Question

When galvanometer is converted into voltmeter?

Answer 1

To convert a galvanometer into a voltmeter, a high-value resistor, known as a shunt resistor, is added in series with the galvanometer. This allows the galvanometer to measure higher voltages than it could on its own. The resistance value of the shunt is calculated based on the desired voltage range and the sensitivity of the galvanometer. By doing this, the galvanometer can measure voltage directly while still protecting it from excessive current. Would you like to delve deeper into how the calculations are made?

Answer 2

A galvanometer is a sensitive instrument used to detect and measure small electric currents. When it is converted into a voltmeter, the goal is to measure the potential difference (voltage) across two points in a circuit. This conversion is done by incorporating a resistor in series with the galvanometer. Here’s a detailed breakdown of the process:

### Steps to Convert a Galvanometer into a Voltmeter

1. **Understanding the Galvanometer**:
   - A galvanometer typically has a full-scale deflection (FSD) current, denoted as \( I_g \), and an internal resistance \( R_g \). The galvanometer's needle deflects based on the current flowing through it.

2. **Choosing the Series Resistor**:
   - To convert the galvanometer into a voltmeter, a resistor \( R_s \) is added in series with the galvanometer. The value of this resistor needs to be calculated based on the desired voltage range of the voltmeter.

3. **Voltage Measurement**:
   - When voltage \( V \) is applied across the combination of the series resistor \( R_s \) and the galvanometer, the current through the circuit is \( I = \frac{V}{R_g + R_s} \). The galvanometer will show a deflection corresponding to this current.

4. **Calculating the Series Resistor**:
   - To ensure the galvanometer only registers the full-scale deflection at a specific voltage \( V \), you can use Ohm’s Law and the characteristics of the galvanometer:
     \[
     V = I_g \cdot (R_g + R_s)
     \]
   - Rearranging gives:
     \[
     R_s = \frac{V}{I_g} - R_g
     \]
   - This equation allows you to calculate the necessary resistance for your desired voltage measurement.

5. **Final Configuration**:
   - After adding the appropriate series resistor, the new device will behave like a voltmeter. The voltmeter will measure the voltage across its terminals when connected in parallel to the circuit whose voltage you wish to measure.

### Key Points

- **Range Limitation**: The maximum voltage that can be measured is limited by the full-scale deflection of the galvanometer and the value of the series resistor.
- **Calibration**: It is often necessary to calibrate the voltmeter to ensure accuracy, especially if multiple ranges are implemented using different series resistors.
- **Sensitivity**: The sensitivity of the voltmeter can be adjusted by selecting different values of \( R_s \), allowing for various voltage ranges.

### Conclusion

In summary, a galvanometer can be converted into a voltmeter by adding a suitable resistor in series. This allows for the measurement of voltage by ensuring that the current through the galvanometer does not exceed its rated capacity while enabling it to display the corresponding voltage across the series resistor and itself. This technique is fundamental in electrical measurements and is widely used in practical applications.