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An '''electric motor''' is a device which converts electrical energy into kinetic and mechanical energy. Most electric motors utilise the [[motor effect]] in the collective deflection of a flow of electrons through a wire to turn a coil, however other models employ more ingenious devices such as the induction of [[eddy currents]].
An '''electric motor''' is a device which converts electrical energy into kinetic and mechanical energy. Most electric motors utilise the [[motor effect]] in the collective deflection of a flow of electrons through a wire to turn a coil, however other models employ more ingenious devices such as the induction of [[eddy currents]].
==Basic Motors==
==Basic Motor Design==
A basic motor consists of a coil placed in a magnetic field. As current passes through the coil it will experience a force such that one side of the coil will be deflected upwards and the other side downwards (as the current is running in opposite directions), resulting in the coil turning. When the coil turns such that is is parallel to the magnetic field (and hence no force of deflection) the direction of the current is reversed, both sides of the coil will now experience a force in the opposite direction, resulting in the coil continuing to turn. As the current is reversed every 180<sup>O</sup> turn of the coil it will continue to turn provided there is a power input.
A basic motor consists of a coil placed in a magnetic field. As current passes through the coil it will experience a force such that one side of the coil will be deflected upwards and the other side downwards (as the current is running in opposite directions), resulting in the coil turning. When the coil turns such that is is parallel to the magnetic field (and hence no force of deflection) the direction of the current is reversed, both sides of the coil will now experience a force in the opposite direction, resulting in the coil continuing to turn. As the current is reversed every 180<sup>O</sup> turn of the coil it will continue to turn provided there is a power input.
An AC synchronous motor uses a slip ring commutator instead of a split ring commutator, in which a fixed circuit feeds power to the coil. The current is reversed in the coil as the current from the power source reverses direction. However, in order to keep the current in the coil travelling in the same direction with respect to the stator field (and hence keep the coil turning in the same direction) the motor needs to turn at the same frequency as the frequency of the current (eg in countries where alternating current operates at 50Hz the motor would have to turn exactly 50 times per second, or at 3000 rpm). Although this is a major drawback of AC synchronous motors it can be overcome using gears to allow larger objects to turn at a lesser speed.
An AC synchronous motor uses a slip ring commutator instead of a split ring commutator, in which a fixed circuit feeds power to the coil. The current is reversed in the coil as the current from the power source reverses direction. However, in order to keep the current in the coil travelling in the same direction with respect to the stator field (and hence keep the coil turning in the same direction) the motor needs to turn at the same frequency as the frequency of the current (eg in countries where alternating current operates at 50Hz the motor would have to turn exactly 50 times per second, or at 3000 rpm). Although this is a major drawback of AC synchronous motors it can be overcome using gears to allow larger objects to turn at a lesser speed.
==AC Induction Motor==
An AC induction motor indirectly uses the [[motor effect]], but it primarily relies on the induction of [[eddy currents]] and [[Lenz's Law]] to turn a motor. The motor consists of a squirrel cage ([http://users.deec.ist.utl.pt/~ineit/imdrives/glossaryimages/fig_squirrel_cage.gif picture here]) placed inside a ring of electromagnets. Half the electromagnets are connected such that their poles are south when the poles of the other half are north. An AC current is used to power the electromagnets so that their poles are constantly swapping. This results in a changing magnetic field with respect to the conducting bars of the cage, which [[Electromagnetic induction|induces]] a current such that its magnetic field interacts with the stator field to produce a force (motor effect) which opposes the relative motion between the two fields (Lenz's Law). As the electromagnets of the stator field are fixed in position the squirrel cage experiences the force and begins to turn to reduce the slip velocity (the relative motion between the cage and the stator field), as a result the limiting speed of an induction motor can reach is the frequency of the current. Because of their simplicity in design AC induction motors are in regularly use, and up to 95% of household appliances which use motors use AC induction motors.
==See Also==
==See Also==