A conducting ring is placed near a solenoid as shown in Fig.3.21. Find the direction of the induced current in the ring.
(a) At the instant the switch in the circuit containing the solenoid is closed.
(b) After the switch has been closed for a long time.
(c) At the instant the switch is opened.

Explanation

(a) As the switch is closed, the situation changes from one in which no magnetic flux passes through the ring to the one in which flux passes through the ring in the direction shown. The induced current flows in the aniclockwise sense as seen from the side on which the solenoid lies.
(b) When the switch has been closed for a long time, no change in the magnetic flux through the loop occurs, hence, no current is induced in the loop.

( c) When the switch is opened, flux in the direction shown above. Hence current will be opposite to teh diretion of situation (a), i.e., in clockwise direction.