In order to increase the sensitivity of a moving coil galvanometer, one should decrease

Options

A. the strength of its magnet
B. the torsional constant of its suspension
C. the number of turns in its coil
D. the area of its coil

Answer

To solve the question regarding how to increase the sensitivity of a moving coil galvanometer, we need to analyze the factors that affect its sensitivity. The sensitivity (S) of a moving coil galvanometer is given by the formula:

\[ S = \frac{\theta}{I} = \frac{n \cdot B \cdot A}{C} \]

Where:
- \( S \) = Sensitivity
- \( \theta \) = Angular deflection
- \( I \) = Current through the coil
- \( n \) = Number of turns of the coil
- \( B \) = Magnetic field strength
- \( A \) = Area of the coil
- \( C \) = Torsional constant of the suspension

### Step-by-Step Solution:

1. **Understanding Sensitivity**: The sensitivity of the galvanometer is the ratio of the angular deflection to the current passing through the coil. Higher sensitivity means a larger deflection for a given current.

2. **Analyzing the Formula**: From the formula \( S = \frac{n \cdot B \cdot A}{C} \), we can see that sensitivity is directly proportional to the number of turns (n), magnetic field strength (B), and area of the coil (A), while it is inversely proportional to the torsional constant (C).

3. **Increasing Sensitivity**: To increase the sensitivity, we can:
- Increase \( n \) (number of turns)
- Increase \( B \) (magnetic field strength)
- Increase \( A \) (area of the coil)
- Decrease \( C \) (torsional constant)

4. **Identifying the Correct Option**: The question asks which factor should be decreased to increase sensitivity. Since sensitivity is inversely proportional to the torsional constant \( C \), we conclude that to increase sensitivity, we should decrease the torsional constant.

5. **Final Answer**: Therefore, the correct answer is that to increase the sensitivity of a moving coil galvanometer, one should decrease the torsional constant of its suspension \( C \).