JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव JEE PYQ-Magnetic Effects Of Current

  • question_answer
    A charge is spread uniformly over an insulated loop of radius. If it is rotated with an angular velocity\[\omega \] with respect to normal axis then the magnetic moment of the loop is [JEE Main Online 16-4-2018]

    A)  \[A\frac{1}{2}q\omega {{r}^{2}}\]

    B) \[\frac{4}{3}q\omega {{r}^{2}}\]

    C) \[\frac{3}{2}q\omega {{r}^{2}}\]

    D) \[q\omega {{r}^{2}}\]

    Correct Answer: A

    Solution :

    [a] Let us take an element at an angle
    \[\theta \] subtending an angle
    \[d\theta \]
    The charge the element has can be written as
    \[dq=\frac{q}{2\pi }d\theta \]
    We know that\[i=\frac{dq}{dt}=\frac{q}{2\pi }\times \frac{d\theta }{dt}\]
    The time dt can be written as
    \[dt=\frac{d\theta }{w}\]
    Hence\[i=\frac{qw}{2\pi }\]
    magnetic moment = iA
    Hence Manetic moment\[M=\frac{qw}{2\pi }\times \pi {{r}^{2}}=\frac{qw{{r}^{2}}}{2}\]


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