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A room heater is rated 400 W, 220 V. If the supply voltage drops to 200 V, what will be the power consumed (approximately)?

Asked in NEET 2026 · Rated bulbs and appliances

(1) 121 W
(2) 200 W
(3) 400 W
(4) 331 W

Answer: (4) 331 W

Step-by-step solution

The resistance is fixed: R=(V₀²)/(P₀).

P=(V²)/R=P₀(V/(V₀))²=400×((200)/(220))².

P=400×0.8264=331 W.

Why the other options are wrong

(1) No single slip gives 121 W; that would need the voltage to fall to 121 V, since P∝ V².
(2) No single slip gives 200 W; halving the power would need the voltage to fall to about (220)/(√2)≈156 V.
(3) This is the rated power, which the heater draws only at its rated 220 V.

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