A) 12.6 min
B) 4.2 min
C) 6.3 min
D) 8.4 min
Correct Answer: C
Solution :
Heat taken by water when its temperature changes from \[{{20}^{o}}C\]to \[{{100}^{o}}C\]is \[{{H}_{1}}=mc({{\theta }_{2}}-{{\theta }_{1}})=1000\times 1\times (100-20)cal\] \[=1000\times 80\times 4.2J\] Heat produced in time t due to current in resistor is \[{{H}_{2}}=Vit=220\times 4\times t\,J\] According to question, \[220\times 4\times t=1000\times 80\times 4.2\] or \[t=\frac{1000\times 80\times 4.2}{220\times 4}=381.8s=6.3\min \]
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