A bar magnet is held at a right angle to a uniform magnetic field. The couple acting on the magnet is to be halved by rotating it from this position. The angle of rotation is

Question

A bar magnet is held at a right angle to a uniform magnetic field. The couple acting on the magnet is to be halved by rotating it from this position. The angle of rotation is, 60 °, 45 °, 30 °, 75 °

MARKS App · Accepted Answer

Torque, τ = MB sin ⁡ θ Where θ = 90 ° ∴ τ = MB Given, τ 2 = 1 2 τ 1 ∴ MB sin ⁡ θ = 1 2 MB ∴ sin θ ⁡ = 1 2 ⇒ θ = 30 ° Angle of rotation = 90 ° - 30 ° = 60 °

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