Question

Current is induced in a coil by electromagnetic induction when:
A. Only the coil moves in the magnetic field
B. Only the magnet moves towards the coil
C. Coil and the magnet move with respect to each other
D. None of the above

Answer 1

Hint: We know from the Oersted’s experiment that the current and magnetism that is, the magnetic flux are directly related to each other. Current can be produced from magnetic fields and magnetic flux can be produced from current. A relative motion is needed to produce a change in magnetic flux between the magnet and the coil.

Complete answer:
Faraday’s Law of Electromagnetic Induction: According to the law, when the magnet is moved towards the coil, the needle of the Galvanometer, which is actually a very sensitive ammeter, will deflect away from its centre position in one direction only. When the magnet stops moving and is held stationary with reference to the coil, then the needle of the galvanometer returns back to zero as there is no physical movement of the magnetic field.
Similarly, when the magnet is moved away from the coil within the opposite direction, the needle of the galvanometer deflects within the opposite way with regards to the first indicating a change in polarity. Then by moving the magnet back and forth towards the coil the needle of the galvanometer will deflect left or right, positive or negative, relative to the directional motion of the magnet.
If the magnet is now held stationary and the coil is moved towards or away from the magnet, then the needle of the galvanometer will also deflect in either direction depending upon where it is moving. Then the action of moving a coil or loop of wire through a magnetic flux induces a current.
So the Faraday’s states that there must be a “relative motion” or movement between the coil and the magnet to generate electric current in the coil.

Hence option C is the correct one.

Note: If both the coil and the magnet move with the same speed and in the same direction, the relative motion would be zero and no current will be produced in the coil and there won’t be a deflection in the galvanometer. The relative motion between current and the coil has to be either positive or negative, but it cannot be zero.