An electric motor is a device which converts electrical energy into mechanical energy.
Principle of electric motor: An electric motor essentially consists of a rectangular coil ABCD. Let the coil be connected to a battery cell B. Imagine the plane of the coil to be in plane of the paper.
With the help of Ampere's Right hand rule we imagine that the magnetic lines of force in all the four arms AB, BC, CD and AD will be directed perpendicular and into the plane of the paper. This makes the front face of the coil a south pole and the back face a north pole. Rectangular coil behaves as a magnet.
When such a current carrying coil is placed in an external fixed magnetic field it will be subjected to magnetic force according to Fleming's left hand rule.
The force rotates the coil imparting it a kinetic energy. If by some arrangement the coil is made to rotate continuously, electrical energy is converted to mechanical energy. Such an arrangement is called an electric motor.