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Exercise Page 200 Q5.1 Q5.2 Q5.3 Q5. 

Page 201 Q5.5 Q5.! Q5." Q5.# Q5.$ Q5.10 Q5.11 Q5.12 Q5.13 Q5.1 

Page 202 Q5.15 Q5.1! Q5.1" Q5.1# Q5.1$ 

Page 203 Q5.20 Q5.21 Q5.22 Q5.23 Q5.2 Q5.25 

Step 2: Read Study Material

%esson 1 & 'he ar Magnet ead this lesson

%esson 2 & *i+ole in a ,ni-orm Magnetic ield ead this lesson

%esson 3 & Magnetism and /ass %a ead this lesson

%esson & Eartha+oss Magnetism ead this lesson

%esson 5 & Magnetisation and Magnetic 4ntensity ead this lesson

%esson ! & Magnetic Pro+erties o- Materials ead this lesson

%esson " & Permanent Magnets and Electromagnets ead this lesson

Step 3: View Puzzle

Ple 1 6ie this +le

Step 4: MCQ Pratie TestMCQ 'est 1& Attem+t 1 7tart 'est

Step !: Re"ision Notes

e8ision 9otes 6ie

/alleries

Study Material

/o to&

The Bar Magnet

T#e $ar Ma%net

• 'he :ar magnet has to +oles similar to the +ositi8e and negati8e charge o- an electric di+ole.

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• ;ne +ole is designated as 9orth Pole and the other as 7oth Pole.

• <hen ss+ended -reely= these +oles +oint a++roximately toards the geogra+hic 9orth and

7oth Poles res+ecti8ely.

• %i>e +oles re+el each other and nli>e +oles attract each other.

• 'he +oles o- a magnet can ne8er :e se+arated.

T#e Ma%neti &ield 'ines

• Magnetic -ield line is an imaginary cr8e= the tangent to hich at any +oint gi8es s the

direction o- magnetic -ield at that +oint.

• 'he magnetic -ield lines o- a magnet (or o- a solenoid carrying crrent) -orm closed continos

loo+s.

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• ;tside the :ody o- the magnet= the direction o- magnetic -ield lines is -rom 9orth Pole to

7oth Pole.

• 9o to magnetic -ield lines can intersect each other. 'his is :ecase at the +oint o-

intersection= e can dra to tangents. 'his old mean to directions o- magnetic -ield at

the same +oint= hich is not +ossi:le.

$ar Ma%net as an E(ui"alent Solenoid

<e >no that a crrent loo+ acts as a magnetic di+ole. 'he magnetic -ield lines -or a :ar magnet and

a crrent carrying solenoid resem:le 8ery closely. 'here-ore= a :ar magnet can :e thoght o- as a

large nm:er o- circlating crrents in analogy ith a solenoid.

%et

i ? Crrent +assing throgh solenoid

a ? adis o- solenoid

2l  ? %ength o- solenoid

n ? 9m:er o- trns +er nit length o- solenoid

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%et @P :e the +oint at hich magnetic -ield is to :e calclated. Consider a small element o- thic>ness

dx o- the solenoid at a distance @ x  -rom ;.

9m:er o- trns in the element B ndx 

'he magnitde o- the -ield at +oint P de to the circlar element is gi8en :y=

4- P lies at a 8ery large distance -rom ; i.e.= r   a and r  x = then

'otal magnetic -ield at P de to crrent carrying solenoid&

4- M  is the magnetic moment o- the solenoid= then

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M  B 'otal nm:er o- trns D Crrent D Area o- crosssection

'his is the ex+ression -or magnetic -ield on the axial line o- a short :ar magnet.

'he magnetic moment o- a :ar magnet is ths eFal to the magnetic moment o- an eFi8alent

solenoid that +rodces the same magnetic -ield.

Study Material /o to&

Dipole in a Uniform Magnetic Field

orce on N +ole B mB= along

orce on S+ole B mB= o++osite to

<here=

m → 7trength o- each +ole

B → 7trength o- magnetic -ield

'hese eFal and nli>e -orces -orm a co+le= hich tends to rotate the magnet cloc>ise so as to align

it along .

