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NEET Physics Thermometry, Calorimetry & Thermal Expansion NEET PYQ-Thermometry, Calorimetry and Thermal Expansion

  • 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\[20\,{}^\circ C\]? The temperature of boiling water is \[100\,{}^\circ C\].                                       [AIPMPT (S) 2008]

    A)  6.3 min      

    B)       8.4 min

    C)  12.6mm        

    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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