Question

A small magnet is moving with constant velocity along the axis of a coil, as shown in the figure. Then correct graph between induced emf $e$ and time $t$ is

• A.
• B.
• C.
• D.

Answer 1

The correct option is D


According to Faraday's Law of electromagnetic induction, an emf is induced in a loop, when there is a flux change. Its value is given by,

$e=-\frac{d\varphi }{dt}$

As, the bar magnet is moving inside the coil, the magnetic field and hence the magnetic flux keeps on increasing with time. Therefore, a negative emf is induced inside the coil.

When the magnet is completely inside the coil, the flux becomes constant and hence induced emf is $0$.

When the magnet moves out of the coil the magnetic flux keeps on decreasing with time and hence a positive emf is induced in the coil.

Therefore, the graph $\left(D\right)$ is correct.