Question

A coil of wire is connected to a voltmeter. A bar magnet is quickly inserted into the coil of wire and then quickly removed.

Describe how the voltmeter reading changes before the magnet is inserted, while it is being inserted, while it is being removed and after it has been removed.

Answer 1

Before inserting the magnet, the current flowing through the the coil will be constant and hence the reading of the voltmeter will also be constant.

Depending on the orientation of the coil, The induced current will either be in the direction of the current already flowing or opposite to the initial direction. Hence the current flowing through the coil will either increase or decrease when the magnet is inserted. Let's say that the current increases.

When the bar magnet is removed, it moves in the direction opposite to the direction in the previous case. Hence the direction of induced current will be opposite to the previous case. As we considered that the current will decrease in the previous case, it will increase in this case.

After the bar magnet is removed the current again becomes constant and has the same value as that in the beginning.