A simple d.c. electric motor is fitted with a coil that rotates in a magnetic field. A commutator connects the power supply to the coil. What is the purpose of the commutator?
It converts a.c. into d.c. in the coil.
It prevents the current from becoming too great, because the coil has a low resistance.
It reverses the direction of the current in the coil after every 180° rotation of the coil.
It switches the current off momentarily after every 90° rotation of the coil.
