Question

A carbon resistor is shown in the figure. Using the colour code, write the value of the resistance.

Answer 1

Hint: We need to understand the colour coding technique used in electrical devices to give the resistance of the material of the wire used. This will help us find the resistance of the resistor given in the question and thus solve the problem.

Complete Solution:
The colour coding is a technique used in electrical devices especially the resistors, which are used to identify the resistance of a given resistor. The manufacturers use this standard coding technique to provide their clients with the idea of the resistance well in advance to carry out experiments or circuit connections with more accuracy.
The manufacturers use this 10-colour code which consists of three or four coloured lines. The first two colours in the band indicate the first two significant figures of the resistance of the resistor and the third band represents the multiplier (ten raised to the number). A fourth band can appear to be gold, silver or colourless. They represent the tolerance of variation of the resistance in percentage as 5, 10 and 20 respectively.
The colours that constitute the first three bands are given by –
Black – 0
Brown – 1
Red – 2
Orange – 3
Yellow – 4
Green – 5
Blue – 6
Violet – 7
Grey – 8
White – 9

In the case given to us, the bands are coloured in order as –
Green – 5, Violet – 7, Red – 2, Colourless – $$20\mathrm{\%}$$
So, the resistance can be given as –
$$(5.7\times {10}^2\pm 20\mathrm{\%})\mathrm{\Omega }$$

i.e., the resistor has a resistance of about 570 ohms.

This is the required solution.

Note:
The colour coding is mainly used in the carbon resistors, which are very small in size. The resistance of these resistors are sometimes difficult to be written on them, so the method of colour coding is used instead as we have seen in this problem.