Question

A magnet is suspended from a spring as shown in the diagram. When it oscillates, the magnet moves in and out of the coil. The coil is connected to a galvanometer $G$. Then, as the magnet oscillates -

Consider the loss of energy due to various factors.

• A. $G$ shows no deflection.
• B. $G$ shows deflection to the left and right, but the amplitude steadily decreases.
• C. $G$ shows deflection to the left and right with constant amplitude.
• D. $G$ shows deflection on one side only.

Answer 1

The correct option is B $G$ shows deflection to the left and right, but the amplitude steadily decreases.


As the magnet approaches the coil, the flux through the coil changes and current is induced in one direction.

Also, as the magnet moves away from the coil, the flux through the coil changes and current is induced in the opposite direction.

Therefore, $G$ shows the deflection to the left and right.

Further, due to eddy current losses, the amplitude of the magnet's SHM decreases, thus its maximum velocity also decreases. Therefore, amplitude of deflection of $G$ also decreases.