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# Form 4 Physics Mains Electricity Questions and Answers

An electric heater is made of a wire of resistance 100Ω and connected to a 240V supply. Determine the:
(i) Power rating of the heater.
(ii) Current flowing in the circuit.
(iii) Time taken for the heater to raise the temperature of 200g of water from 23^0C to 95^0C (specific heat capacity of water is
4200J Kg^-1K^-1).
(iv) Cost of using the heater for two hours a day for 30 days. (the power and lighting company charges Kshs 5.00 per kilowatt–hour).

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