c) a permanent magnet to rotate the armature
In an electric motor, a rectangular coil is placed in between the magnetic field and when current flows through the coil from the commutator rings, a torque acts on the coil which rotates it continuously. When the coil rotates, the shaft attached to it also rotates and thus mechanical work is done
- . In commercial electric motors field coils are used for producing magnetic fields and not a permanent magnet.
- These coils become magnetized when current is passed through them.
- Field coils give a stronger, more easily shaped magnetic field than permanent magnets.
- More the number of turns in the field coil, more the magnetic field.
- Therefore, the suitable field coil sizes are used for various commercial purposes.