Resistors

In this presentation you will: discover how to use multimeters to measure

resistance identify how resistors can be used in

circuitsNext >

Resistors are commonly used in electronic circuits to control voltage and current.There are several different types of resistors that can be used.

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Introduction

The type of resistor used has to be appropriate for the application. A low power resistor.

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Resistors

A high power resistor.

Several resistors in one package (resistor arrays).A rheostat (variable resistor) for experimentation.

The value of a resistor, its resistance, is measured in ohms (). This indicates how much it reduces the current flow.

A higher value of resistance reduces the current flow more than a lower value resistance. Next >

Resistors

It is common to use , k and M values for resistors.

There are 1,000 in a k (kilohm).There are 1,000 k in a M (megohm).So, there are a million ohms in a M.

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These multiples should be used to ensure that there will never be more than three digits in a resistor value.

1 M = 1,000,000

1 k = 1,000

For example, a 4,700 resistor is usually expressed as 4.7 k.

Powers of 10

Question 1

How many ohms does a 3.9 k resistor have?

A) 39

B) 390

C) 3,900

D) 39,000

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Question 1

How many ohms does a 3.9 kW resistor have?

A) 39

B) 390

C) 3,900

D) 39,000

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Some resistors are too small for their values to be printed on them.

The value is displayed by a series of colored bands.

The simplest color code is one that has four bands.

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In order to read the code, it is necessary to get the resistor the right way round.

Arrange the resistor so that the band on its own is on the right.

Resistor Color Code

The table gives a list of the colors and their associated values.

Write down the value for band A.Write down the value for band B.

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Band C gives the number of zeros to add to the two numbers you have already written down.If band C is black, add no zeros.

The number you have written down is in ohms. Convert it to kilohms or megohms if necessary.

Band A

Band B

Band C

Band D

Resistor Color Code

Band A

Band B

Band CBand

D

Here is an example:

Band A is yellow: the value is 4.

Band B is violet: the value is 7.

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Band C is red: add two zeros.

This gives 4,700 .

This is equivalent to 4.7 k or 4K7.

Yellow Violet Red Gold

4 7 00

Resistor Color Code

What about the fourth band, band D?This gives the tolerance of the resistor. It is often called the tolerance band.

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This indicates the accuracy of the value given by the first three bands.

In the example, the fourth band is gold. This means the value is within 5% of 4K7.

5% of 4K7 is 235 . So, the value is 4,700 ± 235 (between 4,465 and 4,935 ).

A B C D

ToleranceColor

Resistor Color Code

Question 2

What is the color code for a 3.9 k resistor?

A) orange, white, blue

B) orange, white, black

C) orange, white, yellow

D) orange, white, red

Significant Figures

Number of ZerosColor

Gray

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Question 2

Significant Figures

Number of ZerosColor

Gray

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What is the color code for a 3.9 k resistor?

A) orange, white, blue

B) orange, white, black

C) orange, white, yellow

D) orange, white, red

A resistor also has a power rating.This is a measure of the energy it can dissipate safely. It is calculated by multiplying

the voltage across the resistor by the current flowing through it.

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The unit of power is the watt (W). Resistors are usually available in 0.25 W, 0.5 W, and 1 W.Most electronic circuits in schools and colleges use low power resistors of 0.25 W.

P = VI

0.25 W

0.5 W

1 W

Power

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Full brightness occurs when the lamp is connected directly to the power source.

The lamp is dimmed when the switch connects the lamp to the power source through the resistor.

Light Dimmer Circuit

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This circuit has an option to control lamp brightness. In an ideal circuit, the connecting wires should have no resistance.

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Resistance is usually measured by a multimeter set to the ohmmeter range.

The component must be removed from the circuit and connected to a multimeter.

Measuring Resistance

In order to make the math easier, we often use resistors with simple values in science.

These resistors are often made by winding the correct length of wire around a former.

Resistors in Simple Science Experiments

It is much easier to do calculations with values, such as 1 Ω, 2 Ω, 5 Ω, and 10 Ω rather than 2.2 Ω or 6.8 Ω.

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Question 3

Connecting wires in circuits are usually made of copper. Why is this?

A) Copper is an inexpensive metal

B) Copper does not break

C) Copper has a low resistance

D) Copper does not react with other chemicals

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Question 3

A) Copper is an inexpensive metal

B) Copper does not break

C) Copper has a low resistance

D) Copper does not react with other chemicals

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Connecting wires in circuits are usually made of copper. Why is this?

Question 4

If the resistor in this circuit was changed from 10 to 20 what would happen to the lamp?

A) It would get brighter

B) It would dim

C) There would be no change in the lamp

10

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Question 4

If the resistor in this circuit was changed from 10 to 20 what would happen to the lamp?

10

A) It would get brighter

B) It would dim

C) There would be no change in the lamp

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In this presentation you have seen:

different types of resistors

how resistors can be used in circuits

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how to use a multimeter to measure resistance

Summary