A cylindrical bar magnet is kept along the axis of circular coil. If the magnet is rotated about its axis, then :
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → no current will be induced in the coil
By Faraday's law, an emf (and so a current) is induced in a coil only when the magnetic flux linked with it changes.
\( \displaystyle \varepsilon = -\frac{d\Phi_B}{dt} \)
A cylindrical bar magnet is symmetric about its own axis, and here that axis is also the axis of the coil. Rotating the magnet about this axis leaves its field pattern unchanged at every point of the coil. The flux through the coil is therefore constant, \( d\Phi_B/dt = 0 \), so no emf and no current are induced. Flux is still linked with the coil; it is merely constant.
NCERT (2026-27):
Faraday’s Law of Induction – “… The magnitude of the induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit. Mathematically, the induced emf is given by
\( \displaystyle \varepsilon = -\frac{d\Phi_B}{dt} \qquad (6.3) \)”