The conversion of a moving coil galvanometer into a voltmeter is done by

Options

A. introducing a resistance of large value in series
B. introducing a resistance of small value in parallel
C. introducing a resistance of large value in parallel
D. introducing a resistance of small value in series

Answer

To convert a moving coil galvanometer into a voltmeter, we follow these steps:

### Step-by-Step Solution

1. **Understanding the Function of a Galvanometer**:
- A galvanometer is an instrument used to detect and measure small electric currents. It is designed to measure current by being connected in series with the circuit.

2. **Need for Conversion**:
- To measure voltage (potential difference) instead of current, we need to connect the galvanometer in parallel with the section of the circuit where we want to measure the voltage.

3. **Impact of Connecting a Galvanometer in Parallel**:
- When a galvanometer is connected in parallel, it should draw a very small current to avoid affecting the circuit's operation. If too much current flows through the galvanometer, it can lead to inaccurate readings.

4. **Introducing Resistance**:
- To limit the current through the galvanometer while still allowing it to measure voltage, we need to introduce a resistance. This resistance must be large enough to ensure that the majority of the current flows through the external circuit rather than the galvanometer.

5. **Connecting a Large Resistance in Series**:
- By connecting a large resistance (denoted as R) in series with the galvanometer (with resistance Rg), we can ensure that the current through the galvanometer remains small. The total voltage across the galvanometer and the series resistance can be expressed as:
\[ V = I_g \times (R + R_g) \]
- Here, \(I_g\) is the current through the galvanometer, \(R_g\) is the resistance of the galvanometer, and \(V\) is the voltage to be measured.

6. **Calculating the Required Resistance**:
- To find the value of the large resistance required, we can rearrange the equation:
\[ R = \frac{V}{I_g} - R_g \]
- This equation shows how to calculate the resistance needed to convert the galvanometer into a voltmeter.

7. **Conclusion**:
- Therefore, the correct method to convert a moving coil galvanometer into a voltmeter is to introduce a large resistance in series with it.

### Final Answer:
- The conversion of a moving coil galvanometer into a voltmeter is done by **introducing a resistance of large value in series**.