A room heater is rated 400 W at 220 V. If its supply voltage falls to 200 V and the heater resistance stays constant, what is the approximate power consumed?
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Question

A room heater is rated 400 W at 220 V. If its supply voltage falls to 200 V and the heater resistance stays constant, what is the approximate power consumed?

G1 Physics · Accepted Answer

Step 1: Rated power P(rated) = V(rated)²/R, so R = V(rated)²/P(rated). Step 2: R = 220²/400 = 48400/400 = 121 Ω. Step 3: At supply voltage V = 200 V, power P = V²/R = 200²/121. Step 4: P = 40000/121 ≈ 330.58 W ≈ 331 W. Final answer: 331 W (Option C).