electric motor1

8/2/2019 Electric Motor1

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Electric Motor

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Magnetic Force On A CurrentCarrying Conductor

The magnetic force (F) the conductorexperiences is equal to the product of itslength (L) within the field, the current I in

the conductor, the external magnetic fieldB and the sine of the angle between theconductor and the magnetic field. In short

F= BIL (sin)


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The force on a current-carryingconductor in a magnetic field :

When a current-carrying conductor is placed in amagnetic field, there is an interaction between themagnetic field produced by the current and thepermanent field, which leads to a force beingexperienced by the conductor:


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The magnitude of the force on the conductor dependson the magnitude of the current which it carries. The

force is a maximum when the current flowsperpendicular to the field (as shown in diagram A onthe left below), and it is zero when it flows parallel tothe field (as in diagram B, on the right):


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Flemings left-hand rule


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The directional relationshipof I in the conductor, the

external magnetic field andthe force the conductorexperiences

I

F

B


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Motion of a current-carrying loop in a

magnetic field

N SL R

I

F

F Rotation

Commutator(rotates with

coil)

brushes


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Vertical position of the loop:

NS

Rotation


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Electric Motor

An electromagnet is the basis of anelectric motor

An electric motor is all about magnets and

magnetism: A motor uses magnets tocreate motion.

Opposites attract and likes repel. Inside an

electric motor, these attracting andrepelling forces create rotational motion.

A motor is consist of two magnets.


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Parts of the Motor

Armature or rotor

Commutator

BrushesAxle

Field magnet

DC power supply of some sort


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Motor Illustration
http://auto.howstuffworks.com/enlarge-image.htm?terms=motor&page=0


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ArmatureThe armature is anelectromagnet made by

coiling thin wire aroundtwo or more poles of ametal core.The armature has an axle,and the commutator is

attached to the axle.When you run electricity intothis electromagnet, it createsa magnetic field in thearmature that attracts andrepels the magnets in thestator. So the armature spinsthrough 180 degrees.To keep it spinning, you haveto change the poles of theelectromagnet.


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Commutator and Brushes

Commutator is simply a pair of platesattached to the axle. These plates providethe two connections for the coil of the

electromagnet.Commutator and brushes work together tolet current flow to the electromagnet, andalso to flip the direction that the electrons

are flowing at just the right moment.

Th t t f th t t tt h d t


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The contacts of the commutator are attached tothe axle of the electromagnet, so they spin withthe magnet. The brushes are just two pieces ofspringy metal or carbon that make contact withthe contacts of the commutator.
http://auto.howstuffworks.com/enlarge-image.htm?terms=motor&page=0


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Spinning Armature
http://auto.howstuffworks.com/enlarge-image.htm?terms=motor&gallery=1&page=1


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Example of Motor
http://auto.howstuffworks.com/enlarge-image.htm?terms=motor&gallery=1&page=2


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Answer the questions


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A current-carrying coil in a magnetic fieldexperiences a turning effect.

How can the turning effect be increased?A increase the number of turns on the coilB reduce the size of the currentC reverse the direction of the magnetic field

D use thinner wire for the coil


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What are the directions of the force in the leftand right loop?


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A student sets up the apparatus shown inorder to make a relay.

Which metal should be used to make the core?A aluminium B copper

C ironD steel

electric motor1

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