JEE Main & Advanced Sample Paper JEE Main - Mock Test - 12

  • question_answer
    The magnetic flux \[\phi \]through a stationary loop of wire having a resistance R varies with time as \[\phi =a{{t}^{2}}+bt\](a and b are positive constants). The average emf and the total charge flowing in the loop in the time interval t = 0 to \[t=\tau \] respectively are

    A) \[a\tau +b,\frac{a{{\tau }^{2}}+b\tau }{R}\]

    B) \[a\tau +b,\frac{a{{\tau }^{2}}+b\tau }{2R}\]

    C) \[\frac{a\tau +b}{2},\frac{a{{\tau }^{2}}+b\tau }{R}\]

    D) \[2(a\tau +b),\frac{a{{\tau }^{2}}+b\tau }{2R}\]

    Correct Answer: A

    Solution :

    [a]: Given:\[\phi =a{{t}^{2}}+bt\] The magnitude of induced emf is \[\varepsilon =\frac{d\phi }{dt}=\frac{d}{dt}(a{{t}^{2}}+bt)=2at+b\] Current flowing,\[I=\frac{|\varepsilon |}{R}=\frac{2at+b}{R}\] Average emf\[=\frac{\int\limits_{0}^{\tau }{\varepsilon dt}}{\int\limits_{0}^{\tau }{dt}}=\frac{\int\limits_{0}^{\tau }{(2at+b)dt}}{\tau }=a\tau +b\] Total charge flowing, \[q=\int_{0}^{\tau }{Idt}=\int\limits_{0}^{\tau }{\frac{(2at+b)}{R}.dt=\frac{a{{\tau }^{2}}+b\tau }{R}}\]


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