'orFe acting on the :ar magnet=

τ B orce D Per+endiclar distance

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B mB D 9A

4n G9A7=

∴ 9A B 2l  sin H

9o=

τ B mB D 2l sin H

⇒ τ B B D (m2l ) sin H

τ B MB sin H

T#e Eletrostati )nalo%ue

• 'he magnetic di+ole moment o- a :ar magnet is gi8en :y

<here=

m → 7trength o- each +ole

2l  → %ength o- the di+ole

'he magnetic di+ole is analogos to an electric di+ole consisting o- to eFal charges o-

o++osite sign (I q) se+arated :y a certain distance . 4t has an electric di+ole moment=

• 'he eFations -or magnetic -ield ( ) de to a magnetic di+ole can :e o:tained -rom the

eFations o- electric -ield de to an electric di+ole :y ma>ing the -olloing changes&

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'hs= -or any +oint on axial line o- :ar magnet at a distance (d ) -rom the centre o- magnet=

7imilarly= eFatorial -ield ( ) o- a :ar magnet at a distance d = -or d   l =

Study Material/o to&

Magnetism and Gauss Law

• State*ent + 'he net magnetic -lx (Φ) throgh any closed sr-ace is alays ero.

• 'his la sggests that the nm:er o- magnetic -ield lines lea8ing any closed sr-ace is alays

eFal to the nm:er o- magnetic -ield lines entering it.

• 7++ose a closed sr-ace S is held in a ni-orm magnetic -ield .

Consider a small 8ector area element o- this sr-ace.

Magnetic -lx throgh this area element is de-ined as

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Considering all small area elements o- the sr-ace= e o:tain net magnetic -lx throgh the

sr-ace as&

Com+are this ith the /ass la o- electrostatics.

'he di--erence :eteen the /ass la o- magnetism and electrostatics is that isolated magnetic

+oles are not >non to exist.

Study Material/o to&

Earth&apos;s Magnetism

Eart#,s Ma%netis*

• -yna*o e..et ? 'he magnetic -ield o- earth has arisen de to electrical crrents +rodced:y con8ecti8e motion o- metallic -lids in the oter core o- the earth. 'his is >non as the

dynamo e--ect.

• 'he magnetic -ield lines o- the earth resem:le that o- a magnetic di+ole located at the centre

o- the earth. 'he axis o- the di+ole is +resently tilted :y a++roximately 11.3J ith res+ect to

the axis o- rotation o- earth.

• 'he 9orth magnetic +ole is located at latitde o- "$."J 9 and a longitde o- "1.#J <= a +lace

somehere in 9orth Canada. 'he magnetic 7oth Pole is at "$."J 7 and 10#.22J E in

Antarctica.

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'he +ole near the geogra+hic 9orth Pole o- the earth is called the 9orth magnetic +ole and the

+ole near the geogra+hic 7oth Pole is called the 7oth magnetic +ole.

• /eo%rap#i *eridian ? 'he 8ertical +lane +assing throgh the geogra+hic 9orth ?7oth

direction is called geogra+hic meridian.

• Ma%neti Meridian ? 'he 8ertical +lane +assing throgh 9 ? 7 line o- a -reely ss+ended

magnet is called magnetic meridian.

Ma%neti -elination and -ip 0r Ma%neti Ele*ents

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• Ma%neti ele*ents ? 'he +hysical Fantities= hich determine the intensity o- earths total

magnetic -ield com+letely (:oth in magnitde and direction)= are called magnetic elements.

• 'here are three magnetic elements o- earth&

o Ma%neti delination ? *eclination at a +lace is the angle :eteen the geogra+hic

meridian and magnetic meridian. 4t is denoted :y θ.

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o Ma%neti inlination or dip ? *i+ at a +lace is de-ined as the angle made :y the

direction o- the earths total magnetic -ield ith the horiontal direction. 4t is denoted

:y δ.

o orizontal o*ponent o. eart#,s *a%neti .ield ? 4t is the com+onent o- earths

magnetic -ield along the horiontal direction. 4t is denoted :y BK.

