Question

A coil of insulated copper wire is connected to a galvanometer. What happens, if a bar magnet is:
i. Pushed into the coil?
ii. Withdrawn from inside the coil?
iii. Held stationary inside the coil?

Answer 1

Hint: The movement of bar magnet in the coil of insulated Copper wire connected to a galvanometer produces an induced electromotive force or better known as emf. This produced emf tends to repulse the reason for its creation only.

Complete step-by-step answer:
A Galvanometer is a device used to detect and indicate electric current. So it is clear that this question focuses on the Induction of current in a coil, where the coil which signifies an electric circuit is kept stationary and the bar magnet which signifies the magnetic field is in motion.
The phenomenon which works here is the Faraday’s Law of Induction, which is also known as Electromagnetic Induction. Also it is very crucial to note that for current to induce relative motion is mandatory between the coil and the magnet, here the coil is stationary so it is significant that the magnet is in motion to ensure current induction.
Based on this phenomenon, let us consider the three cases mentioned above-
i. Pushed into the coil- When the magnet is pushed into the coil, the pointer in the galvanometer gives current detection because current induction takes place in the coil due to electromagnetic induction which happened due to relative motion between magnetic field(bar magnet) and electric circuit(the coil).

ii. Withdrawn from inside the coil- The direction of motion of the magnet here is different from the first case but electromagnetic induction is taking place, so again the galvanometer shows the current detection but the pointer is directed in the opposite direction from the first case.

iii. Held Stationary inside the coil- Due to the coil and the magnet being stationary, there is no possibility of electromagnetic induction resulting in no current induction in the coil. So, the galvanometer will not show any deflection meaning current is not induced in the coil.

Additional Information:
i. A galvanometer is a device used to detect and indicate electric current using a deflecting pointer. It is an electromechanical device.
ii. Faraday’s Law of Induction is a law to predict the interaction of a magnetic field with an electric circuit to produce a difference in potential that tends to give rise to an electric current. This phenomenon is also known as electromagnetic induction.

Note: There is no current induction without any relative motion between the coil and the magnet, so if either the bar or the coil is moving current will be induced but if both are stationary no current induction will be produced.