Question

An electric bulb is rated 220 V; 11 W. The resistance of its filament when it glows with a power supply of 220 V is ______.

Options

• 4400 Ω

• 440 Ω

• 400 Ω

• 20 Ω

Answer 1

An electric bulb is rated 220 V; 11 W. The resistance of its filament when it glows with a power supply of 220 V is 4400 Ω.

Explanation:

Given: Power (P) = 11 W

Voltage (V) = 220 V 

V = IR

I = `V/R`

According to Ohm’s law:

P = VI

∴ P = `V^2/R`

∴ R = `(220 xx 220)/11`

= 4400 Ω