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12th Class Physics Magnetism Question Bank Case Based (MCQs) - Moving Charges and Magnetism

  • question_answer
                    The magnetic field due to a current in a straight wire segment of length L at a point on its perpendicular bisector at a distance r (r > > L):

    A) decreasea as \[\frac{1}{r}\]

    B) decreases as \[\frac{1}{{{r}^{2}}}\]

    C) decreases as \[\frac{1}{{{r}^{3}}}\]      

    D) approaches a finite limit as \[r\to \infty \]

    Correct Answer: B

    Solution :

    (b) decreases as \[\frac{1}{{{r}^{2}}}\]. From Biot-savart's law.     \[dB=\frac{{{\mu }_{0}}}{4\pi }\frac{Idl}{{{r}^{2}}}i.e.\,dB\propto \frac{1}{{{r}^{2}}}\]


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