1. The document discusses electricity, including types of charges, units of charge, conductors and insulators, electric potential, potential difference, Ohm's law, resistors, and heating effect of electric current. 2. Key people mentioned include Georg Ohm for whom Ohm's law is named, as well as James Prescott Joule for his experiments relating electrical work to thermal energy. 3. Resistors can be connected in series or parallel, and the document explains how total resistance is calculated for each type of connection.

1. ELECTRICITY
MADE BY
SAIRAM,VIJAYRAKESH,ABHITEJ,RAVITEJA AND AKARSH
X-A

2. Types of charges
• Therearetwotypesofcharges:-
• Positivecharge:-Thesearemadeofsubatomicparticle proton.
• Negativecharge:-Thesearemadeofnegativesubatomic particleelectron.

3. S.I. unit of charge
• TheS.I.unitofchargeis coulomb.
• Anelectronpossesanegative chargeof 1.5x10-19.
• TheS.I.unitofonecoulombisequivalenttothecharge containing6.25x
10-18.

4. Conductors and Insulators
• Thesesubstancehavethe propertyto
conductelectricity throughthem.
• Thesehavefreeorlooselyheld electrons
whichhelpsin conductingelectricity.
• Example–copper.
Conductors Insulators
• Thesesubstancehavetheproperty toobstruct
theflowof electricity.
• Thesedonothavefreeelectrons presentin
them.
• Example–RubberInsulation.

5. Electric potential
• Whenasmallelectricchargeisplacedintheelectricfield duetoanother
charge,itexperiencesaforce.So,workhas tobedoneonthepositivechargeto
moveitagainstthis forceof repulsion.
• Theelectricpotentialisdefinedastheworkdonein movinga unit
positivechargefroinfinitytothatpoint.

6. Potential Difference
• Theconceptofelectricpotentialiscloselylinkedtothatofthe electricfield.Asmall
chargeplacedwithinanelectricfield experiencesaforce,andtohavebroughtthat
chargetothat pointagainsttheforcerequireswork.Theelectricpotentialat any
pointisdefinedastheenergyrequiredtobringaunittest chargefromaninfinite
distanceslowlytothat point.
• Itisusuallymeasuredinvolts,andonevoltisthepotential forwhichonejouleof
workmustbeexpendedtobringa chargeofonecoulombfrominfinity.

7. 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒
Potentialdifference= 𝑄 𝑢 𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐ℎ𝑎𝑟𝑔𝑒 𝑚 𝑜 𝑣 𝑒 𝑑
.
𝑊
or, V= 𝑄
.
whereW=workdone.
andQ =quantityofchargemoved.
1 𝑗𝑜𝑢𝑙 𝑒
S.I.unitofpotentialdifferenceisvolt. thus1volt=
1 𝑐𝑜𝑢𝑙𝑜𝑚𝑏

8. Voltmeter
• Avoltmeterisaninstrument usedfor
measuringelectrical potentialdifference
between twopointsinanelectric
circuit.
• Voltmeterhasahigh resistanceso
thatittakes negligiblecurrent.

9. Electric Current
• Themovementofelectricchargeisknownasanelectric current,the
intensityofwhichisusually measured
inamperes.Currentcanconsistofanymovingcharged
particles;mostcommonlytheseareelectrons,butany chargeinmotion
constitutesacurrent.
1𝑆𝑒𝑐𝑜𝑛𝑑
• 1ampere= 1 𝐶𝑜𝑢𝑙𝑜𝑚𝑏
.

10. Ammeter
• Anammeterisameasuring instrument
usedtomeasure theelectriccurrentina
circuit.
Electriccurrentsaremeasured inamperes
(A),hencethename.
• Anammetershouldhaveavery low
resistancesothatitmaynot changethe
valueofcurrent flowinginthe circuit.

11. Circuit Diagram
• Weknowthatanelectriccircuit,asshowninFig.12.1, comprisesacell(ora
battery),aplugkey,electrical component(s),andconnectingwires.Itisoften
convenientto drawaschematicdiagram,inwhichdifferentcomponentsof the
circuitarerepresentedbythesymbolsconvenientlyused. Conventionalsymbols
usedtorepresentsomeofthemost commonlyusedelectricalcomponents.

13. Georg Ohm
• GeorgSimonOhm(16March1789–6 July1854)wasa
Germanphysicistand mathematician.Asaschool
teacher,Ohmbeganhisresearchwiththe
newelectrochemicalcell,inventedby Italianscientist
AlessandroVolta.Using equipmentofhisowncreation,
Ohmfoundthatthereisadirectproportionality between
thepotentialdifference(voltage) appliedacrossa
conductorandthe resultantelectriccurrent.This
relationshipisknownasOhm'slaw.

14. Ohm’s Law
• Ohm’sLawexplainstherelationshipbetweenvoltage(V orE),current(I)and
resistance(R)
• Usedbyelectricians,automotivetechnicians,stereo installers.
• AccordingtoOhm’slaw:Atconstanttemperature,the currentflowing
throughaconductorisdirectly proportionaltothepotentialdifference
acrossitsend.

15. 𝑉
• AccordingtoOhm’slaw:
V∝I
or, V= RxI.
whereRisconstant“resistance”oftheconductor.
Thiscanalsobewrittenas –
or, I= 𝑅
.
𝑉
So, Current, I= 𝑅
.
Therefore,
i. Thecurrentisdirectlyproportionaltopotential difference.
ii. Thecurrentisinverselyproportionalto resistance.

16. Resistance
• Anelectrontravelingthroughthewiresandloadsofthe externalcircuitencounters
resistance.Resistanceisthe hindrancetotheflowofcharge.Foranelectron,the
journey fromterminaltoterminalisnotadirectroute.Rather,itisa zigzagpaththat
resultsfromcountlesscollisionswithfixed atomswithintheconductingmaterial.
Theelectronsencounter resistance-ahindrancetotheir movement.
• TheS.I.unitofresistanceisohm’s(Ω).

17. Factors affecting Resistance
i. Lengthofconductor.
ii. Areaofcrosssectionoftheconductor(orthicknessof theconductor).
iii. Natureofthematerialoftheconductor, and
iv. Temperatureofconductor.

18. Resistivity
• Ithasbeenfoundbyexperimentsthat:
• Theresistivityofagivenofagivenconductorisdirectlyproportional toits length.
R∝ l ……………..(1)
𝑙
• Theresistivityofagivenconductorisinverselyproportionaltoits areaofcross section.
R∝ 1/A ……………(2) Combining(1)and
(2),weget :
R∝l/A
R=𝑝× 𝐴
………………….(3)

19. • Wherep(rho)isaconstantknownasresistivityofthematerial.
• Theresistivityofasubstanceisnumericallyequaltotheresistanceof arodofthatsubstance
whichis1meterlongand1squaremeterin crosssection.
𝑙
• Resistivity, p= 𝑅 𝑥 𝐴
.
• TheunitofresistanceRis ohm.
• Theunitofareaofcross-sectionAis(meter)2.
• Theunitoflengthlis meter.
puttingtheseunitintheaboveequation–
p=
𝑜 ℎ 𝑚 × 𝑚𝑒𝑡𝑒𝑟 2
𝑚𝑒𝑡𝑒𝑟
.
p=ohm-meter.
TheS.I.unitofresistivityisohm-meter(Ωm)

20. Resistivity of some common substances (200 C )

21. • Theresistivityofalloysaremuchmorethanthoseofpure metals(fromwhich
theyaremade).
• Forexampletheresistivityofmaganine(whichisan alloyofcopper,
manganeseandnickel)isabout25times morethanthatofcopper.
• Alloysareusedinmakingheatingamaterialsas –
i. Alloyshaveveryhighresistivity(duetowhichheating elementsproducea
lotofheatonpassingcurrent).
ii. Alloysdonotundergooxidationeasilyevenathigh temprature.

22. Combination of Resistors
• Resistorscanbecombinedintwoways –
i. Inseries.
ii.Inparallel.

23. Resistors in Series
• Whentwo(ormore)resistorsareconnectedendtoend consecutively,they
aresaidtobeconnectedinseries.
• Accordingtothelawofcombinationofresistancein series:Thecombined
resistanceofanynumberof resistancesconnectedinseriesisequalto
thesumof theindividual resistances.
R=R1+R2+R3+………..

24. I. Whenanumberofresistorsconnectedinseriesare joinedtotheterminalofa
battery,theneachresistance hasadifferentpotentialdifferenceacrossitsends
(whichdependsonthevalueofresistance).Butthetotal potentialdifference
acrossalltheendsofalltheresistors inseriesis equal.
II. Whenanumberofresistorsareconnectedinseries,then thesamecurrent
flowsthrougheach resistance.

25. Resultant of Resistances connected in Series
• Resultant of Resistances connected in
• Series
• • The figure shows three resistances R1,R2,R3 connected in series. Now suppose
• potential difference across resistance R1 is V1 , R2 is V2 and R3 is V3. Let
• potential difference across battery be V, then :
• V = V1+V2+V3.
• Applying Ohm’s law to the whole circuit : V = IR. ………..(1)
• Applying Ohm’s law to the three resistors separately, we get:
• V1 = I x R1. ………………….. (2)
• V2 = I x R2. ………………….. (3)
• V3 = I x R3. ………………….. (4)
• Substituting (2), (3), (4) in (1)
• IR = IR1 + IR2+ IR3
• OR, IR= I (R1+R2+R3)
• Or, R = R1+R2+R3 .
• Therefore we conclude that the sum total resistance in a series resistance
• connection is equal to the sum of all the resistances.

26. Resistors in Parallel
• Whentwo(ormore)resistorsareconnectedbetweenthesame points,theyaresaidto
beconnectedin parallel.
• Accordingtothelawofcombinationofresistanceinparallel: Thereciprocalofthe
combinedresistanceofanynumber ofresistancesconnectedinparallelisequal
tothesumof thereciprocalsoftheindividualresistances.
1/R=1/R1+1/R2+1/R3+………..
• When a number of resistances are connected in parallel then their combined
resistanceislessthanthesmallestindividual resistance.

27. • Whenanumberofresistanceareconnectedinparallel,thenthe potentialdifference
acrosseachresistanceissamewhichisequal tothevoltageofbattery applied.
• Whenanumberofresistancesconnectedinparallelarejoinedto thetwoterminalsofa
battery,thendifferentamountsofcurrent flowthrougheachresistance(whichdependon
thevalueof resistance).Butthecurrentflowingthrougheachparallel resistance,taken
together,isequaltothecurrentflowinginthe circuitasawhole.Thus,whenanumberof
resistanceare connectedinparallel,thenthesumofcurrentflowingthroughall the
resistancesisequaltothetotalcurrentflowinginthecircuit.

28. Resultant of Resistances connected in
Parallel
• Resultant of Resistances connected in
• Parallel
• • The figure shows three resistances R1,R2,R3 connected in series. Now suppose
• currant across resistance R1 is I1 , R2 is I2 and R3 is I3. Let total current in the
• circuit be I, then:
• I = I1+I2+I3.
• Applying Ohm’s law to the whole circuit : I = V/R. ………..(1)
• Applying Ohm’s law to the three resistors separately, we get:
• I1 = V / R1. ………………….. (2)
• I2 = V / R2. ………………….. (3)
• I3 = V / R3. ………………….. (4)
• Substituting (2), (3), (4) in (1)
• V/R = V/R1 + V/R2+ V/R3
• OR, V/R= I (1/R1 +1/R2 + 1/R3)
• Or, 1/R = 1/R1+1/R2+1/R3 .
• Therefore we conclude that the sum total resistance in a parallel resistance
• connection is equal to the sum of reciprocal of all the resistances.

29. Parallel and Series connection
• Ifoneelectricappliancestopsworkingdue tosomedefect,
thenallotherappliances keepworkingnormally.
• Inparallelcircuits,eachelectricappliance hasitsown
switchduetowhichitcanbe turnedonoroff
independently.
• Eachappliancegetssamevoltageasthat
ofpowersource.
• Overallresistanceofhouseholdcircuitis reduceddueto
whichthecurrentfrom powersupplyis high.
Parallelconnection Seriesconnection
• Ifoneelectricappliancestopworkingdue tosomedefect,
thenallotherappliances stopworking.
• Alltheelectricapplianceshaveonlyone switchdueto
whichtheycannotbeturned onoroff separately.
• In series circuit, the appliances do not get same voltage
(220V)asthatofthepower supplyline.
• Inseriescircuittheoverallresistanceof thecircuit
increasesduetowhichthe currentfromthepower
sourceis low.

30. Heating effect of electric current
• Whenelectricitypassesthroughahighresistancewirelike anichromewire,the
resistancewirebecomesveryhotand producesheat.Thisis calledtheheating
effectofcurrent.

31. James Prescott Joule
JamesPrescottJoule(24December1818–11October 1889)wasanEnglish
physicistandbrewer,borninSalford, Lancashire.Joulestudiedthenatureof
heat,anddiscovered itsrelationshiptomechanicalwork.Thisledtothelawof
conservationofenergy,andthisledtothedevelopmentof thefirstlawof
thermodynamics.TheSIderivedunitof energy,thejoule,isnamedforJames
Joule.Heworked withLordKelvintodeveloptheabsolutescale
oftemperature.Joulealsomadeobservationsof magnetostriction,andhefound
therelationshipbetweenthe currentthrougharesistorandtheheatdissipated,
whichis nowcalledJoule'sfirstlaw.

32. Joule’s law of heating
Let
AnelectriccurrentIisflowingthrougharesistorhavingresistanceequaltoR. Thepotentialdifference
throughtheresistorisequalto V.
ThechargeQflowsthroughthecircuitforthetime t.
Thus,workdoneinmovingofchargeQofpotentialdifferenceV=VQSince,thischargeQflows
throughthecircuitfortimet,

33. • Theheatproducedinwireisdirectlyproportionalto
i. Squareofcurrent.
ii. Resistanceof wire.
iii. Timeforwhichcurrentispassed.

34. Applications of heating effect of electric
current
Therearemanypracticalusesofheatingeffectofcurrent.Someofthemostcommonareas follows.
• Anincandescentlightbulbglowswhenthefilamentisheatedbyheatingeffectofcurrent,sohot
thatitglowswhitewiththermalradiation(alsocalledblackbodyradiation).
• Electricstovesandotherelectricheatersusuallyworkbyheatingeffectofcurrent.
• Solderingironsandcartridgeheatersareveryoftenheatedbyheatingeffectofcurrent.
• Electricfusesrelyonthefactthatifenoughcurrentflows,enoughheatwillbegeneratedtomelt thefusewire.
• Electroniccigarettesusuallyworkbyheatingeffectofcurrent,vaporizingpropyleneglycoland
vegetableglycerin.
• Thermistorsandresistancethermometersareresistorswhoseresistancechangeswhenthe temperaturechanges.Thesearesometimes
usedinconjunctionwithheatingeffectofcurrent(also calledself-heatinginthiscontext):Ifalargecurrentisrunningthroughthe
nonlinearresistor,the resistor'stemperaturerisesandthereforeitsresistancechanges.Therefore,thesecomponentscanbe usedina
circuit-protectionrolesimilartofuses,orforfeedbackincircuits,orformanyother purposes.Ingeneral,self-heatingcanturnaresistor
intoanonlinearandhystereticcircuitelement.

35. Electric Energy
• H=I2 Rtgivestherateatwhichelectricenergyisdissipatedorconsumedinanelectric
circuit.Thisisalsotermedaselectricpower.ThepowerPisgivenby
P=VI
OrP=I2R= V2/R
• TheSIunitofelectricpoweriswatt(W).Itisthepowerconsumedbyadevicethatcarries1 Aofcurrentwhenoperatedata
potentialdifferenceof1V. Thus,
1W=1volt×1ampere=1VA
• Theunit‘watt’isverysmall.Therefore,inactualpracticeweuseamuchlargerunitcalled ‘kilowatt’.Itisequalto1000watts.
Sinceelectricalenergyistheproductofpowerandtime, theunitofelectricenergyis,therefore,watthour(Wh).Onewatthour
istheenergy consumedwhen1wattofpowerisusedfor1hour.Thecommercialunitofelectricenergyis kilowatthour(kW
h),commonlyknownas‘unit’.
1kWh=1000watt×3600second
= 3.6× 106wattsecond
= 3.6× 106joule(J)

36. PPT MADE BY
BHADRACHALAM PUBLIC
SCHOOL