A closely wound circular coil has 20 turns, each of radius 5 cm. Its magnetic moment is \(0.314\ \mathrm{A\,m^2}\). The current in the coil is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 2 A
The magnetic moment of a coil of \(N\) turns is \(m=NIA\). For a circular coil the area is \(A=\pi r^2\), with \(r=0.05\ \mathrm{m}\).
\( \begin{aligned} I &= \frac{m}{N\pi r^2} \\ &= \frac{0.314}{20\times3.14\times25\times10^{-4}} \\ &= \frac{0.314}{0.157} \\ &= 2\ \mathrm{A} \end{aligned} \)
NCERT (2026-27):
Torque on a rectangular current loop in a uniform magnetic field – “If the loop has N closely wound turns, the expression for torque, … still holds, with”
\( m=NIA \)\( \qquad (4.24) \)