How to Convert a Galvanometer into a Voltmeter: A Comprehensive Guide

A galvanometer is an instrument that measures electric current in a circuit. While it does not measure voltage directly, it can be used to measure voltage indirectly with the right setup and use of Ohm's Law. This guide explains how to convert a galvanometer into a voltmeter and provides step-by-step instructions for practical applications.

Understanding Galvanometers and Voltage Measurement

Galvanometers function by detecting and indicating the presence of electric current in a circuit. They are highly sensitive and measure very low current levels. For voltage measurement, a galvanometer can be combined with a known resistance, allowing it to indirectly measure voltage using Ohm's Law. This method is particularly useful when precise voltage measurements are required, but a traditional voltmeter is not available.

How to Measure Voltage with a Galvanometer

Use Ohm's Law to Measure Voltage

By measuring the current flowing through the galvanometer and applying Ohm's Law, it is possible to determine the voltage across a resistor. The formula for Ohm's Law is:

V I × R

where V is voltage, I is the current measured by the galvanometer, and R is the resistance in series with the galvanometer. This method provides a practical way to measure voltage using a galvanometer and a known resistance.

Calibration for Accurate Voltage Measurements

To use a galvanometer for voltage measurement, it is important to ensure that it is calibrated for this purpose. One way to calibrate a galvanometer is to connect it across a known resistor and read the voltage based on the current deflection. This process involves measuring the current and applying Ohm's Law to calculate the voltage accurately.

Practical Examples: Building a Voltmeter

Using a Known Resistance to Build a Voltmeter

Suppose you have a galvanometer that gives full scale reading when 20 milliamp (mA) current passes through it, and you wish to build a voltmeter with a maximum voltage of 100 volts (V) corresponding to 100 deflection. To achieve this, you can add a series resistor to the galvanometer:

First, determine the required resistance R. Using the formula R V / I, where V is 100V and I is 20 mA (0.020A): R 100 V / 0.020 A 5000 ohms or 5K ohms. Select a galvanometer that is highly sensitive, giving full deflection for the smallest current, to ensure better accuracy.

This setup ensures that the galvanometer measures voltage accurately when used in conjunction with a known resistance.

Conclusion

Although a galvanometer primarily measures current, it can be effectively used for voltage measurement through a careful integration with a known resistance and the application of Ohm's Law. For direct and precise voltage measurements, professional voltmeters are typically used. However, understanding how to convert a galvanometer into a voltmeter offers valuable insights for practical and educational purposes.