Question

How will you convert a moving coil galvanometer into an ammeter?

Hint:

A shunt resistor bypasses most of the current in a galvanometer, allowing the instrument to measure larger currents without being damaged.

Answer 1

Step 1: Understanding the galvanometer.
A moving coil galvanometer is designed to measure small currents. It has a limited current range, and applying a large current can damage the instrument. To measure larger currents, we need to modify the galvanometer.
Step 2: Adding a shunt resistor.
To convert the galvanometer into an ammeter, a shunt resistor \( R_{\text{shunt}} \) is connected in parallel with the galvanometer. The shunt resistor is chosen such that it allows most of the current to bypass the galvanometer, protecting it from high current values.
Step 3: Calculation of shunt resistance.
The value of the shunt resistor is calculated based on the full-scale current \( I_{\text{full}} \) the ammeter should measure and the full-scale deflection current \( I_{\text{g}} \) of the galvanometer. The shunt resistance is given by: \[ R_{\text{shunt}} = \frac{V_{\text{g}}}{I_{\text{full}}
- I_{\text{g}}} \] where \( V_{\text{g}} \) is the voltage across the galvanometer when it reads the full-scale current \( I_{\text{g}} \).
Step 4: Conclusion.
The addition of the shunt resistor effectively increases the range of the galvanometer, converting it into an ammeter that can measure large currents.