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Heat required to raise the temperature of 1 kg water from 20°C to 100°C is given by Q = mSΔθ = (1 × 4200 × 80) J. Power of kettle (P) = VIt = (220 × 4) W. Time taken = Q / P = 1 × 4200 × 80 / 220 × 4 = 381.81 sec = 6.36 min.

1. Heat required to raise the temperature of 1 kg water from 20°C to 100°C is given by Q = mSΔθ = (1 × 4200 × 80) J.
2. Power of kettle (P) = VIt = (220 × 4) W.
3. Time taken = Q / P = 1 × 4200 × 80 / 220 × 4 = 381.81 sec = 6.36 min.
4. None of the above.

Correct answer: None of the above.

Solution

The calculation of time taken is incorrect because the formula Q / P should be used with proper parentheses. The correct calculation is Q / (P) = (1 × 4200 × 80) / (220 × 4). None of the options are entirely correct.

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