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A bulb rated at 220 V, 1000 W is connected to a 110 V supply. The electrical power it will draw is

1. 750 W
2. 500 W
3. 250 W
4. 1000 W

Correct answer: 250 W

Solution

R = 220^2/1000 = 48.4 ohm. At 110 V, P = 110^2/48.4 = 250 W.

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