Question

Predict the direction of induced current in metal rings 1 and 2 when current $I$ in the wire is steadily decreasing.

Answer 1

Hint: Induced current or magnetic field, we will figure out these problems using Maxwell’s right hand thumb rule. Once we find out the direction of the magnetic field we can predict the direction of induced electro-motive force or induced current. We will also use Lenz’s law to figure out the north-pole and south-pole after electromagnetic induction.

Complete step by step answer:
We can find the direction of the magnetic field produced by a current carrying conductor by using Maxwell’s cork-screw rule. As per this rule if we hold a current carrying conductor in our right hand with an erect thumb, when the thumb is pointing towards the direction of electric current, then the direction of our other fingers will be the direction of the generated magnetic field by the conductor.
In the given diagram, the direction of magnetic field for the ring-1, by using right hand thumb rule, is perpendicular to the plane of paper/screen and directed inwards. This magnetic field will generate a magnetic flux inside the ring-1 which in turn will induce an emf or current in the ring.
Lenz’s law states that the direction of induced emf or current should be such that it opposes the very cause which produces it. If the current is steadily decreasing, so will decrease the strength of the magnetic field. (Generated magnetic field intensity is directly proportional to current flowing)
So in order to oppose the decreasing magnetic field intensity, the upper face of the ring will behave as south-pole. And we know induced south-pole in a ring means current is flowing in clockwise manner.
Hence the direction of current in ring-1 will be clockwise.
Let’s have a look at ring-2. For ring-2, direction of magnetic field is perpendicular to the plane of paper/sheet, and directed outwards. In the same way as ring-1, the decreasing current will now make the upper face of the ring the north-pole after electromagnetic induction.
Thus this is implying that the direction of induced current will be anti-clockwise in ring-2.

Note: In electromagnetic induction, if the magnetic field direction is moving away from a target area, then according to Lenz’s law, magnetic flux linked with the area decreases, inducing a south-pole and vice-versa. Keep in mind that you are using the right hand thumb rule for predicting the direction of the magnetic field. Also, go through Fleming’s left and right hand rules, problems with their applications are common in several entrances.