Question

A small circular ring is kept inside a larger loop connected to a switch and a battery as shown. The direction of induced current when the switch is made (i) ON (ii) OFF after was ON for a long time is:
(A)clockwise, anti-clockwise
(B) clockwise, clockwise
(C) anti-clockwise, clockwise
(D) anti-clockwise, anti-clockwise

Answer 1

Lenz Law proposes that the direction of induced current is in such a way that it opposes the change in magnetic flux in the coil. Using, this law we will find out our answers readily. We have to also use the idea of change in flux for the second part.

Complete step by step answer:
(i) We know that current flows from positive terminal to negative terminal.

In the given figure, we can say that when the switch S is closed or ON, the current moves from the positive to negative terminal. And hence the direction is anticlockwise in the larger loop.
A magnetic field is thus set up out of the plane of paper. According to the Lenz Law, we come to a conclusion that the induced current that is set up is to oppose the change in flux in the larger loop. In order to do so, a magnetic field is to be set up in the plane of paper which can be made when there is a current induced in the smaller coil. So, the current in the smaller loop is in clockwise direction.
(ii)

When the current is being kept OFF or open after a long time then the magnetic field is being reduced. Hence the change in magnetic flux is also decreasing. In order to cope up with the reducing flux an induced current is set up in the smaller field whose direction is clockwise.
So, the correct option is (A).

Note: When the switch is open or OFF, then there was no magnetic field and hence no induced emf developed.it must be noted that the induced emf always opposes the change in the magnetic flux in a coil. Magnetic flux is defined as total magnetic field that passes through a given area.