Basic Electrical_Current Voltage Resistance.pdf

Basic electricity

1. Concept of Electric Current
And
Electric Voltage

2. Anelectriccurrentisastreamofchargedparticles,such
aselectronsorions,movingthroughanelectricalconductoror
space.
Electric Current

3. Electriccurrentscreatemagneticfields,whichareusedinmotors,
generators,inductors,andtransformers.Inordinaryconductors,they
causeJouleheating,whichcreateslightinincandescentlightbulbs.
Time-varyingcurrentsemitelectromagneticwaves,whichareused
intelecommunicationstobroadcastinformation.
Effect of Electric Current

4. Electric Voltage or Potential Difference
The Electric Potential is defined asthe amount of work energy needed to move a unit of
electric charge from a reference point to the specific point in an electric field.
Electric Potential

5. Potential Difference
Electric Voltage or Potential Difference
The required amount of energy to move the unit charge from one point to another
is known asVoltage or Potential Difference.
•Onevoltisthedifferenceofelectricpositionalequaltooneampere
ofcurrentdissipatesonewattofpowerbetweentwoconductingpoints.
Or
•Voltisthepotentialdifferencewhichmovesonejouleofenergypercoulomb
chargebetweentwopoints.
V = J/C = W/A …in Volts

6. EMF VsVoltage
WhatisEMF?
EMForElectromotiveForceistheenergysupplytothechargebyabatterycell.
Inotherwords,EMFproducesandmaintainsvoltageinsideanactivecelland
suppliesenergyinjoulestoeachunitofcoulombcharge.Itisrepresentedby“ε”
andthemeasuringunitissameasvoltagei.e.Volt.
EMFisthemaximumpotentialdifferencebetweentwopointsof
thebatterywhennocurrentisflowingfromthesourceincaseofopencircuit.In
short,EMFisthecauseandVoltageorpotentialdifferenceistheeffect.
E or ε = W/Q… in Volts

7. EMF VsVoltage

8. EMF VsVoltage

9. EMF VsVoltage

10. Thank You

11. Resistance
It is defined as the property of a substance due to which it opposes
(or restricts) the flow of electricity (i.e., electrons) through it.
Unitofresistance:
Thepracticalunitofresistanceisohm.A
conductorissaidtohavearesistanceof
oneohmifitpermitsoneamperecurrentto
flowthroughitwhenonevoltisimpressed
acrossitsterminals.
ThesymbolforohmisΩ.

12. Resistance
Symbol

13. Laws of Resistance
The resistance R offered by a conductor depends on the following factors :
(i) It varies directly as its length, l.
(ii) It varies inversely as the cross-section A of the conductor.
(iii) It depends on the nature of the material.
(iv) It also depends on the temperature of the conductor.

14. Resistivity
•Electricalresistivity(alsocalledspecificelectrical
resistanceorvolumeresistivity)isafundamental
propertyofamaterialthatmeasureshowstronglyit
resistselectriccurrent.Alowresistivityindicatesa
materialthatreadilyallowselectriccurrent.
•ResistivityiscommonlyrepresentedbytheGreek
letterρ(rho).
•TheSIunitofelectricalresistivityistheohm-
meter(Ω⋅m).

15. Conductance
Conductance(alsoknownaselectricalconductance)isdefinedasthe
potentialforasubstancetoconductelectricity.Conductanceisthemeasureof
howeasilyelectricalcurrent(i.e.flowofcharge)canpassthroughamaterial.
Conductanceistheinverse(orreciprocal)ofelectricalresistance,represented
as1/R.
ConductanceismeasuredinSiemens(S).

16. Conductivity
Electricalconductivityorspecificconductanceisthereciprocalof
electricalresistivity.Itrepresentsamaterial'sabilitytoconductelectric
current.ItiscommonlysignifiedbytheGreekletterσ(sigma).
TheSIunitofelectricalconductivityissiemenspermetre(S/m).

17. Resistivity and Conductivity of Metal

18. A rectangular carbon block has dimensions 1.0 cm 1.0 cm 50 cm.
(i)What is the resistance measured between the two square ends ?
(ii)between two opposing rectangular faces / Resistivity of carbon at
20°C is 3.5 10
-5
Ohm-m.

19. Thank You

20. Effect of Temperature on Resistance
The effect of rise in temperature is :
(iii)todecreasetheresistanceofelectrolytes,insulators(suchaspaper,rubber,
glass,micaetc.)andpartialconductorssuchascarbon.Hence,insulatorsare
saidtopossessanegativetemperature-coefficientofresistance.
(ii)toincreasetheresistanceofalloys,thoughintheircase,theincreaseis
relativelysmallandirregular.Forsomehigh-resistancealloyslikeEureka(60%
Cuand40%Ni)andmanganin,theincreaseinresistanceisnegligibleovera
considerablerangeoftemperature.
(i)toincreasetheresistanceofpuremetals.Theincreaseislargeandfairly
regularfornormalrangesoftemperature.Thetemperature/resistancegraph
isastraightline.Aswouldbepresentlyclarified,metalshaveapositive
temperatureco-efficientofresistance.

21. Effect of Temperature on Resistance

22. Temperature Coefficient of Resistance
Let a metallic conductor having a resistance of R0 at 0°C be heated of t°Cand
let its resistance at this temperature be Rt. Then, considering normal ranges of
temperature, it is found that the increase in resistance ∆R = Rt -R0 depends
(i) directly on its initial resistance
(ii) directly on the rise in temperature
(iii) on the nature of the material of the conductor
where α(alpha) is a constant and is known as the temperature coefficient of resistance of the
conductor.

23. Temperature Coefficient of Resistance
0

24. Temperature Coefficient of Resistance

25. Value of α at Different Temperatures

26. Value of α at Different Temperatures

27. Thank You

28. Exercise: A copper conductor has its resistance of 16 ohm at 0°C and a resistance
temperature coefficient of 1/254.5 per °C at 20°C.
Find:
(i) the specific resistance and
(ii) the resistance -temperature coefficient at 60°C.