Question

In which direction, deflection in the galvanometer occurs?
$\text{A}\text{.}$ Towards right
$\text{B}\text{.}$ Towards Left
$\text{C}\text{.}$ No deflection
$\text{D}\text{.}$ None of these

Answer 1

Hint- Here, we will proceed by showing what happens when a bar magnet is placed in the proximity of a coil containing a galvanometer. Then, according to Lenz’s law, we will be determining the direction of the induced current.

Complete step-by-step solution -

When the magnet is held stationary, the galvanometer shows no deflection.
When the north pole of the magnet is brought towards the coil, the galvanometer shows a sudden deflection indicating that a current is induced in the coil.
The galvanometer deflection is temporary and it lasts as long as the bar magnet is in motion. There won't be any deflection when the bar magnet is held stationary anywhere.
When the magnet is moved away from the coil, the galvanometer shows deflection in the opposite direction indicating the direction of induced current in the reversed direction.
When the south pole of the bar magnet is moved towards or away from the coil, the deflection in the galvanometer will be opposite to that observed with the north pole for similar movements.
This indicates that when there is a relative motion between the coil and the magnet a current is induced in the coil. This current gets detected with the help of a galvanometer.
This experiment shows that a current flows in the coil only when there is a relative motion between the coil and the magnet due to which the galvanometer connected with the coil shows deflection. The direction of deflection in a galvanometer is reversed if the direction of motion (or polarity of the magnet) is reversed.
This indicates that whenever there is a change in the magnetic flux linked with a coil, an emf is induced. The induced emf lasts so long as there is a change in the magnetic flux linked with the coil. This phenomenon in which an electric current is induced in a conductor because of a changing magnetic field is called electromagnetic induction.
The magnitude of the induced emf is given by
$\text{e}=-{\displaystyle \frac{d\varphi }{dt}}$ where $\varphi$ denotes the magnetic flux
 By Lenz’s law, the direction of the induced current (induced due to induced emf) must be such that its own magnetic field is directed in a way to oppose the changing flux caused by the field of the approaching magnet.
The change in magnetic flux caused by the approaching magnet induces a current in the loop. (a) An approaching north pole induces a counter clockwise current with respect to the bar magnet.
(b) An approaching south pole induces a clockwise current with respect to the bar magnet.
As we know that when current flows from positive terminal to the negative terminal of the galvanometer, the pointer of the galvanometer deflects towards positive terminal and when current flows from negative terminal to the positive terminal of the galvanometer, the pointer of the galvanometer deflects towards negative terminal.
Here, when the south pole is brought near the coil, clockwise current flows in the circuit (i.e., from positive terminal of the galvanometer to the negative terminal), the deflection in the galvanometer occurs towards the left (or positive terminal).
Therefore, option B is correct.

Note- The galvanometer is the device used for detecting the presence of small current and voltage or for measuring their magnitude. The galvanometer is mainly used in the bridges and potentiometers where they indicate the null deflection or zero current. The deflection in the galvanometer will be larger when the magnet is pushed or pulled away from the coil faster.