JEE Main & Advanced Physics Electro Magnetic Induction Question Bank Critical Thinking

  • question_answer
    Shown in the figure is a circular loop of radius r and resistance R. A variable magnetic field of induction \[B={{B}_{0}}{{e}^{-t}}\] is established inside the coil. If the key (K) is closed, the electrical power developed right after closing the switch is equal to

    A)             \[\frac{B_{0}^{2}\pi {{r}^{2}}}{R}\]                                              

    B)             \[\frac{{{B}_{0}}10{{r}^{3}}}{R}\]

    C)             \[\frac{B_{0}^{2}{{\pi }^{2}}{{r}^{4}}R}{5}\]                             

    D)             \[\frac{B_{0}^{2}{{\pi }^{2}}{{r}^{4}}}{R}\]

    Correct Answer: D

    Solution :

                       \[P=\frac{{{e}^{2}}}{R};\ \ e=-\frac{d}{dt}(BA)=A\frac{d}{dt}({{B}_{o}}{{e}^{-t}})=A{{B}_{o}}{{e}^{-t}}\]                    \[\Rightarrow P=\frac{1}{R}{{(A{{B}_{o}}{{e}^{-t}})}^{2}}=\frac{{{A}^{2}}B_{o}^{2}{{e}^{-2t}}}{R}\]                    At the time of starting t = 0 so \[P=\frac{{{A}^{2}}B_{o}^{2}}{R}\]             \[\Rightarrow P=\frac{{{(\pi {{r}^{2}})}^{2}}B_{o}^{2}}{R}=\frac{B_{o}^{2}{{\pi }^{2}}{{r}^{4}}}{R}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner