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Moving coil galvanometer
Intermediate
Deflection is proportional to current.
The coil in a radial field feels constant torque NIAB, balanced by a spring κθ, so deflection ∝ I. Current sensitivity = NAB/κ.
Radial field keeps the scale linear.
Damping avoids overshoot.
In more detail
A moving-coil galvanometer uses a coil suspended in a magnetic field. The torque on the coil deflects a pointer, and a spring provides the restoring torque, so deflection is proportional to current.
Real-world uses
- Analogue ammeters and voltmeters use moving coils.
- Early instruments used galvanometers to measure small currents.
- Early ammeters used a moving-coil galvanometer, where the needle deflection shows the current through the coil.
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Frequently asked questions
Why is the deflection proportional to current?
The magnetic torque is proportional to current, and the spring torque is proportional to angle, so the two balance at a set angle.
How do I increase sensitivity?
Use more turns, a stronger field, or a weaker spring.
Why is the deflection proportional to current?
The magnetic torque is proportional to current, and a spring balances it, so the angle of deflection is proportional to the current.
Related topics in Magnetism & Induction
Force between parallel wires · Definition of the ampere · Torque on a current loop · Electric motor · Biot–Savart law · Field of a long straight wire