JEE Main & Advanced Sample Paper JEE Main Sample Paper-11

  • question_answer
    A metal rod of length 1 m is rotated about one of its ends in plane at right angles to a field of inductance \[2.5\times {{10}^{-3}}\]\[Wb/{{m}^{2}}\]. If it makes 1800 revolutions/min, calculate induced e.m.f. between its ends.

    A)  0.321                   

    B)  0.471

    C)  0.235                   

    D)  0.512

    Correct Answer: B

    Solution :

    Given: \[\ell =1m,B=5\times {{10}^{-3}}\text{Wb/}{{\text{m}}^{\text{2}}}\] \[f=\frac{1800}{60}=30\]rotations/sec In one rotation, the moving rod of the metal traces a circle of radius \[r=\ell \] \[\therefore \]Area swept in one rotation\[=\pi {{r}^{2}}\] \[\frac{d\phi }{dt}=\frac{d}{dt}(BA)=B.\frac{dA}{dt}=\frac{B\pi {{r}^{2}}}{T}\] \[=Bf\pi {{r}^{2}}=(5\times {{10}^{-3}})\times 3.14\times 30\times 1=0.471\,\text{V}\] \[\therefore \] e.m.f. induced in a metal rod = 0.471 V


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