Question

A short bar magnet passes at a steady speed right through a long solenoid. A galvanometer is connected across the solenoid. Which graph best represents the variation of the galvanometer deflection $\theta$ with time?

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

As we move the magnet towards the coil, the flux would increase to a certain value.

The direction of induced current will be such that the north pole will be formed in the solenoid at the entry end of the solenoid, so as to oppose the magnet while it enters the solenoid.

Once the bar magnet enters into the solenoid, the induced current falls down, and when the bar magnet is completely inside the solenoid, the induced current becomes zero.

Now, when the bar magnet starts leaving the solenoid, then the exit end of the solenoid becomes north and the direction of induced current becomes negative.

The induced current increases to a certain extent in the negative direction and then falls to zero, when it is completely outside the solenoid.

Therefore, the correct graph is:



Hence, option ($A$) is the correct answer.