Moving Coil galvanometer

A moving coil galvanometer is a key instrument for measuring and detecting small electric currents in physics experiments, working by translating electric current into pointer deflection through magnetic forces .

Construction

A moving coil galvanometer typically features a lightweight rectangular coil of copper wire, suspended between the poles of a strong horseshoe magnet . The coil’s plane is kept parallel to radial magnetic field lines using concave pole pieces, ensuring accurate and linear readings. Inside the coil, a soft iron core intensifies the magnetic field, while a spring or fine wire provides both support and a restoring force .

Working Principle

Current flowing through the coil creates a magnetic torque, turning the coil. The pointer attached to the coil moves over a scale, and the restoring force from the suspension wire keeps the system balanced. The deflection θ obeys:

$$=k\theta$$

where $N$ is number of turns, $B$ is field strength, $I$ is current, $A$ is coil area, and $k$ is torsional constant . Since deflection is proportional to current, the instrument is both sensitive and reliable.

Applications

• Measuring and detecting low currents in circuits

• Used in modified forms as ammeters (with low resistance shunt) and voltmeters (with high resistance in series)