The heater element of an electric kettle has a constant resistance of 100 Ω ohm and the applied voltage is 250 V. Calculate the time taken to raise the temperature of one litre of water from 15°C to 90°C assuming that 85% of the power input to the kettle is usefully employed. If the
water equivalent of the kettle is 100 g. find how long will it take to raise a second litre of water through the same temperature range immediately after the first.