1. Action of current on magnet: A current-carrying conductor produces a magnetic field around it. So if a magnet is placed in that field it experiences a torque.
2. Action of magnet on current: If a current-carrying conductor is placed in a magnetic field, it experiences a force and hence if a current-carrying loop or coil is placed in a magnetic field, it experiences a torque.
3. Moving magnet type Galvanometer: In such galvanometer is a freely suspended or pivoted magnet, due to the torque on it, it rotates in the magnetic field produced by current through a fixed conductor or coil.
Example: Tangent Galvanometer, Sine Galvanometer
4. Moving coil type Galvanometer: In this type of galvanometer is a freely suspended coil, due to the torque on it, it rotates in the magnetic field produced by a fixed permanent magnet.
Example: D’ Arsonval Galvanometer