NEET Physics Electro Magnetic Induction NEET PYQ-Electro Magnetic Induction

  • question_answer
    Two coils of self-inductances 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is:            [AIPMT (S) 2006]

    A)        10 mH              

    B)       6 mH

    C)  4 mH     

    D)                   16 mH

    Correct Answer: C

    Solution :

    When the total flux associated with one coil links with the other i.e., a case of maximum flux linkage, then
                            \[{{M}_{12}}=\frac{{{N}_{2}}\,{{\phi }_{{{B}_{2}}}}}{{{i}_{1}}}\] and \[{{M}_{21}}=\frac{{{N}_{1}}\,{{\phi }_{{{B}_{1}}}}}{{{i}_{2}}}\]
                Similarly,  \[{{L}_{1}}=\frac{{{N}_{1}}\,{{\phi }_{{{B}_{1}}}}}{{{i}_{1}}}\] and \[{{L}_{2}}=\frac{{{N}_{2}}\,{{\phi }_{{{B}_{2}}}}}{{{i}_{2}}}\]
                If all the flux of coil 2 links coil 1 and vice-versa then
                            \[{{\phi }_{{{B}_{2}}}}={{\phi }_{{{B}_{2}}}}\]
                Since, \[{{M}_{12}}={{M}_{21}}=M,\] hence we have
                            \[{{M}_{12}}\,{{M}_{21}}={{M}^{2}}=\frac{{{N}_{1}}\,{{N}_{2}}\,{{\phi }_{{{B}_{1}}}}\,{{\phi }_{{{B}_{2}}}}}{{{i}_{1}}\,{{i}_{2}}}={{L}_{1}}\,{{L}_{2}}\]
    \[\therefore \]      \[{{M}_{mas}}=\sqrt{{{L}_{1}}\,{{L}_{2}}}\]
    Given,   \[{{L}_{1}}=2\,mH,\,\,{{L}_{2}}=8\,mH\]
    \[\therefore \]      \[{{M}_{\max }}=\sqrt{2\times 8}=\sqrt{16}=4\,mH\]


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