The document discusses the components and operation of an electric motor. It describes how an electric motor uses magnetic fields and electromagnetic induction to convert electrical energy into mechanical energy and create rotational motion. The key components of an electric motor are an armature or rotor that acts as an electromagnet, field magnets, a commutator, and brushes. When current is passed through the armature windings, it interacts with the magnetic field of the stationary field magnets, causing the armature to rotate. The commutator and brushes work together to switch the direction of current in the armature coils at the right moment to maintain rotation.
1. Electric MotorElectric Motor
By Kapil AgarwalBy Kapil Agarwal
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2. Magnetic Force On A Current –Magnetic Force On A Current –
Carrying ConductorCarrying Conductor
The magnetic force (F) the conductorThe magnetic force (F) the conductor
experiences is equal to the product of itsexperiences is equal to the product of its
length (L) within the field, the current I inlength (L) within the field, the current I in
the conductor, the external magnetic fieldthe conductor, the external magnetic field
B and the sine of the angle between theB and the sine of the angle between the
conductor and the magnetic field. In shortconductor and the magnetic field. In short
F= BIL (sinF= BIL (sinθθ))
3. The force on a current-carryingThe force on a current-carrying
conductor in a magnetic fieldconductor in a magnetic field::
When a current-carrying conductor is placed in aWhen a current-carrying conductor is placed in a
magnetic field, there is an interaction between themagnetic field, there is an interaction between the
magnetic field produced by the current and themagnetic field produced by the current and the
permanent field, which leads to apermanent field, which leads to a forceforce beingbeing
experienced by the conductor:experienced by the conductor:
4. The magnitude of the force on the conductor dependsThe magnitude of the force on the conductor depends
on the magnitude of the current which it carries. Theon the magnitude of the current which it carries. The
force is a maximum when the current flowsforce is a maximum when the current flows
perpendicularperpendicular to the field (as shown in diagram A onto the field (as shown in diagram A on
the left below), and it is zero when it flowsthe left below), and it is zero when it flows parallelparallel toto
the field (as in diagram B, on the right):the field (as in diagram B, on the right):
6. The directional relationshipThe directional relationship
of I in the conductor, theof I in the conductor, the
external magnetic field andexternal magnetic field and
the force the conductorthe force the conductor
experiencesexperiences
I
F
B
7. Motion of a current-carrying loop in aMotion of a current-carrying loop in a
magnetic fieldmagnetic field
N S
L R
I
F
F Rotation
Commutator
(rotates with
coil)
brushes
9. Electric MotorElectric Motor
An electromagnet is the basis of anAn electromagnet is the basis of an
electric motorelectric motor
An electric motor is all about magnets andAn electric motor is all about magnets and
magnetism: A motor usesmagnetism: A motor uses magnetsmagnets toto
create motion.create motion.
Opposites attract and likes repel. Inside anOpposites attract and likes repel. Inside an
electric motor, these attracting andelectric motor, these attracting and
repelling forces createrepelling forces create rotational motionrotational motion..
A motor is consist of two magnets.A motor is consist of two magnets.
10. Parts of the MotorParts of the Motor
Armature or rotorArmature or rotor
CommutatorCommutator
BrushesBrushes
AxleAxle
Field magnetField magnet
DC power supply of some sortDC power supply of some sort
12. ArmatureArmature
The armature is anThe armature is an
electromagnet made byelectromagnet made by
coiling thin wire aroundcoiling thin wire around
two or more poles of atwo or more poles of a
metal core.metal core.
The armature has anThe armature has an axleaxle,,
and the commutator isand the commutator is
attached to the axle.attached to the axle.
When you run electricity intoWhen you run electricity into
this electromagnet, it createsthis electromagnet, it creates
a magnetic field in thea magnetic field in the
armature that attracts andarmature that attracts and
repels the magnets in therepels the magnets in the
stator. So the armature spinsstator. So the armature spins
through 180 degrees.through 180 degrees.
To keep it spinning, you haveTo keep it spinning, you have
to change the poles of theto change the poles of the
electromagnet.electromagnet.
13. Commutator and BrushesCommutator and Brushes
Commutator is simply a pair of platesCommutator is simply a pair of plates
attached to the axle. These plates provideattached to the axle. These plates provide
the two connections for the coil of thethe two connections for the coil of the
electromagnet.electromagnet.
Commutator and brushes work together toCommutator and brushes work together to
let current flow to the electromagnet, andlet current flow to the electromagnet, and
also to flip the direction that the electronsalso to flip the direction that the electrons
are flowing at just the right moment.are flowing at just the right moment.
14. The contacts of the commutator are attached toThe contacts of the commutator are attached to
the axle of the electromagnet, so they spin withthe axle of the electromagnet, so they spin with
the magnet. The brushes are just two pieces ofthe magnet. The brushes are just two pieces of
springy metal or carbon that make contact withspringy metal or carbon that make contact with
the contacts of the commutator.the contacts of the commutator.
18. A current-carrying coil in a magnetic field
experiences a turning effect.
How can the turning effect be increased?
A increase the number of turns on the coil
B reduce the size of the current
C reverse the direction of the magnetic field
D use thinner wire for the coil
19. What are the directions of the force in the leftWhat are the directions of the force in the left
and right loop?and right loop?
20. A student sets up the apparatus shown in
order to make a relay.
Which metal should be used to make the core?
A aluminium B copper
C ironD steel
