Correct Answer - Option 2 : Galvanometer

**Sensitivity Of Moving Coil Galvanometer:**

The general definition of the sensitivity experienced by a moving coil galvanometer is given as the ratio of change in deflection of the galvanometer to the change in current in the coil.

S = dθ/dI

The sensitivity of a galvanometer is higher if the instrument shows larger deflection for a small value of current. Sensitivity is of two types, namely current sensitivity and voltage sensitivity.

**Current Sensitivity:**

The deflection θ per unit current I is known as current sensitivity θ/I

θ/I = nAB/k

**Voltage Sensitivity:**

The deflection θ per unit voltage is known as Voltage sensitivity θ/V. Dividing both sides by V in the equation θ= (nAB / k)I;

θ/V= (nAB /V k)I = (nAB / k)(I/V) = (nAB /k)(1/R)

R stands for the effective resistance in the circuit.

Voltage sensitivity = Current sensitivity/ Resistance of the coil.

Therefore, under the condition that R remains constant;

**Voltage sensitivity ∝ Current sensitivity.**

**The figure of Merit of a Galvanometer: ****It is the ratio of the full-scale deflection current and the number of graduations on the scale of the instrument and is designed to be sensitive to extremely low current levels.**

It is also the reciprocal of the current sensitivity of a galvanometer.

**Factors Affecting Sensitivity Of A Galvanometer:**

- Number of turns in the coil
- Area of the coil
- Magnetic field strength B
- The magnitude of couple per unit twist k/nAB