What is an electric motor? State it's principle.

State two ways by which the speed of rotation of an electric motor can be increased.

A copper wire is held between the poles of a magnet. There is a switch provided to reverse the current in the wire. Also, the polarity can be changed. In how many directions can the force act on the wire?

A flat coil ABCD is freely suspended between the pole pieces of a U-shaped permanent magnet with the plane of coil parallel to the magnetic field.

(a) What happens when a current is passed in the coil?

(b) When will the coil come to rest?

(c) When will the couple acting on the coil be (i) maximum, (ii) minimum?

(d) Name an instrument which makes use of the principle stated above.