Bar Magnet

Practice Questions:

Question 1: difficult

A plastic disc of radius R has a charge q uniformly distributed over its surface. If the disc is rotated with a frequency f about its axis. then magnetic dipole moment will be :

1. \[\frac{\pi qfR^{2}}{2}\]

2. πqfR²

3. 2πqfR²

4. 4πqfR²

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Question 2: difficult

A square coil of side ‘a’ carrying current ‘ i ’ and is having one of its side AB parallel to
y-axis and its plane is at angle θ = 30° with x-axis. If a uniform magnetic field B exist in
the region along \[\hat{k}\] direction, then torque due to magnetic force on the coil is:

1. \[\frac{ia^{2}B}{2}\hat{j}\]

2. \[-\frac{ia^{2}B}{\sqrt{2}}\left(-\hat{k}+ \hat{j} \right)\]

3. \[-\frac{ia^{2}B}{2}\hat{j}\]

4. \[\frac{ia^{2}B}{2}\hat{i}\]

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