An equilateral triangular coil of side 10 cm lies in a vertical plane in a horizontal magnetic field 20 mT. When current 0.2 A flows and the plane becomes parallel to B, the torque is √x×10⁻⁵ N·m. Find x.
Physics · Magnetic effect of current
JEE Mains 2021

Question

An equilateral triangular coil of side 10 cm lies in a vertical plane in a horizontal magnetic field 20 mT. When current 0.2 A flows and the plane becomes parallel to B, the torque is √x×10⁻⁵ N·m. Find x.

Physics · Magnetic effect of current

G1 Physics · Accepted Answer

At maximum torque, τ=IAB. Triangle area=(√3/4)(0.1)²=0.0025√3 m². Thus τ=0.2×0.02×0.0025√3=√3×10⁻⁵ N·m. Hence x=3.