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In India electricity is supplied for domestic use at 220 V. It is supplied at 110 V in USA. If the resistance of a 60 W bulb for use in India is R, the resistance of a 60 W bulb for use in USA will be

1. R/2
2. R
3. 2R
4. R/4

Correct answer: R/2

Solution

The power of a bulb is given by P = V²/R. For the same power (60 W), the resistance is inversely proportional to the square of the voltage. Since the voltage in the USA is half that in India (110 V vs. 220 V), the resistance in the USA will be R/2.

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