A) 6.3 min
B) 8.4 min
C) 12.6 min
D) 4.2 min
Correct Answer: A
Solution :
Key Idea: Heat evolved due to Joule's effect is used up in boiling water. As per key idea\[VIt=ms\Delta t\] or\[t=\frac{ms\Delta t}{VI}\] Putting under given values \[I=4A,V=220\]volt,\[m=1kg,\] \[\Delta t={{(100-20)}^{o}}C,s=4200J/k{{g}^{o}}C\] \[\therefore \]\[t=\frac{1\times 4200\times 80}{220\times 4}=6.3\min \]
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