Magnetic FieldsMagnetic Fields

By: By:

Engr. Hinesh Engr. Hinesh KumarKumar

LecturerLecturer

I.B.T, LUMHSI.B.T, LUMHS

MagnetismMagnetismSince ancient times, certain materials, called Since ancient times, certain materials, called magnetsmagnets, have been known to have the , have been known to have the property of attracting tiny pieces of metal. property of attracting tiny pieces of metal. This attractive property is called This attractive property is called magnetismmagnetism..

NS

Bar Magnet

N

S

Magnetic PolesMagnetic Poles

The The strengthstrength of a of a magnet is concentrated magnet is concentrated at the ends, called north at the ends, called north and south “and south “polespoles” of the ” of the magnet.magnet.

A suspended A suspended magnet: magnet: NN-seeking -seeking end and end and SS-seeking -seeking end are end are NN and and SS polespoles..

NNSS

N

E

W

SNN

CompassCompassBar Bar magnetmagnet

S

N

Iron filings

MagnetismMagnetism is the force of is the force of ______________________ or or ______________________ of magnetic materials. of magnetic materials.

attractioattractionn

repulsiorepulsionn

Magnetic Attraction-Magnetic Attraction-RepulsionRepulsion

Magnetic Attraction-Magnetic Attraction-RepulsionRepulsion

N

SN

NS

S

NSNS

Magnetic Magnetic Forces: Forces: Like Like Poles RepelPoles Repel

Unlike Poles Unlike Poles AttractAttract

Magnetic FieldMagnetic Field• A field of force surrounding a A field of force surrounding a

permanent magnet or a moving permanent magnet or a moving charged particle, in which another charged particle, in which another permanent magnet or moving charge permanent magnet or moving charge experiences a forceexperiences a force

• The lines of force surrounding a The lines of force surrounding a permanent magnet or a moving permanent magnet or a moving charged particle.charged particle.

• Its a vector quantity. Its a vector quantity. 

• Its units: Tesla, GaussIts units: Tesla, Gauss

A A ____________________ ____________ is an area around a magnet that is an area around a magnet that applies a force to magnetic materials without touching applies a force to magnetic materials without touching them.them.

Magnetic FieldMagnetic Fieldmagnetic magnetic fieldfield

The magnetic field actually keeps going out forever, it just The magnetic field actually keeps going out forever, it just gets weaker the farther away from the magnet it is.gets weaker the farther away from the magnet it is.

It eventually gets too weak to move It eventually gets too weak to move anything.anything.

Magnetic Field LinesMagnetic Field Lines

N S

We can describe We can describe magnetic field magnetic field lineslines by imagining by imagining a tiny compass a tiny compass placed at nearby placed at nearby points.points.The The directiondirection of the of the magnetic field magnetic field BB at at any point is the any point is the same as the same as the direction indicated direction indicated by this compass. by this compass.

Field Field BB is is strong strong where where lines are lines are densedense and and weak where lines are weak where lines are sparse.sparse.

Properties Properties • Magnetic field lines are continuous and Magnetic field lines are continuous and

unbroken, forming closed loops. unbroken, forming closed loops. 

• A magnetic field line can never cross A magnetic field line can never cross another field lineanother field line

• Magnetic field lines are defined to begin Magnetic field lines are defined to begin on the north pole of a magnet and on the north pole of a magnet and terminate on the south pole.terminate on the south pole.

• If magnetic monopoles existed, then If magnetic monopoles existed, then magnetic field lines would begin and end magnetic field lines would begin and end on them.on them.

Field Lines Between Field Lines Between MagnetsMagnets

N S

N N

Unlike poles

Like poles

Leave N and enter

S

Attraction

Repulsion

ElectromagnetsElectromagnetsElectromagnetsElectromagnets

• An An electromagnetelectromagnet is formed when a is formed when a ________________ in an in an electric circuit is wrapped around an electric circuit is wrapped around an __________ __________ producing a magnetic field. producing a magnetic field.

• The magnet that results loses its The magnet that results loses its magnetismmagnetism if the if the electric current electric current ____________ ________________..

• Electric currentElectric current is simply the flow of is simply the flow of ____________________________..

(or the flow of charged particles, like electrons)(or the flow of charged particles, like electrons)

wirewireiron coreiron core

stops flowingstops flowing

electricityelectricity

GeneratorsGenerators

• A generator changes ________________________ energy into ______________________ energy when a coil of wire is rotated near a magnet..

mechanicamechanicall

electricalelectrical

NN

SS

Simple Electric MotorsSimple Electric Motors

A motor changes A motor changes ______________________ energy into energy into ________________________ energy by rotating energy by rotating

an electromagnet between an electromagnet between ______________ of a magnet. of a magnet.

electricelectricalal

mechanicalmechanicalpolespoles

NN

SS

How it worksHow it works::

• The coil of the electromagnet is connected to a source of The coil of the electromagnet is connected to a source of ______________________..

• When electricity flows through the electromagnet, a When electricity flows through the electromagnet, a ______________________ field field is produced. is produced.

electricitelectricityymagneticmagnetic

SSNN

NN

SS

NN

SS

• The rotating coil of wire can be _________ to an object to make it The rotating coil of wire can be _________ to an object to make it _____. _____.

Examples: ________ on an electric car, ___ blades, a ______ ____.Examples: ________ on an electric car, ___ blades, a ______ ____.

attacheattachedd

spinspin

wheelwheelss

fanfan

NN

SS

• The rotating coil of wire can be _________ to an object to make it The rotating coil of wire can be _________ to an object to make it _____. _____.

Examples: ________ on an electric car, ___ blades, a ______ ____. Examples: ________ on an electric car, ___ blades, a ______ ____.

attacheattachedd

spinspin

wheelwheelss

fanfan disco balldisco ball