Electric motor is a device used to convert electrical energy into mechanical energy.
Its working principle is that when a current carrying conductors is placed in magnetic feild , it experiences force.
The direction of force on this current carrying conductor can be determined by using Fleming's Left Hand Rule.
Feming's Left Hand Rule:
The objective of this rule is to determine the direction of force, on a current carrying conductor, when it is kept inside the magnetic field. If forefinger, middle finger and thumb are stretched perpendicular to each other such that forefinger points in the direction of applied magnetic field and middle finger points in the direction of electric current then thumb will point in the direction of force on a conductor.
An electric motor consists of a rectangular coil of many turns. This coil is called armature. It is fixed about an axis which is parallel to pendicular to its axis of rotation.
Ends of the coil are connected to two semi circular split rings. This ring is called commutator. A battery is connected to two carbon brushes to provide contact with each part of the commutator separately. When current passes through armature, forces act on its opposite sides in opposite direction. These forces make a couple of forces (torque) which rotate the armature about the fixed axis.
During rotation both parts of the commutator remain in contact with the carbon brushes separately. After rotation of 180o, the positions of the commutator is interchanged which reverse the dirction of the current through the armature and so the torque acts in the same direction (clockwise or anti-clockwise direction) .
Any object or parts of a device attached to the axle of motor will rotate along with it.
Note: If you need to show the diagram of D.C. Motor in the examination, then the below is one of the easy diagram to draw.