The current sensitivity of a galvanometer can be increased by:
(A) decreasing the number of turns
(B) increasing the magnetic field
(C) decreasing the area of the coil
(D) decreasing the torsional constant of the spring
Choose the most appropriate answer from the options given below:

We need to identify which factors increase the current sensitivity of a galvanometer.

Current sensitivity is the deflection per unit current:

$$\frac{\theta}{I} = \frac{nBA}{k}$$

where $$n$$ = number of turns, $$B$$ = magnetic field, $$A$$ = area of coil, and $$k$$ = torsional constant of the spring.

(A) Decreasing the number of turns $$n$$ → Sensitivity decreases (since $$\frac{\theta}{I} \propto n$$). Incorrect.

(B) Increasing the magnetic field $$B$$ → Sensitivity increases (since $$\frac{\theta}{I} \propto B$$). Correct.

(C) Decreasing the area of the coil $$A$$ → Sensitivity decreases (since $$\frac{\theta}{I} \propto A$$). Incorrect.

(D) Decreasing the torsional constant $$k$$ → Sensitivity increases (since $$\frac{\theta}{I} \propto \frac{1}{k}$$). Correct.

The correct combination is (B) and (D).

Hence, the correct answer is Option D: (B) and (D) only.