x 102 A 500 A 990 A 9.9 x 102 A 990 A 1,000 A 1 x 103 A 1 kA 8,000 A 1 x 103 A 8 kA 50,000 A 5 x 104 A 50 kA 95,000 A 9.5 x 104 A 95 kA 130,000 A 1.3 x 105 A 130 kA 500,000 A 5 x 105 A 500 kA 900,000 A 9 x 105 A 900 kA 1,000,000 A 1 x 106 A 1 MA 7,000,000 A 7 x 106 A 7 MA 18,000,000 A 1.8 x 107 A 18 MA

Look at the first and last columns. At the top of the table, they are the same. At the bottom, things get interesting. When the numbers get big (one thousand or more), we use a “k” to show that we’re in the thousands, and start back at 1. An “M” shows we are in the millions.

It’s just like using miles to measure long distances instead of inches, except since the prefixes mean multiplication by 10 (really a multiple of 10, like 1,000 or 1,000,000), the relationship is much more obvious.

23 Resistor Color Codes

You can tell the resistance value of a resistor just by looking at it. The colored stripes are a code.

Each color is a number. Memorize this table. Black = 0 Brown = 1 Red = 2 Orange = 3 Yellow = 4 Green = 5 Blue = 6 Violet = 7 Gray = 8 White = 9

Start reading at the stripe that is closest to an edge, and isn't gold. The first stripe is the first digit of the resistance value. The second stripe is the second digit of the resistance value. The third stripe tells you how many zeros to put after the second digit. In other words, resistance is rated using two significant digits multiplied by some power of 10.

For example,

Green Red Orange

5 2 000

52,000  or 52 k