An electric heater of resistance 8 Ω draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater.

Rate of generating heat is equal to the power used by the heater. By Joule's Law of heating, P=I²R = 15² × 8 = 1800 W. Hence, the rate of generation of heat is 1800 W. Total amount of heat generated, E = Pt = 1800 × 2 = 3.6 kWh