4n the -igre= -or rightangled triangle A%P=

BK B B cosδ L (i)

Also=

B6 B B sinδ L (ii)

7Faring and adding the eFations (i) and (ii)= e o:tain

*i8iding eFation (ii) :y (i)= e o:tain

Study Material/o to&

Magnetisation and Magnetic Intensit

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• Ma%neti intensity ? 4t is gi8en :y the relation=

<here=

B0 → Magnetic -ield inside 8acm

0 → N D 10?" 'mA?1

74 nit → Am?1

• ntensity o. *a%netisation ? 4t is de-ined as the magnetic moment de8elo+ed +er nit

8olme hen a magnetic s+ecimen is s:Oected to magnetising -ield. 4t is denoted :y I .

74 nit → Am?1

• Ma%neti ndution ? 4t is de-ined as the nm:er o- magnetic lines o- indction crossing +er

nit area throgh the magnetic s:stance. 4t is denoted :y B.

Magnetic indction B is the sm o- the magnetic -ield B0 and the magnetic -ield 0I  +rodced

de to the magnetisation o- the s:stance. 'hs=

B B B0  0I  B 0H   0I 

B B 0 (H   I ) L(ii)

• Ma%neti susepti5ility ? 'he magnetic ssce+ti:ility o- a magnetic s:stance is de-ined as

the ratio o- the intensity o- magnetisation to the magnetic intensity. 4t is denoted :y χ m.

• Ma%neti per*ea5ility ? 'he magnetic +ermea:ility o- a magnetic s:stance is de-ined as

the ratio o- the magnetic indction to the magnetic intensity. 4t is denoted :y μ.

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9o= on di8iding :oth sides o- the eFation :y H = e o:tain

rom eFation (iii)= e ha8e

Koe8er=

Study Material/o to&

Magnetic !roperties of Materials

• Materials can :e classi-ied as diamagnetic= +aramagnetic= or -erromagnetic on the :asis o-

ssce+ti:ility ( χ ).

-ia*a%neti Para*a%neti &erro*a%neti

?1 χ  0 0 R χ R ε  S 1

0  μr R 10 1 R μr R 1 ε  r 1

R 0 0   0

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Kere= T is a small +ositi8e nm:er introdced to Fanti-y +aramagnetic materials.

• -ia*a%netis* ? *iamagnetic s:stances are those hich ha8e a tendency to mo8e -rom

stronger to the ea>er +art o- the external magnetic -ield.

o <hen a :ar o- diamagnetic material is +laced in an external magnetic -ield= the -ield

lines are re+elled or ex+elled and the -ield inside the material is redced.

o Ex+lanation o- *iamagnetism ? *iamagnetic s:stances are the ones in hich

resltant magnetic moment in an atom is ero.<hen magnetic -ield is a++lied= those electrons ha8ing or:ital magnetic moment in thesame direction slo don and those in the o++osite direction s+eed +. 'his ha++ensde to indced crrent in accordance ith %en la.'hs= the s:stance de8elo+s a net magnetic moment in direction o++osite to that o-the a++lied -ield and hence= re+els.

o Exam+les o- *iamagnetic materials ? ismth co++er= lead= silicon= nitrogen (at 7'P)=

ater= and sodim chloride

o Meissner e--ect ? 7+ercondctors exhi:it +er-ect diamagnetism. A s+ercondctor

re+els a magnet and is re+elled :y the magnet. 'his +henomenon o- +er-ectdiamagnetism in s+ercondctors is called the Meissner e--ect.

• Para*a%netis* ? 7:stances that ha8e the tendency to mo8e -rom a region o- ea>

magnetic -ield to strong magnetic -ield i.e= they get ea>ly attracted to a magnet

o Ex+lanation o- +aramagnetism ? 'he atoms o- a +aramagnetic material +ossess a

+ermanent magnetic di+ole moment o- their on. ;n accont o- the ceaseless random

motion o- the atoms= no net magnetisation is seen. 4n the +resence o- an external -ield

B0= hich is strong enogh= and at lo tem+eratres= the indi8idal atomic di+ole

moment can :e made to align and +oint in the same direction as B0.

