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AFMC AFMC Solved Paper-2002

  • question_answer
    A coil having 100 turns and area of 0.001 m2 is free to rotate about an axis, the coil is placed perpendicular to a magnetic field of Wb /m2. If the coil is rotated rapidly through an angle of 180°, how much charge will flow through the coil? The resistance of the coil is 100.

    A) 0.02 C                                   

    B) 0.04 C

    C) 0.08 C                                   

    D) 0.01 C

    Correct Answer: A

    Solution :

    Key Idea: Maximum flux is linked with coil when its plane is perpendicular to magnetic field. The flux \[(o|)\]linked with coil is \[o|=NAB\,cos\theta \] When plane of coil is perpendicular to field       \[\theta ={{90}^{o}}\] \[\therefore \]    \[\text{o }\!\!|\!\!\text{ }=\text{NAB}\] Change in flux when rotating the coil by \[{{180}^{o}}\]is given by \[d\text{o }\!\!|\!\!\text{ =NAB-(-NAB) = 2 NAB}\] Also, from Faraday's law of electromagnetic induction, we have \[e=-\frac{d\text{o}|}{dt}\]where, \[e=IR,\,I\]is current and R is resistance. \[\therefore \]      \[IR=\frac{d\text{o }\!\!|\!\!\text{ }}{dt}\] \[\therefore \]   Charge \[Idt=\text{o }\!\!|\!\!\text{ /R}\] or    \[\text{Charge}=\frac{2\,NAB}{R}\] \[\therefore \]    Induced charge \[=\frac{2\times 100\times 0.001\times 1}{10}\]


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