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How Does an Electric Motor Work?

Time: 2010-12-24 11:02:43

DC-MotorAn electric motor uses electrical energy to produce movement, or mechanical energy. In doing this, it is basically the opposite end of the turbine that likely produced the electricity in the first place, converting the movement of a turbine blade into an electric charge. Since the invention of the first practical commercial electric motor in 1873, these devices have become essential and virtually ubiquitous tools that make electricity useful for doing work.


The operative principal in an electric motor is the same as an electromagnet. Known as Ampere's law, it states that an electric charge passing through a looped circuit produces a magnetic field. Inside an electric motor, in fact, is a basic electromagnet consisting of a wire circuit through which electricity flows. The result, as with any magnet, is an area of positive polarity and an opposite field of negative polarity.
Motion is produced by the attractive and repulsive force associated with the poles of magnets. In an electric motor it is the interaction of the internal electromagnet with a surrounding fixed magnet. The attraction and repulsion of the poles on the two magnets causes the electromagnet to begin rotating so as to align the opposite poles in the magnetic field. As it rotates, the electromagnet spins an axle, or armature, that performs the work of the electric motor. If that was all that happened, however, the poles would quickly align and the motor would stop. For the rotation to continue, the polarity of the electromagnet must reverse or flip, and the way this is achieved is what distinguishes the two main types of electric motors.


Electric motors fall into two types, depending on the input source of electricity, which will determine how the polarity is flipped. Most electric motors run on AC, or alternating current. Alternating current already by design changes the direction of its flow many times a second. In the electromagnet, the result is that the areas of positive and negative polarity rapidly reverse and alternate. This prevents the field from simply lining up and keeps the axle spinning. Any moving appliance such as a fan that is plugged into a wall outlet is powered by an AC electric motor.
Before AC current was invented by Nikola Tesla, however, motors operating on direct current, usually drawing their energy from a battery. The starter mechanism in an automobile is a modern example of a DC electric motor. In order to reverse the polarity and keep the axle spinning, the DC electric motor has an additional part called a commutator that alternates the direction of current into the electromagnet. This creates a sort of artificial alternation of the current, resulting change the direction of the flow of the electric charge and the necessary reversal of polarity. DC electric motors are somewhat more primitive than AC motors, but are useful in applications where AC current is not available.

 

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