Physics Preston Notes

8/6/2019 Physics Preston Notes

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gHAPTER

WAVES

tn Understandingaves1 An oscillatingystem uch sa simple endulumr a

loaded pring wingso and roabout fixed osition.AmplitudeA) s hemaximumisplacementinmeter)ftheoscillation.eriodT) s he ime insecond)akenocompletene ycle f heoscillation.requencyf) s henumberinHertz) foscillationshat ccurnoneperiod.

t 1Therefore, fT orT= r

2 A wavemotion s th ephenomenonf energyransferfacilitatedy heoscillationfmoleculesfamedium.f hevibrationf hemoleculessperpendicularo he irectionfthewavemotion,hewavescalled ransverseavesuch

aswaterwave).f themoleculesibraten parallelo thewavemotion,hewave sknown sa longitudinal ave(such ssound ave).

3 Graph shows displacement-distanceraph f a wavemotion. avelengthinm) s hedistanceccupiedyonecompleteycle f hewave.

DisplocementDistonce roph A)

Amplitude

(' )

DisplocementTimeGroph(B )

Amplitude

(m)

1 wove velocity= 2-r ms-r

Graph showsdisplacement-timeraph fawave.Wavevelocityinms-1)s henumberfwavelengthsor istance)thewave dvancesnone econd.

Wavelength, frequencyandwave elocityare elatedin hewaveormula: = l.A wavefrontsan maginaryurfaceoiningll hepointsnspacehatare eachedt th esame nstant y a wavepropagatinghrough medium.na plan iew, aves reoften epresentedn diagramsy a series f l ines fwavefront.hedirectionsf thepropagationf hewaveswhich re erpendicularo hewavefrontsre suallyhownassmall rrows.

l ml

i''l,on." 6

Wovefronts

Afterhe nitial isturbance,noscillationystem il leither

carry ncontinuouslyr slow own nd top ventually.n

the irst ase,he ystems n esonanceroscillatingt tsnaturalrequency. physicalystemmayhave everalnaturalrequenciestwhicht canvibrateasily ith erylittle dditionfenergyrom nexternalource. henevertvibratest oneof tsnaturalrequencies,t ssaido be n

resonance.n he ater ase,hephenomenons known sdamping hich suallyccursn hepresencef friction.

Frictioncts gainsthemotionndprogressivelyeduces

theosci l lat ionmpli tudelthoughhe requencyf hevibrationemainsnchanged.Phenomenauchas reflection,efraction,iffractionndinterferencereobservedhen wavemeets nobstacle

orawavemeets ther aves.he ules fsuch henomenareapplicableo all ransversend ongitudinalavesincludingight,ound ndwater aves.

@ Analysing eflection

1 The awof reflectiontateshat heangle f ncidenceequalso heangle f eflection.Examplesf eflection:

Incidentolwoves

Normql

; reflected woves- - J - - -

I

The requency,avelengthnd peed f hewave emainthesame fterhe eflection.owever,hedirectionf hewavewillchangend hereforehevelocity illalso ifferafterhe eflection.

(s)

Time

. r m



tf,l Analysing efraction

1 The efractionf waves anbedemonstratedna rippletank ychanginghewater epth tvariousegionf hewaterank.When ater avesravelrom deeperectiontoa shallowerection,t s efracted.hewaves ovelowlyinshallowaternd he eductionfspeedauseseductioninwavelengthhi lehe requencyemainsnchanged.

Wavefrontslose pon each ther nd hewaves en dtowardshenormalf he ntersection

4 Variousiffractionatterns:

2

@ Analysing iffraction

Th e henomenonfdiffractionccurshen ither smallobstacleranobstacleith narrowpeningsplacedn

thepath fprogressingavesna rippleank. he ffect fdiffractionssignificantnlywhenhe ize f heobstaclerthegapof heobstaclesvery mallncornparisono hewavelengthf h ewaves,The requency,avelengthnd peed f hewavesemainthesame fterhediffraction.owever,hedirectionf hewaves ill hangend hereforehe elocityil l lso ifferafterhediffraction.hewaves pread utas hey ass

through narrow apand hereforeheshape f thewavefrontshangesfterhediffraction.Lightsalso iffractedhent spassedhroughnarrow

slit. ut he ffectsonly oticeablehe nhe li twidthsnomorehan ne-hundredthfamillimetersuggestinghatightsarewaves ith erv hortwavelenoth.

- f

'.r

t-+

}.

i - - - 2

Variousxamplesf efraction:

3F| Analysingnterference

1 Interferenceccurs' ,- :- , ' , - ' - - ' . , ' ,, :s

t h e s a m e m e d i u mt ' : : = - . : - : ' - =. ' , , =i .e.hey avehe arr ie-i : -=- . . . . : :- : ' .

complexpat ternf rr - ' .? ' - : : - : . - - .

