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QJEEAdv20Ph020c: JEE Advanced 2020 Physics - Class 12 JEEAdv20Ph020c Solution: A circular coil of radius R and N turns has negligible…

A circular coil of radius R and N turns has negligible resistance. As shown in the schematic figure, its two ends are connected to two wires and it is hanging by those wires with its plane being vertical. The wires are connected to a capacitor with charge Q through a switch. The coil is in a horizontal uniform magnetic field Bo parallel to the plane of the coil. When the switch is closed, the capacitor gets discharged through the coil in a very short time. By the time the capacitor is discharged fully, magnitude of the angular momentum gained by the coil will be (assume that the discharge time is so short that the coil has hardly rotated during this time) JEE Advanced 2020 Paper 1 Offline Physics - Magnetism Question 37 English

Multiple Choice Options

  • A π2NQB0R2{\pi \over 2}NQ{B_0}{R^2}
  • B πNQB0R2\pi NQ{B_0}{R^2}
  • C 2πNQB0R22\pi NQ{B_0}{R^2}
  • D 4πNQB0R24\pi NQ{B_0}{R^2}

Step-by-Step Verified Solution

Torque experienced by circular loop = M ×\times B

where, M is magnetic moment and B is magnetic field.

∴\therefore τ\tau = i π\pi R2NB0

(at the instant shown θ\theta = π\pi /2)

∴\therefore τ\tau dt = dL = i π\pi R2NB0dt

= Q π\pi R2NB0 ( ∵\because idt = Q)

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