'he -ield lines get concentrated inside the material and the -ield inside is enhanced.

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o Exam+les o- +aramagnetic materials ? Alminim= sodim= calcim= oxygen (at 7'P)=

and co++er chloride

o Cries la ? Magnetisation o- a +aramagnetic material is in8ersely +ro+ortional to the

a:solte tem+eratre T .

<here= C is called Cries constant

• &erro*a%netis* ? 7:stances hich get strongly magnetised hen +laced in an external

magnetic -ield

o Ex+lanation o- erromagnetism ? 'he atoms in a -erromagnetic material +ossess a

di+ole moment aligned in a common direction o8er a macrosco+ic 8olme called

domain. Each domain has a net magnetisation.

<hen e a++ly an external magnetic -ield B0= the domains orient themsel8es in the

direction o- B0 and simltaneosly the domain gros in sie.

o 'he -erromagnetic +ro+erty de+ends on tem+eratre. At high tem+eratre= a

-erromagnet :ecomes a +aramagnet. 'he tem+eratre o- transition -rom

-erromagnetic to +aramagnetic is called the Crie tem+eratre (T C). 'he ssce+ti:ility

in the +aramagnetic +hase is descri:ed :y=

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o Kysterisis

 

'he a:o8e gra+h shos the :eha8ior o- the material as e ta>e it throgh one cycle o-

magnetisation.

An nmagnetised sam+le is +laced in a solenoid and crrent throgh the solenoid is

increased. 'he magnetic -ield B in the material rises and satrates as de+icted in the

cr8e Oa. 9ext= H  is decreased and redced to ero.

At H  B 0= B U 0 (cr8e ab)

'he 8ale o- B at H  B 0 is called retenti8ity.

9o= the crrent in the solenoid is re8ersed and sloly increased. Certain domains are

-li++ed ntil the net -ield inside stands nlli-ied. 'his is re+resented :y the cr8e bc .

'he 8ale o- H  at c  is called coerci8ity. As the re8ersed crrent is increased in magnitde=

e once again o:tain satration (cr8e cd ).

9o= the crrent is redced (cr8e de) and re8ersed (cr8e ea). 'he cycle re+eats itsel-.

or a gi8en 8ale o- H = B is not niFe= :t de+ends on +re8ios history o- the sam+le.

'his +henomenon is called hysterisis.

Study Material/o to&

POST Lesson 7

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!ermanent Magnets and Electromagnets

• 'he s:stances hich at room tem+eratre retain their -erromagnetic +ro+erty -or a long

+eriod o- time are called +ermanent magnets.

• 'he ma>ing o- +ermanent magnets is an old art. ;ne can hold an iron rod in the 9orth?7oth

direction and hammer it re+eatedly.

• ;ne can also hold a steel rod and stri>e its one end ith a :ar magnet continally to ma>e it a

+ermanent magnet.

• An e--icient ay to ma>e a +ermanent magnet is to +lace a -erromagnetic rod in a solenoid

and then +ass crrent. 'he magnetic -ield o- the solenoid magnetises the rod.

• 'he material sed -or ma>ing +ermanent magnets shold ha8e high retenti8ityVso that the

magnet is strong= and high coerci8ityVso that the magnetisation is not erased :y stray

magnetic -ields= tem+eratre -lctations or minor mechanical damage.

• 7ome sita:le materials -or ma>ing +ermanent magnets are alnico= co:alt steel and ticonal.

Eletro*a%nets

• 'he core o- an electromagnet is made o- -erromagnetic materials= hich ha8e high

+ermea:ility and lo retenti8ity.

• 'he most sita:le material -or ma>ing an electromagnet is so-t iron.

• y +lacing a so-t iron rod in a solenoid and +assing crrent= the magnetism o- the rod can :e

increased thosand -old.

• Electromagnets are sed in electric :ells= lods+ea>ers and tele+hone dia+hragms. /iant

electromagnets are sed in cranes to li-t machinery and :l> Fantities o- iron and steel.