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## 6.6 ELECTRICAL COMPONENTS

### 6.6.1 Resistors

Resistors are circuit elements that limit the flow of current in a circuit. The basic equation W = I 2 R relates the amount of heat dissipated by a resistor to the current flowing through the resistor. Thus, a resistor that passes 1.5 A of current and whose rating is 500 ? dissipates (1.5) 2 500 = 1125 W power.

There are various common forms of resistors in use:

• Carbon composition

• Metal film

• Wirewound (precision and power types)

• Filament or ribbon (power types)

• Cast-alloy element (power type)

Refer to Fig. 6.3 and the accompanying listing for an explanation of the color code for carbon composition resistors.

Figure 6.3: Carbon composition resistors and color code.

Color

1st digit (A)

2d digit (B)

Multiplier (C)

Tolerance (D)

Black

0

0

1

Brown

1

1

10

Red

2

2

100

Orange

3

3

1000

Yellow

4

4

10000

Green

5

5

100000

Blue

6

6

1000000

Violet

7

7

10000000

Gray

8

8

100000000

White

9

9

Gold

0.1

5%

Silver

0.01

10%

No color

20%

Precision wirewound and carbon-film resistors have the resistance value and tolerance (usually 1 percent) marked on them.

Maximum Continuous Working Voltage across a Resistor

where P = power, W ( I 2 R); R = resistance, ?.

Example. How many...

##### Products & Services
Resistors
Resistors are electrical components that oppose the flow of either direct or alternating current. They are used to protect, operate, or control circuits.
Resistors and Potentiometers
Resistors and potentiometers are passive electronic components that oppose the flow of either alternating current (AC) or direct current (DC).
Chip Resistors
Chip resistors are passive resistors with a form factor of an integrated circuit (IC) chip. Typically, they are manufactured using thin-film technology.
Current Sensing Resistors
Current sensing resistors convert the current flowing through it to a voltage drop. Monitoring or measuring this voltage drop allows the current through the resistor to be measured. Applications for current sensing resistors include power supplies, receptacles, and battery packs.
Shunt Resistors
Shunts resistors are connected in parallel with an instrument or component to divert electrical current. They provide an alternate path for current in case of failure.

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