Question

The adjacent diagram shows a small magnet placed near a solenoid AB with its north pole N near end A. Current is switched on in the solenoid by pressing the key K. Magnet will get:

(A) Attracted
(B) Repelled
(C) No change
(D) Can’t say

Answer 1

Hint: To answer this question, we need to find out the polarity of the solenoid, with the help of which the nature of force on the magnet will be determined. For finding out the polarity, we have to use the direction of the current flowing in the circuit.

Complete step by step solution:
We know that the current flows out through the positive end of a battery and flows into the negative end. So as the switch in the circuit is closed, the direction of the current in the circuit is as shown in the below diagram.

Now, if we look at the front side of the solenoid, near the magnet, then we can easily observe that the current is flowing in an anticlockwise direction in the loop of the solenoid. So from the right hand rule we get the direction of the magnetic field into the loop or from the end A to the end B of the solenoid. So the polarity of the magnet is as shown is the below figure.

As we can see in the above figure, the north pole of the magnet is in front of the north pole of the solenoid. We know that the like poles repel each other. So the magnet will get repelled when the current is switched on in the circuit.
Hence the correct answer is option B.

Note:
We should not try to involve the use of Lenz's law to answer this question. This is because there is no change in flux involved. Neither the magnet is being moved, nor is the current in the circuit changing its direction. The current in the circuit is due to the battery, which is the direct current of constant magnitude.