Chapter 3 Introduction to Basic Electrical Circuit Materials 71
resistance value. The second band represents the second
digit of the resistance value. The third band is called the
multiplier. The multiplier gives the factor of ten that the first
two digits should be multiplied by. The fourth band repre-
sents the tolerance of the resistor. Resistor tolerance is a
reflection of the precision of resistor’s value. If a 20 ohm
resistor has a 10% tolerance, the resistor’s value can vary by
± 2 ohms. In this case the resistor can have a true resistance
value of 18 to 22 ohms. A fifth band is sometimes used to
indicate resistor reliability or expected failure rate.
See Figure 3-38. In the first sketch, the first bar is
red and the second bar is violet. Checking the color code
chart shows the first two digits in the resistor’s value to be
2 and 7 (or 27). This number is then multiplied by the
third band. The third band is brown ( 10). This indicates
that the value 27 is multiplied by 10, for a final value of
270 ohms. This is what the resistor value would be if the
resistor was perfect. However, the fourth band is silver.
This indicates that this resistor has a tolerance of 10
percent. In this example, the tolerance is a ±27 ohms
(270 0.1 = 27). Thus the value of this resistor is some-
where between 243 ohms and 297 ohms.
Work out the stated value, maximum value, and min-
imum value for the other two sketches in Figure 3-34 on
your own.
Review Questions for Section 3.5
1. Write the color codes for the following resistor val-
ues (first color, second color, multiplier, tolerance).
a. 2400 Ω, 10%
b. 680 Ω, 5%
c. 91,000 Ω, 20%
d. 27 Ω, 10%
e. 3600 Ω, 5%
f. 100 Ω, 10%
g. 5.1 Ω, 5%
h. 9.1 MΩ, 10%
red
2
violet
7
brown
10
silver
10 percent tolerance
orange
3
white
9
black
1
no fourth color band
20 percent tolerance
green
5
blue
6
orange
1000
gold
5 percent tolerance
1
3 2
Figure 3-38. Examples of standard color-coded resistors.
First Band
1st Digit
Second Band
2nd Digit
Third Band
Multiplier
Fourth Band*
Resistance Tolerance
Color Digit Color Digit Color Multiplier Color Tolerance
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Black
Brown
Red
Orange
Yellow
Green
Blue
Silver
Gold
Silver
Gold
*No Band
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
1
10
100
1,000
10,000
100,000
1,000,000
0.01
0.1
10%
5%
20%
Figure 3-37. Standard color code for resistors.