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JEE Mains · Physics · STD 12 - Moving charges and magnetism
  • JEE Mains 2019
  • Hard
  • MCQ

A circular coil having \(N\,turns\) and radius \(r\) carries a current. It is held in the \(XZ\) plane in a magnetic field \(B\hat i\) . The torque on the coil due to the magnetic field is

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Answer & Solution

Correct Answer

(D) \({B\pi {r^2}IN}\)

Step-by-step Solution

Detailed explanation

\( \text { Magnetic moment of coil } =\mathrm{NIA} \hat{\mathrm{j}}\)

\(=\mathrm{Nl}\left(\pi \mathrm{r}^{2}\right) \hat{\mathrm{j}} \)

Torque on loop (coil) \(=\overline{\mathrm{M}} \times \overline{\mathrm{B}}\)

\(=\mathrm{Nl}\left(\pi \mathrm{r}^{2}\right) \mathrm{B} \sin 90^{\circ}(-\hat{\mathrm{k}})\)

\(=\mathrm{NI} \pi \mathrm{r}^{2} \mathrm{B}(-\hat{\mathrm{k}})\)

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