What is the working principle of a DC motor? --- Sireesha, Tirupathi, India
Marshall Brain Answers:
The working principle behind any DC motor is the attraction and repulsion of magnets. The simplest motors use electromagnets on a shaft, with permanent magnets in the case of the motor that attract and repel the electromagnets. The reason for using electromagnets is so that it is possible to flip their magnetic field (their north and south poles).
So the electromagnet is attracted to one of the permanent magnets. As soon as it reaches the permanent magnet, it's north and south poles flip so that it is repelled from that magnet and attracted to the other permanent magnet. This video shows you the parts and how they fit together:
It is possible to get even simpler, although at that point the motor changes from being useful to merely instructive, as shown here:
The key to this demonstration motor is the fact that the insulation coating on the wire ends is only removed from one side of one of the wires, as illustrated on this page.
See also: How Electric Motors Work