I've not understand how a dc motor works. please someone help me to understand it?

Question

abt the current and if you could explian to me in detail how its diffrent witn an ac motor

Answer 1

A DC motor is a very basic type of motor. It will use permanent magnets, an armature and a commutator ring to control its function.
The armature is an electro-magnet that can be switched on and off. The commutator ring is the switching mechanism.
As you know, unlike poles if two magnets attract each other and like poles repel.
The commutator ring has electric (DC) power applied to it. It is connected (both mechanically and electrically) to the electromagnetic coils of the armature.
The armature creates a magnetic field and is drawn toward the permanent magnets arranged around the outside circumference of the armature. Of course the opposite pole of the electromagnet is repelled by the opposite ends of the permanent magnets.
Obviously, once the magnets react their point of greatest attraction, all motion will stop.
Before the rotating armature reaches that point, the magnetic field induced in the electromagnets is reversed by switching the direction of the current flowing through the armature's coils.. That switching is accomplished at the commutator ring, which is mechanically attached to the armature.
The cycle continues and you have a very basic motor.
There is no speed control with this type of motor. Speed is usualy limited by load.
With an AC motor the magnetic fields are reversed by the fact that the current is constantly reversing. There speed is controled by the frequency of the alternating current.
There are many more type of both AC and DC motors.
This is very basic. An extensive study of motor technology cannot be written in this format. It would fill volumes.