Consider a moving coil galvanometer (MCG): A. The torsional constant… | JEE Main 2025 (23 Jan, Shift 1)

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Kirchhoff's Laws & Measuring Instruments

Consider a moving coil galvanometer (MCG):

A. The torsional constant in moving coil galvanometer has dimensions $\left[\mathrm{ML^2T^{-2}}\right]$ B. Increasing the current sensitivity may not necessarily increase the voltage sensitivity. C. If we increase number of turns $(\mathrm{N})$ to its double $(2\mathrm{N})$ , 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:

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Answer: (b)

A: $\tau = k\theta$ and $\theta$ is dimensionless, so $[k] = [\mathrm{ML^2T^{-2}}]$ . True.
B: $V_s = \frac{I_s}{R}$ ; raising $I_s$ by more turns also raises R, so $V_s$ may not rise. True.
C: $N \to 2N$ doubles both $I_s$ and R, so $V_s$ is unchanged. False.
D: an ammeter needs a small shunt, not a large one. False. E: $I_s = \frac{NAB}{k} \propto N$ , not inverse. False.
So the answer is (b) A, B only.

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