p r i nc i p l ef superpos i t i on: : : ' - :

t h roughach the r' , ^ : - : : - : : : ' -

d isplacementofheme: - = ' - . : . - " -

s imp l y theum f he : . : - : : : : : :2 Anexper imentnownsYc. ' : s : : - :

can e arr iedut ode-: -: : '=:

lf he istanceehvee'perpendicularistar:nodes.hewavelencr:

o fampl i tudehi le i r : - . : . , - : " : -

t h e y a n c e la c h t h e r : - : : ' , : - : -



fE| UnderstandingoundWaves

Sound aves hich re ausedyvibrationsfasubstance,.g. speakerone, re ongitudinalnnature.hemoleculesfai rwobblenadirectionarallelo he irectionf he ravelingound.ound av e eedsmediauchasair,water nd oncreteo ravelhrough.tcannoto hroughvacuum here edia onotexist. 66$eedofsoundnvariousediaiffers.ts peedndry ir at oc),inwaterat0'c)an dnconcretere 00ms-1,1400s- land5000ms-1 espectively.Differentrequenciesoundifferento he ar . ighrequenciesre eardshigh itch otes hileow requency

soundsre aidobeof ow itch.ound aves ithargemplitudeppearobe oud n he arwhileoundshichhave mall mplitudere aidobesoft.Reflectionrecho fsoundrovideswa yomeasureistance.he quations

(speedfsound)= 26 (twicehedistanceromhe ourceo he eflection)t (theimehe oundakeso ravel acko he oure,e)

Gl Understandinglectromagneticaves

The lectromagneticpectrumsa continuousequencefall nownypes felectromagneticadiation,rrangedbywavelengthangingrom he hort osmicayshroughammaays, -rays,ltravioletadiation,isibleights,infraredadiation,icrowaves,o he ongwavelengthsf adio aves.Electromagneticaves ave roperties

uch swavelength,mplitude,requencyndpower.hey reelectric,magneticnd ransversennature.hey an ravelhroughree pacenstraightines ta speedfapproximatelyx 108ms-1(commonlynowns he peeof ight).he nergyfanelectromagneticaveadiatingrom sourcediminishess t ravelsutwardsnd s nverselyroportionalo he quaref tsdistanceromhesource.Wavelengths,ypes ndheirespectivepplications:

Wavelengthm) 104o3 x 10-1m 10r to 3 x 10-1m 10{ o10rm 4 x 10'7o7 x ' 1 0 tm

TypesfWaves Radio aves adio, Microwave Infrared Visibleights

Applications TV elecommunicationselecommunications,i'adar,ookingven

Thermography,night ision,eatingdevice

Vision,hotosynthesis,photography

Wavelengthm) 104o10rm 10-11o104m 10-14o 10-11

TypesfWaves Ultravioletights X-rays Gammaay s

Applications Moneynspection,terilisation,pesterminator

Radiography,adiotherapy,wieldingnspection

Destroyancerell, terilisation,Pesterminator



gHAPTER

ELECTRICITY

123

4

5

67

@ Analysing lectricFieldsand ChargeFlowBasicallyhere re wo yp es f electricharges:+)positivehargend -)negativeharge.TheS.l, nitorelectrichargesCoulombC) .The hargefa protonspositive+1.6 10-1e)and he hargefanelectronsnegative-16x 10-1e).Aneutronas ocharge0C)and sconsideredeutral.nobject hich as higherumberfelectronsil lthereforeea negativelyhargedbject. ome bjects hen ubbedose rgain lectronasily nd husbecomeegativelyhargedrpositivelyhargedfterubbingit h notheratedal.Eiectricurrentepresentshemovementfelectrichargesndsdefineds he ate f low felectricharge.

The ormulaor urrentI) s =f wnere s he uantity

ofchargenCoulombnd is he ime urationnSecond.TheS.l. nitor urrentsAmpereA) nd A= 1Cs-1.Ina solidonductor,lectronsre lowingromhe egativeerminalo he ositiveerminal.ut yconvention,th e irectionf currentlow sconsideredlowingro mhepositiveo henegative.

8 Electrichargesnteractit h ac h ther.ike hargesepel hile nlikehargesttract.ines f orce rawnfrom ositivehargeo negativehargesusedo representuc hnteraction.nan areawhereheres adistributionfelectricharges,uchines f orceorm nelectricield. he ines fanelectricield i l l rovidean ndicationf he ath fa positivehargef t s reeomoven he ield.

9 Examplesfelectricields:

Effect f e lectr icie ldon chorge ing-pong ol lexperiment.

(o) (b )

r=t 7- F.t u \ Fll-6. ll l,l ,brll - l -F l * l I - l F : l * ll - I l + l l - | l + l? . - - r - + +

l - + l l - + l+H .V .+ +H.V.+

Effect f e leclr icie ldon chorge ondle lome.

(.) l-+l Fl+ 597/l-l

l l lKryt-tl * l J ( l - lf / \ i

Tl + l+ H . V . +

13



CurrentandPotentiatDifference

1 Potentialifferencep.d.)etween'twoointsnanelectric

fields hework eededomove unit hargerom ne oint

toanother.2 Theormulaorp.d.(V)sV= { wnereW s hework one

inJoule ndQ squantityfchirgenCoulomb.

3 TheS.l.unitorpotentialifferencesVolt V)and1V=1JC-1.

4 Ohms aw tateshattheotentialnergyV) crossmetal

conductorsdirectlyroportionalo thecurrentI) lowing

@ Analysing elationshipetween

O K Tc Temperoture

throught providedhe emperaturend ther hysical6p Analysing Series and parallel

conditionsemainonstant:Circu i ts

1 The esistorsn heFigurere onnectednseries.

+ V r - + V z - + V s -

The .l. nitor esistancesOhm A)and Oh m 1VA-1.Factorsffectinghe esistanceR)of a conductornclude

its ength/) , tscross sectionalrea A) , tsmaterial

(resistivity)andts emperature0).p =O*

q)()o.2

o)E

i.e. - | or L =constant.I

5 The onstantf ) .nrtsentshe ppositionf he onductor

materialo he lectricurrentlow ndsgiven name alled

Resistance.he ormulaorResistanceR)sR=f

where

V sp.d.nVolt nd scurrentnAmpere.

67

R{O ) R ei)

L,(,,.inLf,,^.,tR (O )

(current)

1,.l./(

-]----------------- Temperorure' 0fc)

The esistancef a conductoril ldrop n andem ith tstemperature.he esistancefsomematerialsil l venal l

tozerowhents emperatures oweredo a certainegree.Suchmaterialsre alleduperconductors.ecausefzeroresistance,lectricalunent ill loworeverna closedooponcet sset nmotion.

The ame urrentlowshroughach f he esistors.l = 1 , , = l r = 1 ,Th e um f he .d. crossachesistorqualso he .d. fthe ource. =V,+V2+ 3Th e ombinedesistancef he esistorsnseriesqualsothe um f he esistancefall he esistors.= R,+ R,+ Rr .Th eeffectiveesistancencombinatrons hereforelargerha nhe esrstancefeachesistorn tsown.The esistorsn heFigurere onnectednparallel.

The ame .d.sactingOol'r..ur.nf he esistors.=Vr=

Vr=V,The urrentfromhesourcequalso hesum fcurrentsflowingneachesistor.= ,+ r+ ,The eciprocalf he ombinedesistancef he esistorsinparallelequalso he um

f he eciprocalsf he esistance1 1 ' l , Iof eachesistor.R-

=Ri

*R;

*R; . Theeffective

resistancen combinations thereforemallerhan heresistancefeach esistorn tsown.

Superconduc 'c .

;T l+ Y t -

, R : tL------:____l

+ V r -

t4



@ Analysing lectromotiveorceand nternalResistance

Electromotiveorce re.m.f.nshorts hepotentialfanelectricourceomove lectrichargeshroughcompletecircuit.he .m.f. f he ourcendicateshe otal nergyhesourcescapablefgivingoeach nit harge.lnternalesistancef a cellor an electricource xists

becausef hepropertiesf tselectrolytend/ortselectrodeconnections.henternalesistancesusuallyuiteow;e.g.about .5Ohmsora dry ell.Owingo heeffect f he nternalesistance,hep.d. crosstheerminalsfacellwillvaryn elationo he oad onnectedto t. nanopen ircuit,heresno oad ndnocurrentlow,thep.d. crosshe nternalesistanceszero nd ence.dacrosshe erminalqualso hee.m.f. f hecell.n hecase fa oad,herescurrentlowesultingcertainmountofvoltagerop crosshe ntemalesistance.encehe .d .acrosse erminalil l e owerhanhee.m.f.f he ell.RefertoheFigure,=E I rwhere s he .m,f., s hep.d.

crosserminals,is hecurrentlowingnd is heinternalesistance.

i - - - - -- - - - - r

ffil Anatysing lectricalEnergyand

Power1 Electricalnergys heelectricalotentialnergyained

byachargenanelectricource.scurrentlowshroughload,heelectricalotentialnergyf he harge ill e ostandsconvertedootherorms fenergyuch sheat,ightor sound. he ate twhich uch nergyransformationstakinglacesdefinedsElectric ower.

2 The ormulaeorelectricalnergyE)and lectricowerP)are espectively:E =VQwhere s he .d.nVolt, s he uantityfcharge

inCoulomb

P =

+

whereis he ime urationnSecond

34

TheS.l.unitof Electdc owersWaft W)and1 Watt=1 Js-1.Theunit fenergy easurementsed yTNB orelectricalconsumptionsKilowatt our kwh).On e ilowatt-hoursinequivalenthe nergyuppliednone ouroanelectricalappliancehose owersonekilowatt.rom 006 une,TNBschargingrate f 21.8 ents erunitor he irst 00units. ate f28.9 entser nit ill e hargedor nit 01to 1000 ndwhen onsumptionxceeds000 wh,31,2

cents ill e eviedneach nit.Typicalomesticppliancesan d heir lectricalower)inc lude:nergy-saveright u lb 17W), ungstenu lb(40-100 ), luorescentube 2040W), adio10W),fan 60W), V 80-140 ), ridge100-130),d t npair-conditioner800-950), ice ooker500-800)"andaterkettle2000W).Efficiency"r)ofanelectricalpplianceanbedefineds

useful nergyutput./

't-l=

T =

total nergynput

usefulowerutput

x 100%

x 1 0 0 %

of

o

total owernput

An energy-saveright ulb s more nergy ff ic ientncomparisono a tungsten-f i lamentight ulb ecausetrequiresess nergynputoproducenequal mountfl ight.

7 Ways o i nc rease f f i c i encyn domes t i cne rgyconsumption:a) Switchtof fwhen ot nuse. se imerfpossible.

b) Doenergyfficiencyomparisoneforeurchase.electonewitha size/capacityhatmeets ournormal eed.Useenergy aving lternative s;.g. luorescentubeinsteadf ungstenulb nd olar oweredeaternstead

ofelectricaleater

c) Avoid xcessivesageuch ssettinghermostatfair-conditionerr efrigeratortveryow emperature.

d) Keep ppliancesngood ondition;.g, leanilter ndreplacerokenoor eal.

e)Avoid astage;.g. oil namounthat ou eednsteadof a fullkettle r avoidrequentpeningf refrigeratordoor rprovideoodnsulationorair-conditionedoom.

15



gHAPTER

ELECTROMAGNETISM

m Anatysinghe Magnetic ffectof a Current-carryingConductorAnelectromagnetsa emporaryagnetausedy urrentlowingna conduc-tor.The atternsfmagneticield roCucedycurrent-carryingonductorsependon he hape f he onductorssshownnFrgureelow.

(o )A long t ro igh t i re (b)A s ing leoop (c )A solenoid

The ight-handrip ule tateshatf he ight and rips coi l fwire i thhefingersn he irectionf he urrentlow,he humb il l ointo he orth ole fth eelectromagnet.The trengthfmagneticield fanelectromagnetncreases,vitha) he umberof urnsn hecoil,b)a largerurrentnd c) he ype f core uch s ron,ferromagneticaterial.

5 Appl icat ionsf electromagnetncludeagneticelay,lectr icel l , ar ieceand ircuitreaker.

ff,| Understandinghe Force n a Current-carryingConductor n a MagneticField1 When nelectromagnetsplacedear magnet,he nteractionf womagnetic

fields roducesorce n he onductorsshownnFiqureelow.

ht

ffi@-'l

Fleming'seft-handule tateshat f he humbnd irstwo ingersf he eft-hand reheld tright ngleo each ther,he humb iveshedirectionf heforce,he orefingerhowshedirectionf magneticield nd hemiddleingerpointsn hedirectionfcurrent.Themagnitudef he orcencreasesit h(a) he trengthf hemagneticield,(b) he ize fcurrentnd(c) he engthf he onductor.

26

4 Asimple.C. otornFigureelow

showshe urningffectfa coupleor wo ppositeorcesctingn wosidesf he oi l inhemaqnet ic f ie ld.

5 Thes p e e d f ro ta t i on f a D .C .motora' :e a' . . ' . : cvchanginghe

force f :^e : : - : e ihestrengthf

rnagnet ice a ' . 'eS:Ze fcurrentr

the engt r ' : 'e :c , or he urn ing

effect\ \ 'c: ' ' :^e c i t

, 3

Commulo t o r

f f , | Anaiysing lectro-magnet icnduct ion

M a g n e t i c n d u c t i o n s t h ep h e ^ : - e ' c ^ l n a t a r e l a t i v e

A ' ^ A I T A Ar r v ! E s . - s . , , s c l ' a W I f ea n O a

magnei 'e 'J producesne.m. f .ni h o , . o

Nlag, ie:' l - : t on scausedYchangen nemagnet icluxonacondr, lc tornd tsmagni tudethe,ncjuced- f ) ncreasesitha)herate fchangef hemagneticlux,(o he irengthf h emagneticieldand c) he engthf he onductor.Fa raday ' saws ta tesha t heinduced.m. f .n a conduc torsdirect lyroport ionalo the ate twhichheconductoruts hrough

l ines f h emagneticield.Lenz's aw tateshat he nducedcurrentlwayslowsna directionsuchha ttopposeshe hangeha tiscausingt.Fleming'sight-handule tatesthat f the humb nd irst wo ingersof the ight-handreheld t r ight



l A

angleo each ther, iddleingerpointsn he irectionf h e nducedcurrent,he oref ingerhowshedirectionf magneticield nd hethumb iveshedirectionf he orce.App l i ca t ionsf e l ec t romagne t ici nduc t i onnc lude.C. ndD.C.generatorshichonvertechanical

energynto lectricityy he otationofconductoroilsnamagneticieldas shownn Figurea)and b)asshownelow.

A s imp le .C.genero tor

Adirecturrentlwayslowsnoned i r e c t i o nn d t h a s c o n s t a n ta m p l i t u d eh i l e n a l t e r n a t i n gcu r ren t l ows n twooppos i tedirectionslternativelyta constant

frequency.The mplitudefanA.C. oltageanbespecifiedn hree ays:(a)peako peak V* o valuee-

tween aximumndminirnum);(b)peakV^ value etweenaxi-

mum nb ero);nd(c) oot-mean-squar€V,,". hich

giveshe ame mountfpowertransfersa D.C. f th esamev a l u e ) . V 2 x V a n d V =

V ' P ' P P r ' m . s .p

\T

h e

O f

\ / o

a

i n

n

U J

v

ane

d

h eI J

^ +

g n

ffil AnalysingTransformers

1 Mutualnductions he lectromag-neticnductionf a coi lwhent splacedearoanotherhichas nalternatingurrentlowingn t .

A s imp le .C.genero tor

In dealransformer,=.

Vo--N; '

V"l.= ^l^ nd tsefficiencys s P Pv l

- l l . ' o / , , P P= 1 U U % rv t

= 1 0 0 % .

A transformeronsistsfaprimary

coi l nda secondaryo i lwoundaroundcommonore hichasses

the lux rom heprimary oil oandthroughhe econdaryoil.A step-downransformerasahigherumberf u rnsNo)n tsprimaryoilandan nput oltageVo)

willproducelower utputoltageat ts econdaryoi lwhi lestep-uptransformeras higheru,mberfturnsN,) nsecondaryndalsoh ighe ru tpu to l t ageV" )n t ssecondarvoil.

Mos t l ec t r i c i t ys p roducedygenera to rsr i ven y ro ta t i ng

turbines hichmay e urned ys team.wa te r .w ind o r o the rintermediatenergyarrier.A ransmissionystem onsistsf(a)a first tage fvery igh oltage

overheadinesve ron g istancee-

tween tep-upransformerst thepower lant nd heNationalr idNetwork,b)severalntermediatestagesrom heGrido substationsthrou h step-downransformersndoverheadablesnd c) as t tage

of distributionhichs hedeliveryfrom ubstationso heconsumersthroughverheadr undergroundcables.I n p o w e rr a n s m i s s i o n ,. C . sp re fe r red ve rD.C.because

transformersanbeusedoobtainhigh ol tagesor hepurposefachievingmallerurrentlow ndlowernergyossn he ransmssioncables.Most f hepowereneratedn hecountrys suppledo heNationalGridNetwork ith hepurposefbetterontrolnd igherfticiencyndistr ibut ionndalsomore el iablesupplyn heevent fa local lantfai lurermaintenance.

Shortagesf energyuels reateeconomicndpol i t icalr is is hichaffecthe ifeof everyonendherebymake s ealizehe mportancefarenewablenergyource.The mpactshat r imaryower

olants ave n theenvi ronmentinc lude(a) uclearowerlantsollutinghe

a tmosoherei th ad ioac t i venucl ides,

(b) ossil-fueledlantsausingcidrain nd lobalarmingnd

(c)hydroelectr icams rast ical lyalteringandscapend cologyflife vstems.

I n p r a c t i c e ,n e r g y o s s i n

transformersccursue o oartialf luxinkagen he oi lsnd lso eatlossrom onductoresistance,romeddy urrentndmagnetizationnddemagnetizationf he ore.Ways o improverans fo rmereff ic iencynclude(a ) singhickeroi l ir eo owerhe

resistance,(b)usinghin heetsf aminated

coremater ia lo reduce ddycurrent,

(c)using oftmagneticaterialoreduceoss rommagnetizationand emagnetizationnd

(d) singclosedoop esignor hecorenadditionoan rrangementof windingne oi l roundheothero mproveluxinkage.

UnderstandingheGeneration ndTransmissionfElectrici ty

Sourcesfenergyor

generationfelectricityreeither onrenewable

sourceshichre uclearowerndfossi luels r renewableourcessuch s hydropower,ind ower,so la rpower nd ene rgyrombiologicalrocesses.

27



,i1i"""""""""""""""RfrPHICORGfrIIlSER3'|::::::::::::::::::::::::::::::::i:i:

r::: Name the rules n Box A, B and C. Complete he equations n box D and E

Renewable energ"ysources Nonrenewable energy sources

Power Tlansmission National Grid Svstem

38

ELECTROMAGNETISM

Analysing the Magnetic Effect of a Current-carrying Conductor

-€-_------- Northolei

CurrentI

Understanding the force on a current-carrying Conductor in a Magnetic Field

B MogneticT

field ,/ |

-Force Itl

Current

Analysing Electromagnetic Induction

field rr | |

\ |

Inducedurrent \l I____l

Analysing Tbansformer

Ideal transformer IV I

p _ |

\= l IV l = Ip

IV I I

n = 100 x7-!\ Vo= Vo I\ / l

Understanding the Generation and Thansmission of Electricity



gHAPTER

ELECTRONICS

o fe

r

I

e

e rk l

@ UnderstandingheUses f the C.R.O.

1 A materialives ff hargedarticleswhen t is heated o a hightemperature.hisscalledhermionicemissionndhe articlesre alledthermions.

2 The hermionsmit tedncreaserapidly ith especto emperature.

3 A typicalhermionicpparatusastwospaced-outlectrodesnsidegas-filledlassube.

4 On emetal late erves sanodewhile nothertypicallytungstenfilamentra coatedilamentrelsea metalp latecoatedwi th acompoundf i t hasa separatefilament)ervesscathode.

5 Anelectricalupplys used or hefi lamenteatinghi le high .d.supply s put across he twoelectrodesopromotelectronlow.

6 A galvanometern series it h hecircuit easureshe urrentlow.

7 Byheat ingornot) he i lamentcoupledith hanginghepolarities

of he igh .d . crosshe lectrodes,experimentanbecarriedut oconfirmheemissionfelectrons.

8 Cathodeaysarebeams f fastmovinglectrons.

I Thepropertiesf cathodeayarestudiedhroughariousathodeaytubesC.R.T.)suchs he Maltesecrossube,hedeflectionubeandthePerrinube.

10 lt spropertiesnclude:

. lt movesna straightin e

. lt possessesegativeharge

. l t possessesomentumndenergy

. lt sdeflectedya magneticield

. lt is deflectedyanelectricieldan d

. lt producesluorescencehentstrikes uminescentcreen.

11 The tructurefa cathodeay scilloscopeC.R.O.)sshownnFigureelow.12 lt has hreemain arts:nelectronun, deflectionystemnd fluorescent

screen.13 Anelectronunconsistsfa filamentforheatinghecathode;cathodeto

produceathodeay eams);wire rid to educehe mountfelectronsoingthroughnd rightnessontrol)nd woanodesoneoaccelerateheelectronsand notheror ocus ontrol).

14 A deflectionystemonsistsf wosets fparallellateso controlheverticalandhorizontaleflectionsf hebeam.

15 The nner urfacef he ube oated ith in c ulphideormshe luorescentscreenwhichonvertsineticnergyo ight).

16 Lightsemittedy ha tmaterialt he nstanthat lectronsit t.17 Anoscilloscopesbasicallydevicehich isplaysgraphfanelectricalignal

and tshowsow ignalshangeve rime.18 Commonsesnclude easurementf voltages,easurementf shortim e

intervalsr requencynd isplayfwaveforms.

