Question

A small bulb has a resistance of 2 ohm when cold . It takes up a current of 0.4 A from a source of 4v and then start glowing . Calculate the resistance of the bulb when it is glowing and Elaborate on the reason for the difference in resistance

Answer 1

Resistance = R = 2 Ohm

Current = I = 0.4 A

V = 4 V

Now,

V = IR'

4 = 0.4 R'

R' = 10 Ohm

Therefore,

New Resistance = R' = 10 Ohm.

This is because when it was cold. It means there was no current then its resistance was 2 Ohm but when current was supplied it changed its temperature.

Therefore, there is variation in resistance.