The National MagLab is funded by the National Science Foundation and the State of Florida.

# Galvanometer

A galvanometer detects and measures small amounts of current in an electrical circuit.

The first galvanometer was assembled by German mathematician and physicist Johann Schweigger, who called it a multiplier.

A galvanometer consists of a coil mounted so that it’s allowed to pivot freely within a magnetic field created by the poles of one or more permanent magnets. A needle is attached to the coil.

When electricity is allowed to pass through the coil, the magnetic field generated by the current-carrying wire interacts with the field of the permanent magnets, generating torque that rotates the coil. The deflection of the galvanometer’s needle is proportional to the current flowing through the coil. Here, we show you the concept of those interacting magnetic fields.

## Instructions

1. See the simple circuit set up between the battery and the coil.
2. Note how the coil is mounted between two permanent magnets, with opposite poles facing the coil.
3. Click the power button to close the knife switch and send an electric current to the coil. Notice what happens. The magnetic field generated by the current in the coil is at a right angle to the plane of the coil. This magnetic field causes the coil to swing, as the south pole of the coil's magnetic field is attracted to the north pole of the bar magnet field.
4. Click the flip battery button to reverse the direction of current through the coil. This reverses the poles of the magnetic field around the coil, so the coil swings in the opposite direction.
5. To stop the flow of electricity through the coil, click the off button.