Practice portal › Current Electricity › Electrical Energy and Power

A light bulb is rated at 100 W for a 220 V supply. The resistance of the bulb is ______ ohm.

Asked in GSEB Board July 2021 · Rated bulbs and appliances

• (1) 484
• (2) 440
• (3) 220
• (4) 2200

Step-by-step solution

Why the other options are wrong

• (2) Rounds the current P/V=(100)/(220)=0.45 A up to 0.5 A and then takes (220)/(0.5)=440 Ω. With the exact current the resistance is 484 Ω.
• (3) No single slip gives 220 Ω; it just repeats the voltage. Check: 220 Ω on 220 V would draw 1 A and dissipate 220 W, more than twice the rating.
• (4) No single slip gives 2200 Ω. Check: on 220 V it would draw only 0.1 A and dissipate 22 W.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.