Question

A 100 watt 220 volt electric lamp is connected across 110 volt the actual power consumed by the lamp is

Answer 1

P = V2/R

V = 220 V

100 W = 2202/R

R = 2202/100 Ω = 484 Ω.

This is the resistance of the bulb.

V = 110 V,

power consumed = V2/R

= 1102 /484

= 25 W.

Answer 2

Given

power P = 100 watt

Potential difference  = 220 V

We know power P =VI

where V = potential difference

I = current

Thus I = P/V = 100/220 = 0.45 Ampere

Thus actual power = 110 × 0.45 = 50 Watt