Question

What is colour coding of resistor? Explain with examples to find the resistance.

Answer 1

A colour code is used to indicate the resistance value and its percentage reliability.

The resistor has a set of concentric rings A, B, C, D Fig. on it with their significant value as in Table

To read the value of carbon resistance, the following sentence is found to be of great help:

B B ROY Great Britain Very Good Wife

The bold face letters in the above sentence correspond to the colour Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Grey and White respectively. The colours of first two bands A and B corresponds to figures 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and the colour of the third band corresponds to multipliers 10⁰, 10¹, 10², 10³, 10⁴, 10⁵, 10⁶, 10⁷, 10⁸ and 10⁹ respectively. If the colour of the fourth band is gold, the tolerance is 5%, in case the colour is silver, the tolerance is 10%. In case, there is no fourth band, then its tolerance is 20%.

Colour	Number	Multiplier		Tolerance
Black	0	1	Gold	5%
Brown	1	101	Silver	10%
Red	2	102	No Colour	20%
Orange	3	103
Yellow	4	104
Green	5	105
Blue	6	106
Violet	7	107
Grey	8	108
White	9	109

Therefore to assess the value of resistance

1. First two bands from the end indicate the first two significant figures of resistance in ohm.

2. The third band indicates the decimal multiplier.

3. The last band stands for the tolerance in per cent.

Illustration

1. 1st band → Red - 2

2nd band → Red - 2

3rd band → Red - 102

4th band → Silver → 10%

∴ Value of resistance 22 x 10² Ω ± 10% variation

2. 1st band → Yellow → 4

2nd band → Violet → 7

3rd band → Brown → 1

4th band → Gold → 5%

∴ Value of resistance is

47 x 10¹ Ω ± 5% variation

470 Ω ± 5% variation

3. If D band is used as third colour, they indicate a multiplier value of 10^-1 for gold and 10^-2 for Ag band as shown is Fig.

(a) 60 x 10^-1 = 6 Ω

(b) 54 x 10^-2 = 0.54 Ω.