NEET Sample Paper NEET Sample Test Paper-12

  • 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

    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 \[{{\phi }_{{{B}_{2}}}}={{\phi }_{{{B}_{1}}}}\] Since,\[{{M}_{12}}={{M}_{21}}=M,\] hence we have \[{{M}_{12}}{{M}_{21}}={{M}^{2}}=\frac{{{N}_{1}}{{N}_{2}}{{\phi }_{{{B}_{1}}}}{{\phi }_{{{B}_{2}}}}}{{{i}_{1}}{{i}_{2}}}={{L}_{1}}{{L}_{2}}\] \[{{M}_{\max }}=\sqrt{{{L}_{1}}{{L}_{2}}}\] Given, \[{{L}_{1}}=2\,mH,\,{{L}_{2}}=8\,mH\] \[{{M}_{ax}}=\sqrt{2\times 8}=\sqrt{16}=4\,mH\]


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