@ Understandingemiconductoriodes

1 Asemiconductorismaterialhoseonductivityies etweenhat fa metalndan nsulator.

2 ltsconductivitysaffectedy emperature,xposureo ight nd tscontentfimpurities.

3 The uter rbitsf he tomsfa materialndhe umberfelectronsnhabitingin he m eterminehe onductivityf hematerial.

4 The uter rbitsan edividednto nergyands:conductionand nd valenceband ith nenergyap eparatinghem.

5 Asemiconductoras ully ccupiedalenceand ith smallenergyapo heconductionandmakingta poor onductor.

6 But lectronsn he alenceand an cquireufficientnergyfromncreasentemperaturerexposureo ight)o ump crosshe ap omoven he onductionband nd onductlectricity.

7 Examplesfsemiconductorsncludeiliconnd ermanium,ach fwhich asfour lectronsn he uter rbit f he alenceand.

8 Asiliconrgermaniumto man harets our lectronsncovalentonds it htsneighborsormingregularrystalattice.

9 Electronsnhabitingn he alenceand re alledalencelectrons.10 Theireparturereatesolesunoccupiedpace)n he rystalattice.

T

coo.)o

(t,.)oo3

39



n

p-

n

E

an O

n o

ts

P N

1 8

1 9

When he B -E orward ias sremoved,owillal l to ero.l. and . wil l ol low nd all o zerobecausef the everseias f theC- Bunction.

The ollectorurrentanhereforeeturned n or o f f byapply ingrremovinghe orwardias n heB-E erminalsakinghe ransistoro

behaveik e switcn.Figures od show pplicationfatransistors a currentmplifier,l i gh t on t ro l l edw i t ch , hea tcontro l ledwi tch nda soundcontrolledwitchespectively.

20

21

g O

ts

)

o .

a

@ AnalysingLogicGates

A ogicat esan lementaryuildingblock fdigitalircuits.It s anarrangementf electronicswitchesor he mplementationfBooleanogicalculations.Logicatesave ne utputnd neormorenputs.Everyerminalf a logic ate salwaysn oneof the wobinaryconditions:ow 0or alse)rhigh1or rue),epresentedya ow ndhigh oltageespectively.Anassemblyf he ariousogic atecomb ina t i ons nab les the

67

implementationsf complexogic perationseededor heconstructionfcomputersnd ther lectronicystems,Therere ive asicogic ates:AND,R,NOT, ANDndNCR.Theirymbolsnd ruthablesre hownnFigure oe.

lnDUt::AnPnt..,gutput0 0 00 4

I 01 n

U 01

1 1AND gote

A--f---__\I F X

B-l____J

A Input.',.Butput0 0 00 1 1

1 n 4

I

1 1 1ORgote

NAND oote

NO T gote

NOR gote

91 0

Combinot ionof two

logic gotes

A

B

11

12

13

1 4

r,pul4,:,..

ln.Fut':,:,1:':',"fi,ttt,,',',,

0utput,:,],:,,,,,X],,,,:,

0 0 1

0 4I 1

1 0 11 1 0

lnpul. . . .4 ' l , '

Influt.:,1..,...Ell.,,,.

oUtpul.X

n 0,l

I

n 1 01 0 0

1 1 0

A--J---lI p-x

s--I___J

Logicatesan e ombinedor he urposefproducingore omplexunctionsor or he ubstitutionfone ype fgateoranother.Truthablesre ften sedinsteps)owork ut he unctionfacombinationfgates.Figureelowhows simplexamplef he ombinationf wo ogic ates.

tn:put'a ,,lnput

'B G.,Ontgut,Xi . ,=C 'A

0 0 1 00 1 0 01 0 1 1

1 1 0 0

Some pplicationsf ogic atesncontrolystemsncludeafetyystem,treet

lightingsnd ecurityystem.Anexamplefa 2-inputs NDcircuit anbeone hatwould urnon he ireextin-guisherhe n ot hheheat etectornd he mokeensornputsre riggeredsimultaneously.Streetightingsre urnednbya 2-inputsRgate,he nputsfwhich reasignalro m ime lock nd signalrom daylightensor.AcombinationfoneNOT nd wo ND atesora simpleual-switchecuritysystem hownnFigureelow,hich ouldnlockhe oor hen oth witchesare norsound nalarmf hehiddenwitchsno t urnedn.

Switch

B

Switch

(o hiddenswitch)

fi B c ..,:OutpUt...X '. . ,'B

,,,Outpttt..V.,*,At',,B

0 0 1 0 00 I 0 0 0

Only witch son 1 0 1 0 1Both witchesreon 1 1 0 1 l 0

ON ON

41



gHAPTER

KADIOACTIVITY

m UnderstandingheNucleus f an Atom

1 An atoms thesmallestni t f a

chemicallementha thas tsownchemicalroperties.

2 Atoms remade pof fhreemajor

types fsubatomicarticles:roton,

neutronnd lectron.3 Protonsndneutrons,o th re

known s nucleons,ake p hedense, assivetomicucleusn hecentre hile lectronsorm cloud

orbitingrroundhenucleus.4 Electrons ave negativeharge

and re heeast assivef he hree.5 Protons ave positiveharge nd

are bout 836imes oremassivethan lectronshile eutrons,hichhave mass qualo heprotons,

carry ocharge.6. Everyorm f arrangementf the

subatomicart ic lesn an atom scal lednucl ide.

7 Nuclidesfdifferentlementsiffer

in thenumber f thesubatomicparticleshey ontain,articularlyhenumberfprotons.

