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Question
An electric immersion heater is rated 1250 W. Calculate the time in which it will heat 20 kg of water at 5°C to 65°C.
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Solution
Power supplied by an electric heater (VI) = 1250 W
θ1 = Initial temperature = 5°C
m = Mass of water = 20 kg
θ2 = Final temperature = 65°C
c = specific heat capacity by heater = Heat gained by water ...(Law of calorimeter)
VIt = mc (θ2 - θ1) .....(Q = VI t)
1250 t = 20 × 4200 × 60 ....[(65°C - 5°C = 60°C)]
1250 t = 5040000
t = 40325 seconds
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