Short Answer

A moving coil galvanometer is a device used to detect and measure very small electric currents. It works on the principle that a current-carrying coil placed in a magnetic field experiences a turning force. This force causes the coil to rotate, and the pointer attached to it shows the amount of current.

The moving coil galvanometer is very sensitive and is commonly used in laboratories and electrical instruments. Because it can measure tiny currents accurately, it forms the basis of many measuring devices such as ammeters and voltmeters.

Detailed Explanation

Moving coil galvanometer

A moving coil galvanometer is an instrument that measures small electric currents by using the interaction between electricity and magnetism. It is one of the most basic and important devices in electrical measurements. The device works on a simple but powerful principle: a current-carrying coil placed in a magnetic field experiences a torque (turning force). This torque causes the coil to rotate, and the rotation is shown through a pointer on a scale.

The device was developed by scientists such as Johann Schweigger and André-Marie Ampère, and later improved into a more sensitive and practical form. Today, the moving coil galvanometer is used in laboratories, experiments, and in the construction of various meters like ammeters, voltmeters, and ohmmeters.

Construction of a moving coil galvanometer

A moving coil galvanometer has the following main parts:

A rectangular coil made of thin copper wire
A strong permanent magnet shaped like a horseshoe
A soft iron core inside the coil
A light pointer attached to the coil
A spring that controls movement
A scale for readings

The coil is placed between the poles of the magnet, and the magnetic field is radial. This arrangement ensures that the torque acting on the coil is uniform and proportional to the current.

The coil is free to rotate and is connected to two springs that allow the current to pass through it. When no current flows, the coil stays at the zero mark. When current passes, the coil rotates, and the pointer shows the deflection.

Working of a moving coil galvanometer

The working is based on a simple principle:

A current-carrying conductor in a magnetic field experiences a force.

When current flows through the coil:

A magnetic force acts on both sides of the coil.
These forces create a turning effect (torque).
The coil begins to rotate.
The spring provides a restoring force to stop the coil from rotating too much.
The final position of the pointer depends on the balance between magnetic torque and spring force.

More current → more torque → larger pointer deflection.

Thus, the galvanometer gives a measure of the current strength.

Sensitivity of a galvanometer

A good moving coil galvanometer is highly sensitive, meaning it can detect even very small currents. Sensitivity increases when:

The number of turns in the coil is large
The magnetic field is strong
The coil is light
The restoring spring is soft

This sensitivity makes the device suitable for laboratory experiments requiring accurate measurements.

Uses of a moving coil galvanometer

A moving coil galvanometer has many uses in physics and electrical work:

Detecting small currents

It can sense extremely tiny currents that ordinary meters cannot measure.

Forming other electrical meters

By making small changes, a galvanometer can be converted into:

Ammeter (to measure current)
Voltmeter (to measure voltage)
Ohmmeter (to measure resistance)

Laboratory experiments

Students and scientists use galvanometers to study electric circuits, current flow, and electrical properties of materials.

Bridge and potentiometer circuits

Galvanometers act as null detectors in Wheatstone bridges and potentiometers.

Advantages of a moving coil galvanometer

Very sensitive
Accurate readings
Low power consumption
High efficiency
Scale is linear (equal divisions)

Limitations

Although useful, the galvanometer has some limitations:

It can only measure small currents
It cannot measure large currents directly
It is delicate and can be damaged by strong currents
It is affected by temperature changes

To protect the instrument, shunts or multipliers are used when converting it into other devices.

Difference between galvanometer and ammeter

A galvanometer is a sensitive instrument used only for detection and measurement of small currents. An ammeter, however, is designed to measure larger currents in circuits. Ammeter is created by adding a low-value shunt resistor to a galvanometer.

Conclusion

A moving coil galvanometer is a very important instrument in physics and electrical measurements. It works on the principle that a current-carrying coil in a magnetic field experiences a torque. This torque causes the coil to rotate, and the pointer shows the amount of current. The device is sensitive, accurate, and widely used in laboratories and for building other instruments like ammeters and voltmeters. It remains an essential tool for understanding and measuring electric currents.