NEET Sample Paper NEET Sample Test Paper-39

  • question_answer An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from temperature\[\text{20 }\!\!{}^\circ\!\!\text{ C}\]? The temperature of boiling water is\[\text{100 }\!\!{}^\circ\!\!\text{ C}\].

    A)  6.3 min       

    B)  8.4 min

    C)  12.6 min     

    D)  4.2 min

    Correct Answer: A

    Solution :

     Heat evolved due to Joule's effect is used up in boiling water. \[VIt=ms\Delta t\]or \[t=\frac{ms\Delta t}{VI}\] We are given \[I=4A,V=200\,volt,\,m=1\,kg,\] \[\Delta t=(100-20){{\,}^{o}}C,s=4200\,J/kg{{\,}^{o}}C\] \[\therefore \] \[t=\frac{1\times 4200\times 80}{220\times 4}=6.3\,\min \]

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