Question

Figure shows a bar magnet being pushed toward a conducting loop from below, along the axis of the loop. What is the direction of an induced current in the loop? Explain.

Answer 1

Concepts and reason

The concept required to solve this problem is Lenz’s law.

Initially, use the properties of bar magnet and find the direction of applied magnetic flux. Then use the Lenz’s law to find the direction of the current.

Fundamentals

The properties of magnetic field due to bar magnet are as follows:

1. The magnetic field lines emerge out of North Pole and ends at South pole of the magnet.

2. The magnetic field strength is more as we go closer to the poles.

Lenz’s law states that the current induced in a conducting material by changing magnetic flux will create a magnetic field exactly opposite to the change in the applied field.

The right-hand thumb rule gives the direction of magnetic field due to a current loop is given by the thumb if fingers curl in the direction of magnetic field or vice versa.

The bar magnet is being pushed toward a conducting loop. The magnetic field lines emerge out from the north pole of the magnet. The magnetic field is in upward direction. The magnet also moves in the upward direction. The magnetic field strength is more near the poles. So, as the magnet’s north pole approaches the loop, the magnetic field through the conducting loop increases. The magnetic flux through the loop is increasing in the upward direction.

The magnetic flux is increasing in the upwards direction as the bar magnet is going closer to the loop. From the Lenz’s law, the induced magnetic flux opposes the increase in the magnetic flux. So, the magnetic flux is induced in the downward direction. From the right-hand rule, the thumb points in the downward direction so the fingers curl in clockwise direction or the induced current is in clockwise direction.

Ans:

The induced current is clockwise.