JEE Main & Advanced Physics Electro Magnetic Induction Question Bank Static EMI

  • question_answer
    Two coils of self-inductance \[{{L}_{1}}\] and \[{{L}_{2}}\] are placed closer to each other so that total flux in one coil is completely linked with other. If \[M\] is mutual inductance between them, then [DCE 2002]

    A)            \[M={{L}_{1}}{{L}_{2}}\]  

    B)            \[M={{L}_{1}}/{{L}_{2}}\]

    C)            \[M=\sqrt{{{L}_{1}}{{L}_{2}}}\]                                        

    D)            \[M={{({{L}_{1}}{{L}_{2}})}^{2}}\]

    Correct Answer: C

    Solution :

                       \[M=-\frac{{{e}_{2}}}{d{{i}_{1}}/dt}=-\frac{{{e}_{1}}}{d{{i}_{2}}/dt}\]                    Also \[{{e}_{1}}=-{{L}_{1}}\frac{d{{i}_{1}}}{dt}.{{e}_{2}}=-{{L}_{2}}\frac{d{{i}_{2}}}{dt}\]            \[{{M}^{2}}=\frac{{{e}_{1}}{{e}_{2}}}{\left( \frac{d{{i}_{1}}}{dt} \right)\ \left( \frac{d{{i}_{2}}}{dt} \right)}={{L}_{1}}{{L}_{2}}\Rightarrow M=\sqrt{{{L}_{1}}{{L}_{2}}}\]


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