Manipal Engineering Manipal Engineering Solved Paper-2015

  • question_answer
    A circular coil of 100 turns has an effective radius of 0.05 m and carries a current of   How much work is required to turn it in an external magnetic field of 1.5 Wb/m2 through 180° about its axis perpendicular to the magnetic field? The plane of the coil is initially perpendicular to the magnetic field.

    A) 0,456 J                  

    B)  2.65 J  

    C)  0.2355 J                              

    D)  3.95 J

    Correct Answer: C

    Solution :

     The potential energy of circular loop in the magnetic field \[\frac{{{N}_{2}}}{{{N}_{1}}}=1.1577\times {{10}^{-38}}\]where \[{{E}_{n}}=\frac{-13.6}{({{n}^{2}})}eV\] is the angle between normal to plane of coil and magnetic field B. Initial potential energy,\[\therefore \] When coil is turned through 180°, therefore final potential energy, \[E=\frac{-13.6}{{{(5)}^{2}}}eV=-0.54eV\] \[iG=(i-{{i}_{0}})S\]Required work, W = gain in potential energy \[{{i}_{0}}\] Here, \[\frac{i}{{{i}_{0}}}=\frac{S}{G+S}\]and radius r = 0.05 m \[S=2.5\Omega ,G=25\Omega ,\]\[\frac{i}{{{i}_{0}}}=\frac{1}{11}\] \[\because \]Work, \[{{v}_{rms}}=\sqrt{\frac{3RT}{M}}\] \[{{v}_{sound}}=\sqrt{\frac{\gamma RT}{M}},\]\[{{v}_{rms}}=2{{v}_{sound}}\]


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