Consider a moving coil galvanometer (MCG):
A. The torsional constant in moving coil galvanometer has dimensions $[ML^2T^{-2}]$.
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:
Answer: (D) A, B only
Current sensitivity $\dfrac{\theta}{I} = \dfrac{NAB}{k}$; voltage sensitivity $\dfrac{\theta}{V} = \dfrac{NAB}{kR_G}$.
- A: $\tau = k\theta$ with $\theta$ dimensionless, so $[k] = [\tau] = [ML^2T^{-2}]$. Correct.
- B: Raising $N$ raises the current sensitivity, but it also raises the coil resistance $R_G$, so the voltage sensitivity need not increase. Correct.
- C: Doubling $N$ doubles both $NAB$ and (roughly) $R_G$, so the voltage sensitivity stays about the same. Wrong.
- D: An ammeter needs a shunt of **small** resistance. Wrong.
- E: Current sensitivity is directly proportional to $N$. Wrong.
A, B only.
Solution by Sreeraj P, M.Sc Physics