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How long will a 836 W electric heater take to raise the temperature of 1 litre of water from 10°C to 40°C?

1. 150 s
2. 100 s
3. 50 s
4. 200 s

Correct answer: 150 s

Solution

Heat needed Q = m c deltaT = 1 kg * 4186 J/kgK * 30 K = 125580 J. Time t = Q/P = 125580/836 ~ 150 s.

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