Electric motor

Electric motor

Electric motor, any of a class of devices that convert electrical energy to mechanical energy, usually by employing electromagnetic phenomena.  Most electric motors develop their mechanical torque by the interaction of conductors carrying current in a direction at right angles to a magnetic field. The various types of electric motor differ in the ways in which the conductors and the field are arranged and also in the control that can be exercised over mechanical output torque, speed, and position.

Principle of operation

The basic principle on which motors operate is Ampere’s law. This law states that a wire carrying an electric current produces a magnetic field around itself. Imagine that current is flowing through The presence of that current creates a magnetic field around the wire. Since the loop itself has become a magnet, one side of it will be attracted to the north (N) pole of the surrounding magnet and the other side will be attracted to the south (S) pole of the magnet. The loop will begin to rotate.

AC motors. What happens next depends on the kind of electric current used to run the motor, direct (DC) or alternating (AC) current. With AC current, the direction in which the current flows changes back and forth rapidly and at a regular rate.

In the United States, the rate of change is 60 times per second, or 60 hertz (the unit of frequency).

In an AC motor, then, the current flows first in one direction through the wire loop and then reverses itself about 1/60 second later. This change of direction means that the magnetic field produced around the loop also changes once every 1/60 second. At one instant, one part of the loop is attracted by the north pole of the magnet, and at the next instant, it is attracted by the south pole of the magnet.

But this shifting of the magnetic field is necessary to keep the motor operating. When the current is flowing in one direction, the right hand side of the coil might become the south pole of the loop magnet. It would be repelled by the south pole of the outside magnet and attracted by the north pole of the outside magnet. The wire loop would be twisted around until the right side of the loop had completed half a revolution and was next to the north pole of the outside magnet.

If nothing further happened, the loop would come to a stop, since two opposite magnetic poles—one from the outside magnet and one from the wire loop—would be adjacent to (located next to) each other. And unlike magnetic poles attract each other. But something further does happen. The current changes direction, and so does the magnetic field around the wire loop. The side of the loop that was previously attracted to the north pole is now attracted to the south pole, and vice versa. Therefore, the loop receives another “kick,” twisting it around on its axis in response to the new forces of magnetic attraction and repulsion.

Thus, as long as the current continues to change direction, the wire loop is forced to spin around on its axis. This spinning motion can be used to operate any one of the electrical appliances mentioned above.

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