Electromagnetic Induction Laws

1 Mark Questions

1. The electric current flowing in a wire in the direction from B to A Find out the direction of

the induced current in the metallic loop kept the wire as shown in the figure.

Α В [All India 2014]

Ans. According to Lenz's law, the direction of induced current will oppose the cause of its production. So, the current in loop will induce in such a way that it will support the current flowing in the wire i.e., in the same direction. So, the direction of current in the loop will be clockwise

2.Two spherical bobs, one metallic and the other of glass, of the same size are allowed to fall freely from the same height above the ground. Which of the two wduld reach earlier and why? [Delhi 2014]

Ans. The glass bob will reach earlier on ground as acceleration due to gravity is independent of mass of the falling bodies. Being insulator, no induced current is developed in it due to the earth's magnetic field.

3.A flexible wire of irregular shape, abed as shown in the figure, turns into a circular shape when placed in a region field which is directed normal to the plane of the loop away from the reader. Predict the direction of the induced current in the wire.[Foreign 2014]

Х х Х Х х Х х × х х Х × х х ×

Ans. The wire is expanding to from a circle, which means that force is acting outwards on each part of the wire because of the magnetic field (acting in the downwards direction). The direction of the induced current should be such that it will produce magnetic field in upward direction (towards the reader). Hence, the force on the wire will be towards inward direction, i.e. induced current is flowing in anti-clockwise direction in the loop from cbadc.

4.In the given figure, a bar magnet is quickly moved towards a conducting loop having a capacitor. Predict the polarity of the plates A and B of the capacitor[All India 2014 C;2010;Hots] S Ans.

Ç As, the magnet moves towards the coil, flux linked with the coil increases, hence according to the Lenz's law, it will oppose the change.

Here, the North pole is approaching the magnet, so the induced current in the face of loop viewed from left side will flow in such a way that it will behave like North pole, so South pole developed in loop when viewed from right hand side of the loop. The flow of induced current is clockwise, hence A acquires positive polarity and B negative. (1)

5.State Lenz's law. A metallic rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an emf induced at its ends? Justify your answer. [Delhi 2013] Ans. Lenz's law states that the induced emf of induced current is a circuit which always opposes the cause that produces it. Yes, emf will be induced in the rod as there is change in magnetic flux. When a metallic rod held horizontally along East-West direction, is allowed to fall freely under gravity i.e. fall from North to South, the intensity of magnetic lines of the earth's magnetic field changes through it, i.e. the magnetic flux changes and hence the induced emf in it

6.State the Faraday's law of electromagnetic induction. [Foreign 2009,2012] Ans.