Resistance Color Code

Electrical resistances are mass-produced by mixing graphite (a conductor) with clay (an insulator), molding the compound with a binder (glue) with metal wires imbedded for electrical contacts.  They cost pennies apiece.  The resistance is governed by the ratio of clay to graphite.  Possible values of electrical resistance in these devices ranges from 10 Ohms to about 20 Million Ohms (2 x 107) Ohms. The physical size of the resistor determines how much power the resistor can absorb without overheating.  The most common physical size available in the lab will dissipate ¼ Watt.

Printing the resistances on the resistors would cost more than making the resistors themselves.  The industry has adopted a color scheme for labeling resistors.

The colorcode consists of three colors, each color corresponds to a decimal digit, and a tolerance (gold, silver).  The digits are coded according to the following table:



0 Black
1 Brown
2 Red
3 Orange
4 Yellow
5 Green
6 Blue
7 Violet
8 Gray
9 White

Think of your own mnemonic for this code.  Notice the colors of the rainbow.

To read a resistorís value, begin on the end of the resistor opposite the tolerance.  The colors then read 1st digit, 2nd digit, decimal power, tolerance.

For example, red, green, orange, gold is 2 5 x 10orange = 25 x 103 = 25,000 Ohm = 25 KW. ± 5%.  (Gold represents 5%, silver represents 10%)

The colors to represent a 150 Ohm resistor, 10% tolerance, are brown, green, brown (15 x 101) silver.

Remember, there is no decimal point, and the third color is a power of 10 (a logarithm)


Give the colors for the following:
a)  100 Ohm   b)1 M Ohm
b)  c) 10 k Ohm d) 500 Ohm

Give the resistance values for the following:

a)  Brown, Black, Yellow
b)  Red, Red, Red
c)  Orange, Orange, brown
d)  Brown, Green, Black