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Question
A student boils water in an electric kettle for 20 minutes. Using the same mains supply he wants to reduce the boiling time of water. To do so should he increase or decrease the length of the heating element? Justify your answer.
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Solution
To reduce the boiling time using the same mains supply, the rate of heat production should be large.
We know that P = V2/R.
Since V is constant, R should be decreased. Since R is directly proportional to l so length should be decreased.
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