Question

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 B_o 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,
the 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)

Answer 1

Answer:pieNQBnotR²

Explanation:

Answer 2

we have to find the magnitude of the angular momentum gained by the coil.

solution : given radius of circular coil = R

number of turns = N

let M is magnetic moment and B is magnetic field.

then torque experienced by the circular coil = M × B.

here M = ANi = πR²Ni and B = B₀

so, torque = πR²Ni B₀

⇒τ dt = πR²NiB₀ dt

⇒dL = πR²NiB₀ dt [ as we know, change in angular momentum with respect to time is torque so τ dt = dL]

⇒dL = πR²NB₀ (idt) = NR²NB₀Q [ idt = Q]

Therefore the correct option is (B)