Question

In the following diagram an arrow shows the motion of the coil towards the bar magnet.

(1) State in which direction the current flows: A to B or B to A?
(2) Name the law used to come to the conclusion.

Answer 1

Hint: As the first step, you could clearly understand the situation that, as the coil is moved towards the bar magnet, there is a current being induced in the coil. So, for finding the direction of this current, you could recall Lenz's law. From the statement of Lenz’s law, you will get a condition to be satisfied and hence the direction of induced current.

Complete solution:
In the question, we are given a bar magnet and a coil. The coil is being moved towards the bar magnet as shown in the figure given above. We have to find the direction of the current flow in the coil, whether from A to B or from B to A. Also, we have brief the law that we used to make the particular conclusion.
(1) The direction of the current will be from A to B.
(2) The law that is used to make this conclusion on the direction of current is Lenz's law. In order to understand how we made the conclusion, we should understand Lenz’s law clearly.

Lenz's law states that when there is a changing magnetic field an electric current is induced in a conductor. This induced current further creates a magnetic field. The direction of the induced emf is such that it opposes the changing magnetic field that created it.

So as the coil is subjected to change in magnetic field, the direction of the induced current is such that it repels the bar magnet. So, the right end of the coil acts as the North Pole, that is, the current will be in an anti-clockwise direction in the coil. Hence, the current will be directed from A to B.

Note:
It could be called a qualitative law as it just gives information about the direction of the current but no clue about its magnitude. We could consider this law analogous law to Newton’s third law in classical mechanics which states that for every action there is an equal and opposite reaction.