The working of dc motor depends upon the principle that when a current –carrying conductor is kept in a magnetic field, a force acts on the conductor which tends to rotate it. How this force acts and produces a continuous motion is explained below:
Also Read: Working Principle of DC Generator
A sectional view of a loop of wire is shown under north and south poles. The current in conductor A shown inward while in conductor B it is outward. A force will act on both conductors A and B which will tend to rotate the loop in the anticlockwise direction. This direction of force is given by the Fleming’s left hand rule. This force will act till the conductors are in the magnetic field. Therefore, to obtain a continuous motion, many conductors are placed such that if one leaves the magnetic field, another enters it.When loop AB starts rotating, after a very short time, conductor B will come under the north pole and conductor A under the south pole. Now the current in conductor B is inward, while in conductor A it is outward as it is automatically changed with the help of the commutator. Again an anticlockwise force will act on the loop of wire and thus a continuous rotation is the anticlockwise direction will be obtained in this case.