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1 kg of water, at 20°C, heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of 20 Ω. The rms voltage in the mains is 200 V. Ignoring heat loss from the kettle, time taken for water to evaporate fully, is close to : (Specific heat of water = 4200 J/kg °C, Latent heat of water = 2260 kJ/kg)

1. 10 minutes
2. 22 minutes
3. 3 minutes
4. 16 minutes

Correct answer: 16 minutes

Solution

The correct option is right because the energy required to heat the water to its boiling point and then to evaporate it can be calculated using the specific heat and latent heat values. The power delivered by the kettle can be determined from the voltage and resistance, allowing us to find the total time needed to provide the necessary energy, which results in approximately 16 minutes.

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