The Ammeter And The Voltmeter

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 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 the ammeter should measure and the full-scale deflection current of the galvanometer. The shunt resistance is given by: where is the voltage across the galvanometer when it reads the full-scale current .
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.