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Chapter1

ntro uct on

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INTRODUCTIONLesson

Outcome:

tt een o t e esson,stu entss ou ea eto:

Definebasic

concept

of

charge,

current,

voltage,

circuit

elements,powerandenergy.

Calculatethecharge,current,voltage,powerand

energyfor

specific

circuit

elements.

Applyandrelatethebasicconceptaccordingtotheirapplication.

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Cha ter1:Introduction

.

1.2 ElectricCharge.

1.3 urren .1.4 Voltage.

1.5 PowerandEnergy.

1.6 CircuitElements.

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. .The electrical and magnetic units commonly used in electricalcircuit are shown in Table 1.1 and Table 1.2.

Quantity Symbol Unit Symbol

Table 1.1: Electrical quantities

Capacitance

Charge

C

Q

Farad

Coulomb

F

C

Conductance

Current

Energy

G

I

W

Siemens

Ampere

Joule

S

A

J

Frequency

Impedance

f

Z

Hertz

Ohm

Hz

Power

Reactance

P

X

Watt

Ohm

W

Resistance

Voltage

R

V

Ohm

Volt

V

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1.1.ELECTRICAL ANDMAGNETICUNITS(Cont)

Quantity Symbol Unit Symbol

a e . : agnet c quant t es

Flux density

Magnetic flux

B

Tesla

Weber

T

Wb

Magnetizing forceMagnetomotive force

Permeability

HFm

Ampere-turns/meterAmpere-turn

Webers/ampere-turns-meter

At/mAt

Wb/Atm

Reluctance Ampere-turns/weber At/Wb

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1.2ElectricChar es Chargeisanelectricalpropertyoftheatomicparticlesof

whichmatterconsists,measuredincoulombs(C).

Thechargee ononeelectronisnegativeandequalin1

. charge.Thechargesthatoccurinnatureareintegral

multi les ofthe

electronic

char e.

1coulombisaunitofchargethatcontains6.24x1018electrons

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1.3Current 1Electric

Current

is

the

time

rate

of

charge,

measuredinamperes(A).

Mathematicall ,therelationshi betweencurrent

i,charge

q,

and

time

tisi

=dq/dt.

The

unit

of

am erecanbederivedas1A=1C/s.

Adirectcurrent(dc)isacurrentthatremains

Analternatingcurrent(ac)isacurrentthatvaries.

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1.3Current(2)

The

direction

of

current

flow

Positive ions Negative ions

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1.3Current(3)Example1Aconductorhasaconstantcurrentof 5A.

Howman electrons assafixed ointontheconductorinoneminute?

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1.3Current(4)o ut on

Totalno.ofchargespassin1minisgivenby

A= C/s 60s/min = 00C/min

.

minelectrons/1087.1C/electron10602.1

19

xx

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1.4Voltage(1)

chargethroughanelement,measuredinvolts(V).

,

wisenergyinjoules(J)andqischargeincoulomb(C).

ab

Electricvoltage,vab,isalwaysacrossthecircuitelement orbetweentwo

ointsinacircuit.

vab>0meansthepotentialofaishigherthanpotentialof b.

vab