Question

What is the principle of a moving coil galvanometer? Draw its neat labelled diagram. How is the sensitivity of the galvanometer increased?

Hint:

To increase the sensitivity of a galvanometer, increase the number of turns in the coil, use a larger coil area, and use a stronger magnetic field. A lower spring constant also improves sensitivity.

Answer 1

Principle of a Moving Coil Galvanometer:
A moving coil galvanometer is an instrument used for detecting and measuring small electrical currents. It operates on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a force. This force is given by: \[ F = BIL, \] where:
- \( B \) is the magnetic field strength,
- \( I \) is the current passing through the conductor,
- \( L \) is the length of the conductor in the magnetic field.
In a moving coil galvanometer, a coil of wire is placed in a uniform magnetic field. When a current flows through the coil, it experiences a torque, causing the coil to rotate. The deflection of the coil is proportional to the current flowing through it. A spring is used to restore the coil to its original position, and a scale is used to measure the deflection. Increasing Sensitivity:
The sensitivity of a moving coil galvanometer depends on factors such as:
1. Number of turns in the coil: Increasing the number of turns in the coil increases the torque for a given current, which increases the sensitivity.
2. Area of the coil: Increasing the area of the coil also increases the torque, thus improving the sensitivity.
3. Strength of the magnetic field: A stronger magnetic field increases the force acting on the coil, thus increasing the sensitivity.
4. Spring constant: A lower spring constant makes the galvanometer more sensitive, as it requires less force to produce a given deflection.
By optimizing these factors, the sensitivity of the galvanometer can be increased, allowing it to measure smaller currents more accurately.