Answer:
Electric
Motor
It is a rotating device which converts electrical energy into mechanical
energy.
Principle
Electric motor works on the principle that when a current-carrying
coil is placed in a magnetic field, two equal and opposite forces act upon it.
When these two forces (whose lines of action are not same) act on a body, it tends
to rotate, 
The diagram of electric motor is shown below
The function of commentator is to reverse, the direction
of current flowing through the coil every time the coil passes through the
vertical position i.e., after every half rotation.
The function of carbon brushses is to make contact with
the rotating rings of the commutator.
Working
Let coil ABCD be in horizontal position. When the key is
switched on the current flows in the direction DCBA and then leaves through the
brushes Q, via ring 
.
(ii) Applying Fleming's left-hand rule,
·
No force acts on arm CB and DA (as they are parallel to the
magnetic field).
·
Arm AB will experience a force in upward direction.
·
Arm CD will experience an equal force in downward direction.
·
A torque, thus acts on the coil and it rotates in anti-clockwise
direction.
(iii) While rotating, when the coil reaches the vertical
position, brushes P and Q lose contact
with rings and the current stops flowing. But the coil
does not stop rotating due to inertia of motion.
(iv) When the coil passes the vertical position, the ring
automatically change their position and came in contact with opposite brushes.
This reverses the direction of the current through the coil, but the direction
of current on right-hand side will be the same.
So, the force on right hand side is always upward and
force on left hand side of the coil is always in downward direction. Hence, the
coil continues to rotate anti-clockwise direction. The split rings in an
electric motor acts as commutator, it reverses the direction of current flowing
through the armature coil
(2)
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