A square loop is made of four rods, each of mass m and length ℓ, carrying current i in uniform magnetic field B as shown. It can rotate about axis P₁P₂ and is released from rest at t=0. Which statements are correct?

Question

G1 Physics · Accepted Answer

Magnetic moment of the square is μ=iℓ². Using τ=μB sinφ and the square-frame moment of inertia about P₁P₂, the initial α evaluates to 3Bi/(2m). Energy integration gives the stated ω at 30°, the torque at 60° is iBℓ²/2, and since τ∝cos(rotation angle), α decreases continuously to zero by 90°. Hence A,B,C,D.