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Heater of an electric kettle is made of a wire of length L and diameter d. It takes 4 minutes to raise the temperature of 0.5 kg water by 40 K. This heater is replaced by a new heater having two wires of the same material, each of length L and diameter 2 d. The way these wires are connected is given in the options. How much time in minutes will it take to raise the temperature of the same amount of water by 40 K ?
In Series:
Each wire has resistance R′ = R/4.
The total resistance in series is
2R/4 = R/2, increasing power by 2 times.
Heating time reduces to 4/2 = 2 min.
Correct answer: (b) 2 if wires are in series.
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