# Theory and Operation of Moving Coil Ballistic Galvanometer

Ballistic Galvanometer is a type of galvanometer that measures the current or voltage in an alternating current circuit. It is also known as a moving coil meter or a moving coil ammeter.

## Ballistic Galvanometer Operation

Ballistic Galvanometer measures the current or voltage in an alternating current circuit by using a moving coil placed in a magnetic field. A magnetic field that opposes the magnetic field in the magnetic circuit is produced as the current passes over the coil. This opposition causes the coil to move and its speed depends on the current magnitude and frequency. The moving coil then strikes a spring balance to rotate the pointer of the meter and indicate the value of the current or voltage being measured.

## Theory of Ballistic Galvanometer

Ballistic Galvanometer Theory is based on Faraday’s Law of Electromagnetic Induction, which states that when a wire carrying a current is placed in a magnetic field, a force is exerted on the wire, causing it to move. This force works perpendicular to both the directions of the current and magnetic field and is proportional to the product of the current and magnetic field strength. The moving coil ballistic galvanometer uses this principle to measure current or voltage by placing a wire carrying the current or voltage in a magnetic field and measuring the force exerted on the wire.

## Theory of Moving Coil Ballistic Galvanometer

Theory of Moving Coil Ballistic Galvanometer can be divided into two parts:

1. Basic theory
2. Practical applications

### 1. Basic Theory

In moving coil ballistic galvanometer, the moving coil is placed in a magnetic field produced by either a permanent magnet or an electromagnet. The magnetic field exerts a force against the magnetic field’s direction on the moving coil. This force causes the coil to accelerate and move through the magnetic field. The speed of the moving coil depends on the magnitude and frequency of the current being measured and can be related to the velocity of the coil using Newton’s Second Law of Motion, which states that force equals mass times acceleration. The force acting on the moving coil can be expressed using Ampere’s Law, which states that the sum of the forces acting on a current-carrying wire equals the product of the current and the reluctance of the magnetic circuit.

### 2. Practical Applications

Moving Coil Ballistic Galvanometer can be used to measure ac currents up to about 100 A or ac voltages up to about 1000 V. The moving coil ballistic galvanometer measures current or voltage by placing a wire carrying the current or voltage in a magnetic field and measuring the force exerted on the wire. The moving coil then strikes a spring balance to rotate the pointer of the meter and indicate the value of the current or voltage being measured. The spring balance used in moving coil ballistic galvanometer meters is typically made of leaf springs or flexures, which provide high stiffness and low damping for accurate measurements. The spring balance is coupled to a pointer through a linkage mechanism that converts the small movements of the spring balance into large angular displacements of the pointer.