8 Nuclidesf hesame lementls oexistnmorehan ne orm.

9 They ave hesame umber fprotonsutdiffern thenumberfneutrons.

10 Nuclidesf thesame lement ithdi f ferentumbersf neutronrecalledsotopes.

11 A notation,alledhe tomicymbol,

isdevisedodistinguishne sotopefrom nother.12 Thenumberf protonsnanatom,

A, scalledheatomic umberorprotonumber).

13 The otal umberf profonsndneutronsnanatom, , scalledhenucleonumberormass umber).

14 Hence,henuclidefanelementis epresentedylX .

15 For xample,!ti

andI i

ar e sotopesf heelementithiumLi ):1;

has

protonsnd (=6-3)eutronshile]1 ;ha s protonsnd (=7-3)eutrons.

sp| Analysing adioactive ecay

1 Radioactivityr adioactiveecaysanaturalnd pontaneousrocessywhich

theunstabletoms f anelementisintegratendemit nergeticarticlesrphotonsn he orm f onizingadiations.

2 Such missionouldither ak ehe toms ore tabletastate f owernergy(whileetainingheoriginalorm) r changehenucleusompletelynd husproducedifferentlement.

3 Whenhe ater appens,hedecayingucleusscalledheparentucleusnd

the esultantscalledhedaughterucleus.

4 The mittedarticlesnd he aughterucleusre nownsdecayroducts.5 Threeommonadioactiveecaysrealpha ecay, eta ecay ndgamma

emission.6 Alpha ecaysaprocessnwhich particleithwo eutronsnd wo rotonss

ejectedromhenucleus.7 The articles denticalo henucleusfa heliumto m8 Beta ecaysa processnwhich nelectronsemittedromhenucleus.

I Duringheprocessfemittinglpha rbeta articlehenucleusls oossests

excessnergyyemittingulsesfelectromagneticadiationnd he rocesss

cal ledammamission.10 ExamplesfalphaecayRadium-226)nd eta ecaylodine-131)nd amma

emissionRadium-214)rittenn ormulare s ollowsespectively:

'i2i$,Rr,.+rioq.R*..+..1..tt;,6|:t',.,,,.,t;,!;':,;,'t,. ' ' ' '

..lltll'.1,..'''..*.llfl|'L,,,:",',;,;*"r!';ei""';',:"""L"""'2$Bi+'#Pu-1C;:t

11 The haracteristicsf adioactivemissionsre ummarizedelow.

ChaiacteiiiticS Alphadecay Beta ecay Garn,nrarnisCion

ParticleCharge) Helium+vs1 Electron-ve) Photonno harge)

Symbol !He r cr .feor !B I

Approximateass 4 proton

MASSES-k proton assI o Jo

Nit

lonising ffect Strong Weak Veryweak

Penetratingower 7 cm nair 3mm naluminum 15 m n ead

Shielding aterial Paper,kin,clothes

Plastic,lass,ightmetals

Dense etal,

concrete,arth

Effect f amagneticield

Small eflection Large eflection Noeffect

Speed l l ^ t ^ l -" y ' " 1 0speedf ight

Up of i speedfl igh t

Speedf ight

<)



12

1 3

Commonetectorssedor hedetectionf adioactivityncludeparksounter,Geiger-Mullerube, loudhambers,old-leaflectroscope,cintillationetector(sodiumodide)nd hotographiclates/films.

Figurebelowhowshe chematicfa Geiger-Mullerube ndFigureshowsthe racksf he hreeypes f adiationnacloud hamber.

+

45 0V

Aluminumubecothode

Centrewire

onode

i { ^

S

f

I

I

I

CX,

Thick ndstroight

- \ l) /-+\l)t/

i \//J\ \

J /

(D

BThin nd r regu lo r

b

\ \ \ t , l / t

"\ \ r \ ,

' l ' , ,\ r t l t l l

\ \ , / . '\ \ \ ' /

(D

vI

Shortond scottered

14 Theate f adioactivityecaysunaffectedy he hemicalhangertemperature.15 However,heactivityr heaverageumberfdisintegrationer econdn a

radioactiveecaysalwaysroportionalo he umberf he emaininguclei.16 The alf-lifefa radioactiveaterialanbedefineds he ime equiredor he

materialodecayohalf f ts nitialalue.17 The alf-livesfsomeadioactiveaterialsre x 108 earsorUranium-235,

1620 earsorRadium226, 5hoursorSodium24,52econdsorRadon-220and x 10-7econdsorPolonium-212.

18 Carbon-datingsanapplicationf hehaltlife ropertyf adioactiveaterials.

sf,l Understandinghe Uses f Radioisotopes

lsotopesre uclideshich av ehe ame tomicumberutdifferintheas snumber.Radioisotopesre adioactivesotopes.Someadioisotopesccur atural lyuch slH,

3:U,l !Raand!iRb.Someadioisotopesre rtificiallyroducedyneutronctivation,issionroductseparationrchargedarticleombardment.Examplesfartificiallyroducedadioisotopesre}iio,iiMn,11Nand lll.

The ollowingshow ome f he pplicat ionsf adioisotopesn he ariousields:

234

56

Thinmico .Argongo sot low pressure

Arsaof Application Ra.di6iSol0p,gs AppliCafione

Medicine lodine-131Cobalf60

It .

2.1. usedo reathyroidisorders2. sterilizeurgicalnstruments

Agriculture 1. Phosohorus-322. Selenium-75

1. moleculariologynd eneticsesearch2. proteintudiesn ife cienceesearch

Archaeology 1. Carbon-14 1. datingfarchaeologicalrtifact

lndustry Cesium-137

Throium-230

1 .

