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Monday, May 19, 2008

Q) An electric kettle takes 4A current at 220V. How much time will it take to boil 1 kg of water from temperature 20 degrees C ? (The temperature of boiling water is 100 degrees C).


A)
P = IV = 880 Watts

P = work / time = 880 joules per sec

Q = m.c.del T
c is 4200 J per kg per K for water

Q = 1*4200* 80 = 336000

Time = Q / W = 336000 / 880 = 381.81 seconds

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