Question
An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from temperature 200 C? The temperature boiling water is 100o C.
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6.3 min
-
8.4 min
-
12.6 min
-
4.2 min
Solution
A.
6.3 min
Heat is evolved due to joule's effect is used up in boiling water.
such as
Vlt = msΔt
t = msΔt/VI
Putting under given values
I= 4A, V= 220 volt, m =1 kg,
Δt = (100-20)oC, s = 4200 J/kgo C
t = 1 x 4200 x 80 / 220 x 4 = 6.3 min
