Question

A small bulb has a resistance of 2 resistance when switched off. It takes up a current of 0.4 A from a source of 4V and then starts glowing. Calculate (i) the resistance of the bulb when it is glowing and a) Elaborate on the reason for the difference in resistance?​

Answer 1

Answer:

The resistance of the bulb when it is glowing is 10 Ω. The resistance increased because of the increase in temperature.

Explanation:

The resistance of the bulb when it is switched off is 2 Ω.

When switched on,

The current through the bulb, I = 0.4 A

The voltage across the bulb, V = 4 V

∴ The resistance of the bulb. R = V/I

                                                R = 4 / 0.4

                                                R = 10 Ω

There is a change in the resistance of the bulb when it is switched on. When switched on, the temperature of the bulb will increase. This will be according to Joule's law (H = I²Rt). When the temperature increases the resistance will also increase.