JEE Main 2025 Jan 23 Shift 1, Physics Q10: Moving Coil Galvanometer

JEE Main2025Jan 23, Shift 1Physics

Consider a moving coil galvanometer (MCG) :

A : The torsional constant in moving coil galvanometer has dimensions $[M L^{2} T^{- 2}]$

B : Increasing the current sensitivity may not necessarily increase the voltage sensitivity.

C : If we increase number of turns (N) to its double (2N), then the voltage sensitivity doubles.

D : MCG can be converted into an ammeter by introducing a shunt resistance of large value in parallel with galvanometer.

E : Current sensitivity of MCG depends inversely on number of turns of coil.

Choose the correct answer from the options given below :

A
A, B only
B
A, D, only
C
B, D, E only
D
A, B, E only

Solution

For a galvanometer in equilibrium, $τ_{magnetic} = N I A B$ balances the restoring torque $C θ$ , giving $θ = \frac{N A B}{C} I$ .

(A) From $τ = C θ$ , $[C] = [τ] = [M L^{2} T^{- 2}]$ (since $θ$ is dimensionless). True.

(B) Current sensitivity $\frac{θ}{I} = \frac{N A B}{C}$ . Voltage sensitivity $\frac{θ}{V} = \frac{N A B}{C R}$ . Increasing $N$ also increases $R$ (longer wire), so voltage sensitivity may not increase. True.

(C) Voltage sensitivity $\propto \frac{N}{R}$ . Doubling $N$ roughly doubles $R$ as well, so the ratio stays the same. False.

(D) Ammeter requires a small shunt in parallel (not large). False.

(E) Current sensitivity $\frac{N A B}{C}$ is proportional to $N$ , not inversely related. False.

$∴$ A and B only.

Concept behind this question

Moving Coil GalvanometerNotes, formulas and examples →

Practice more Physics

Concept-wise practice with instant solutions on Fundamenthol.

Start practicing →

JEE Main 2025 Jan 23 Shift 1, Physics Q10: Moving Coil Galvanometer

Concept behind this question

More previous year questions on Moving Coil Galvanometer

Practice more Physics