The best method to increase the sensitivity of a moving coil galvanometer is to increase the

Options

A. radius of the coil
B. number of turns of the coil
C. strength of radial magnetic field
D. increasing the elasticity of suspension fibre

Answer

To solve the problem of how to increase the sensitivity of a moving coil galvanometer, we need to analyze the factors that affect its sensitivity. The sensitivity of a galvanometer is defined as the deflection (θ) produced per unit current (i) flowing through the coil.

### Step-by-Step Solution:

1. **Understanding Sensitivity**:
The sensitivity (S) of a moving coil galvanometer can be expressed as:
\[ S = \frac{\theta}{i} \]
where θ is the deflection angle and i is the current.

2. **Torque in the Galvanometer**:
The torque (τ) acting on the coil due to the current is given by:
\[ \tau = n \cdot i \cdot A \cdot B \]
where:
- n = number of turns of the coil
- A = area of the coil
- B = strength of the magnetic field

3. **Restoring Torque**:
The restoring torque (Cθ) is proportional to the deflection angle θ:
\[ C \cdot \theta \]
At equilibrium, the deflection torque equals the restoring torque:
\[ n \cdot i \cdot A \cdot B = C \cdot \theta \]

4. **Expressing Sensitivity**:
Rearranging the above equation gives:
\[ \theta = \frac{n \cdot i \cdot A \cdot B}{C} \]
Substituting this into the sensitivity equation:
\[ S = \frac{n \cdot A \cdot B}{C} \]

5. **Factors Affecting Sensitivity**:
From the expression for sensitivity, we can see that to increase the sensitivity (S), we can:
- Increase the number of turns (n)
- Increase the area of the coil (A), which can be achieved by increasing the radius of the coil
- Increase the strength of the magnetic field (B)
- Decrease the constant (C), which relates to the elasticity of the suspension fiber

6. **Conclusion**:
Therefore, the best methods to increase the sensitivity of a moving coil galvanometer include increasing the radius of the coil, the number of turns of the coil, and the strength of the radial magnetic field. Increasing the elasticity of the suspension fiber can also help, but it is less direct compared to the other factors.

### Final Answer:
The best method to increase the sensitivity of a moving coil galvanometer is to increase the **number of turns of the coil**, **radius of the coil**, or **strength of the radial magnetic field**.