A magnet of magnetic moment \(2\,\mathrm{J\,T^{-1}}\) is kept along a magnetic field of strength \(0.2\,\mathrm{T}\), the work done to turn it in the opposite direction to the field, will be
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \(0.8\,\mathrm{J}\)
The potential energy of a magnetic dipole in a uniform field is \( U = -MB\cos\theta \). The work done in turning it is the change in this energy.
Along the field \( \theta = 0^\circ \); opposite to the field \( \theta = 180^\circ \).
\( \displaystyle W = U_{180^\circ} - U_{0^\circ} = -MB\cos 180^\circ - (-MB\cos 0^\circ) \)
\( \displaystyle W = 2MB \)
\( \displaystyle W = 2 \times 2\,\mathrm{J\,T^{-1}} \times 0.2\,\mathrm{T} \)
\( \displaystyle W = 0.8\,\mathrm{J} \)
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
