JEE Main & Advanced Sample Paper JEE Main - Mock Test - 20

  • question_answer
    A magnetic flux through a stationary loop with a resistance R varies during the time interval \[\tau \]as \[\phi =at(\tau -t)\]. Determine the amount of heat generated in the loop during that time. The inductance of the loop is to be neglected,

    A) \[\frac{a{{\tau }^{3}}}{3R}\]              

    B) \[\frac{{{a}^{2}}{{\tau }^{3}}}{3R}\]

    C) \[\frac{{{a}^{3}}{{\tau }^{3}}}{3R}\]                       

    D) \[\frac{a\tau }{3R}\]

    Correct Answer: B

    Solution :

    [b]: Induced emf, \[E=-\frac{d\phi }{dt}=2at-a\tau ,\] Current through the loop,\[I=\frac{E}{R}=\frac{2at-a\tau }{R}\]?(i) dQ = amount of heat generated in a time\[dt={{I}^{2}}Rdt\] \[\therefore \]Total amount of heat generated in that time is \[Q=\int_{{}}^{{}}{dQ}=\int\limits_{0}^{\tau }{{{I}^{2}}Rdt}=\int\limits_{0}^{\tau }{\frac{{{(2at-a\tau )}^{2}}Rdt}{{{R}^{2}}}}\](Using (i)) By solving integration, we get\[Q\approx \frac{{{a}^{2}}{{\tau }^{3}}}{3R}\]


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