2.

1. omeasurehe iquidlownoilpipelines

2. Providesluorescencencoloredlazes

53

@ UnderstandingNuclearEnergy

1 Atomicmassuni t . r a.m.u. ,s

definedobe* of hemass fon eatom f sotop5arbon-1,It is a unitoften sed o express

atomicndmolecularasses.

Themass fcarbon-12s 1.99310'6kgand herefore

i a.m.u.;r'1.661g+r:1n.

Radioactiveecayesultsna ossofmass, hichsconvertedoenergy

accordingo theEinsteinormulaE=mCwhere s energyn oules,

m smassnkilogramsnd is he

square f t hespeed f i gh t nvacuumnms-1= 3x 108ms- l2 .When nucleusissions,tsplitsnto

two rmore malleruclei.In he rocess,wo r hree eutronsarealso mittednd hesum f hemassesf he ragmentss esshanthe riginal ass.About .1Yo f heoriginalassslostandconvertedntoenergyaccordingoEinstein'squation,SinceC in the ormulas relativelylargenvalue, bigamount fenergycanbeobtainedromafractionf hemater ia lhroughheprocessf

nuclearission.A nuclearhaineactionefersoaprocessnwhich eutronseleasedin f iss ion roducen addi t ionalfissionnat east neurtherucleus.Th isnuc leusn tu rnp roduces

neutronsnd heprocessepeats,The rocess ay econtrolleds nnuclearowereactorruncontrolledas nnuciearombs.Figurehowssimplifiediagramfa nuclear eactor here hainreac t i on f nuc lea riss ions

control ledo generatelectr icalenergy.Uranium-235s used s uelandgraphiclocks ith avitieservesthemoderatorcontro lods) ocontrolheneutrons.

10

11

12

13



1 4

1 5

Carbonioxidercold ater cts s

coolanto ransferheheat ut o urn

thegenerator.

Shortagef energyources often

usedo ustifyor heuse fnuclearpower hileisks faccidenthich

will eado ossnhumanives nd

contaminationf environmentre

considerationssed gainstuclearreactor.

Control od drive

Ho tcoolqntto heotexcnongers

Coolont

Cool coolont from heot exchongers

Nuclearusions heprocessywhichmultipleucleiombinefter

col l idingt high peedo form

heavierucleus.Itonly ccursn h eextremelyigh-

energynd emperatureonditions.Nuclearus ion f ight lementsreleasesnergyuch s he rocess

which owershe un ndhe tars.Hydrogenomb xplosionscausedby fus ionof Hydrogen-2ndHydrogen-3ntoHelium-4.

All adioactiveaterialsus there-

fore eclearlyabeledndprecau-

tions uc h swarningigns,ppro-priateui ldingnd ts ocal i tynd

properontainerocontainhema-

terials.Specialehicles,hieldingnd ro-

tectiveears ust eprovidedopro-

tect heenvironmentswell s hepeopleandlinghe ubstance.

lf notmanagedroperly,adioactive

materialsan ontaminateheenvi-

ronmentora on gime nd et nt o

ou rood hain hich illea doseri-

ous icknessesuch seye ataract,

cancernd ellmutation.

Radioactiveastesormallylassi-

f ied s ow-level,edium-levelr

high-levelastes,ccordingo he

amountnd ypes f adioactivityn

them.Three eneralr inciplesreem-ployedn hemanagementf adio-

active astes:(i ) concentrate-and-contain:

thewastesconcentratednd

thensolated:(ii) di lute-and-disperse:

th ewastes dilutedo accepf

ableevelsndhen ischarged

to he nvironment,nd(i i i) elay-and-decay:

thewastesstoredndts adio-activitys allowedo decrease

naturally.Low-levelastesgeneratedrom

hospitals,aboratories,ndustry,nd

the uclearuel ycle.

8 ltcomprisesaper,ags,ools,loth-

ing, i l ters ndetc.which ontain

small mountsfmostlyhort-lived

radioactivity.

9 l t is notdangerouso handle,ut

must edisposedfbyburialnshal-

lo wandfi l li tes.

10 lt s often ompactedr ncinerated

in a closedncineratorefore is -posal.

11 lntermediate-levelaste ontains

higher mountsf radioactivitynd

requirespecialhieldingnhandling.

12 lt ypicallyomprisesesins,hemr-'

ca l ludge,eactoromponentsnd

contaminatedaterialsromeactor

decommissioning.13 lt may esolidifiednconcreterbi-

tumenordisposal.

Generallyhort-livedastemainly

fromeactors)sburied,utong-livedwaste from eprocessinguclear

fuel) il l edisposedfdeep nder-ground.

High-levelastemay e he pent

fuel tself r heprincipalasterom

reprocessinghe uelmaterials.

Itcontainshehighly-radioactiveis-

sion roductsnd ome eavy le-

ments ithong-livedadioactivity,7.

Itgeneratesconsiderablemountf

heat nd equiresoolingswell s

specialhieldinguringandl ingndtransport.Th ewaste houldesealednside

speciallassnd tainlessteelcan-

istersoreventualisposaleep n-

derground.

1 6

1 4

1 5

1 6

1 7

1 8

1 9

sf| ProperManagementof RadioactiveSubstances

1 Radioactiveaterialsamagerde-stroyiving ells nd hereforerehazardousohumaneinq.

1 7

54

Physics Preston Notes

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