Answer:
Electric MotorIt is a
rotating device which convertselectrical energy into mechanical energy.
Principle
Electric motor works on the
principle that when acurrent-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. (1)
The diagram of electric motor
is shown below
(1)
Working
(i) 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 brush Q, via ring R2.
(ii) Applying Fleming's left
hand rule,
? No force acts on arm CB and DA
(as they are parallel to the magneticfield).
? Arm AB will experience a force
inupward direction.
? Arm CD will experience an
equal force in down ward direction.
? A torque, thus acts on the
coiland 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
thecurrent stops flowing. But the coil doesnot stop rotating due to inertia of motion.
(iv) When the coil passes the
vertical position, the ring automatically change their position and come 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 down ward
direction, Hence, the coil continues to rotate in anti-clockwise direction.
(2)
The split ring in an electric
motor acts as commentator, it reverses the direction of current flowing through
the armature coil (after every half rotation) (1)
Or
Electric Generator or Dynamo It
is a device which converts mechanical energy into electrical energy.
Principle
It works on the principle of the
electromagnetic induction, i.e., when there isa relative change in magnetic
field linked with a coil, there is an induced current in the coil. (1)
Electric generators are of two
types i.e.,
DC generators and AC generators (Alternators).
The diagram of electric
generator is shown below
Working
As the coil rotates, the two
rings also rotate with the coil. The brushes B1 and B2
always keep contact with therotating ring.
When the coil starts rotating
with the arm AB moving up and CD moving down (clockwise) cutting the
magneticlines then, according to Fleming's right hand rule, a current is
induced in these arms in the direction ABCD.
After a half rotation, arm CD
moves up and AB moves down, hence the direction of current in each segment changes,
giving rise to net induced current in the direction DCBA. Thus, after every
rotation, polarity of the currentin the respective arm changes thereby
generating an alternating current. (2)
The function of brushes (carbon-brushes)
is to make contact with the rotating rings of the commentator.
(1)
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