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    An electric motor at home takes in AC power.  The Alternating current direction is changed at the half cycle of the time period of the supply current.

     An electric motor  converts electrical energy into mechanical (Rotational) energy.  It uses the principle of a electro-magnetic force exerted on a current carrying conductor (loop) coil, when it is placed inside a strong magnetic field.

    In side the motor, we have essentially the same parts as the generator.  We have a stator - which consists of two strong permanent magnets North and south poles in hollow cylindrical shape.  In between the magnets, there is a rotor.  It is in the shape of a cylindrical shaft.  Around it, in the shape of a rectangle (planar surface to planar surface) there are windings made of a good and thick conductor.  There is an air gap between the rotor and the stator.

    When current flows in the coil, the magnetic field exerts force on the coil, so the rotor rotates.  When the half cycle is reached ie., 1/2 rotation is complete, the direction of the current is changed if it is AC generator.  This is done by using what is called as a commutator (using slip rings).  If it is a DC generator, then the direction is in one direction. So there is no problem.

   The average speed of the motor is proportional to the emf.

The emf and rotational speed are related as:

Emf = Ф * Z * N  / 60 * (P / A) = k * ω

Ф = magnetic flux through a conductor
Z = number of armature conductors (turns)
N = rotations of the motor per minute. =  60 w/(2 pi)
ω = angular speed of the motor
P = number of poles
A = number of parallel paths in the armature.
     A = 2 for simplex wave winding of the motor/generator
     A = P  for simplex lap-wound motor /generator

k = proportionality constant.
If operating current I and internal (armature) resistance R are given, then
   Emf = voltage across motor = Input voltage V - I R

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