8/3/2019 00 Introduction 2 [Compatibility Mode]

1/5

INTR

ODUCTION

INTR

ODUCTION

INTR

ODUCTION

INTR

ODUCTION

MC

B1033EPM

MC

B1033EPM

MC

B1033EPM

MC

B1033EPM

RosmawatiMatZain

RosmawatiMatZain

RosmawatiMatZain

RosmawatiMatZain

MechanicalEngineeringDepartment

UniversitiTeknologiPETRONAS

18-03-19

05-3687147

rosmaw

ati@petronas.com.my

ElectricalCircuitConcepts

ElectricalCircuitConcepts

ElectricalCircuitConcepts

ElectricalCircuitConcepts

WhatisVoltageandCurre

nt?

WhatisVoltageandCurre

nt?

WhatisVoltageandCurre

nt?

WhatisVoltageandCurre

nt?

Voltage,

Voltage,

Voltage,

Voltage,

VVVV

Voltage

Voltage

Voltage

Voltage

Everysourceof

voltageisestablishedbysimply

Everysourceofvoltageisestablishedbysimply

Everysourceof

voltageisestablishedbysimply

Everysourceofvoltageisestablishedbysimply

creatinga

creatinga

creatinga

creatingasepa

ration

sepa

ration

sepa

ration

sepa

rationofpositiveandnegative

ofpositiveandnegative

ofpositiveandnegative

ofpositiveandnegative

Charges

Charges

Charges

Charges

Stilld

onotunderstand?

Stilld

onotunderstand?

Stilld

onotunderstand?

Stilld

onotunderstand?

Voltag

e,

Voltag

e,

Voltag

e,

Voltag

e,

VVVV

Voltage

Voltage

Voltage

Voltage

The

differenceinenergylevelofaunit

charge

The

differenceinenergylevelofaunit

charge

The

differenceinenergylevelofaunit

charge

The

differenceinenergylevelofaunit

charge

loc

atedateachoftwopointsinacircuit,and

loc

atedateachoftwopointsinacircu

it,and

loc

atedateachoftwopointsinacircuit,and

loc

atedateachoftwopointsinacircu

it,and

therefore,representsthe

therefore,representsthe

therefore,representsthe

therefore,representstheenergyrequiredtomove

energyrequiredtomove

energyrequiredtomove

energyrequiredtomove

th

eunitcharge

th

eunitcharge

th

eunitcharge

th

eunitchargefromonepointtothe

other

fromonepointtothe

other

fromonepointtothe

other

fromonepointtothe

other

8/3/2019 00 Introduction 2 [Compatibility Mode]

2/5

Closeyoureye

s..

Closeyoureye

s..

Closeyoureye

s..

Closeyoureye

s..

Imaginewaterflowfromareservoir

a b

vab

=v

oltagedrop

vba

=v

oltagerise

Voltage

(potentialdifference)

Theene

rgyrequiredtomoveaunitcharge

throughan

element,measuredinvolts,V

vab

=-

vba

dq

dw

vab

=

Electr

icalCircuitConcepts

Howdoweme

asureVoltage?

Howdoweme

asureVoltage?

Howdoweme

asureVoltage?

Howdoweme

asureVoltage?

Current

Timera

teofchangeofcharge,measured

inAmpere.

Timera

teofflowofelectricchargepastagivenpoint.

=

=

tt

idt

q

dt

dq

i

0

Curre

nt,I

+

+

_

_

Thesign

ofthecurrent

indicates

thedirectionofflow

8/3/2019 00 Introduction 2 [Compatibility Mode]

3/5

Typesofcurrent:

directcurrent

directcurrent

directcurrent

directcurrent(dc):

(dc):

(dc):

(dc):current

re

mainconstantwithtime.

e.g.batteriesand

somespecial

generators

alternatingcurrent

alternatingcurrent

alternatingcurrent

alternatingcurrent(ac):

(ac):

(ac):

(ac):currentthat

variessinusoidallywithtime.

e.g.householdcurrentwhichvaries

withtime

Current,I

Current,I

Current,I

Current,I

Exampleofcurrent

Exampleofcurrent

Exampleofcurrent

Exampleofcurrent

Howdoweme

asureCurrent?

Howdoweme

asureCurrent?

Howdoweme

asureCurrent?

Howdoweme

asureCurrent?

ElectricalCircuitConcepts

ElectricalCircuitConcepts

ElectricalCircuitConcepts

ElectricalCircuitConcepts

VoltageandCurrent?

VoltageandCurrent?

VoltageandCurrent?

VoltageandCurrent?

Whichcamefirst?

Whichcamefirst?

Whichcamefirst?

Whichcamefirst?

Chicken

Chicken

Chicken

Chicken

Egg

EggEgg

Egg

8/3/2019 00 Introduction 2 [Compatibility Mode]

4/5

VoltageorCurrent?

VoltageorCurrent?

VoltageorCurrent?

VoltageorCurrent?

TheAppliedvoltage

isthestartingmechanism

TheAppliedvoltage

isthestartingmechanism

TheAppliedvoltage

isthestartingmechanism

TheAppliedvoltage

isthestartingmechanism

thethethethe

current

current

current

currentisaisaisaisarea

ction

rea

ction

rea

ction

rea

ctiontotheapplied

voltage

totheapplied

voltage

totheapplied

voltage

totheapplied

voltage

Theappliedvoltage

(PotentialDifference)inane

lec

Theappliedvoltage

(PotentialDifference)inane

lec

Theappliedvoltage

(PotentialDifference)inane

lec

Theappliedvoltage

(PotentialDifference)inane

lec

tricalsystemisthePressuretosetthesystem

in

tricalsystemisthePressuretosetthesystem

in

tricalsystemisthePressuretosetthesystem

in

tricalsystemisthePressuretosetthesystem

in

motion,andthec

urrentisthereactiontothatpres

motion,andthec

urrentisthereactiontothatpres

motion,andthec

urrentisthereactiontothatpres

motion,andthec

urrentisthereactiontothatpres

sure.

sure.

sure.

sure.

Active

vs.PassiveElements

Activeelementscangeneratee

nergy:

Batteries

Voltageandcurrentsources

Passiveelementscannotgenerateenergy:

Res

istors

Cap

acitorsandInductors(butCANsto

reenergy)

Power

Timerateofexpandingor

absorbingenergy,measured

inwatts,W.

[1]

vi

dt

dq

dq

dw

dt

dw

p

=

=

=

.

ElectricalCirc

uitConcepts

Energy

Thecapacitytodowo

rk,

measuredinjoules(J)

[1]

SignC

onvention

Passive

signconvention:currentente

rsthrough

thepositivepolarityofthevoltage

ConsequenceforP=VI

Positiv

e(+)Power:elementabsorbspow

er,P=vi

Negative(-)Power:elementsuppliespow

er,P=-vi

Lawofconservationofenergy:

CircuitElement

+

I

0

=

=

+

p

or

supplied

,

Power

-

absorbed

Power

8/3/2019 00 Introduction 2 [Compatibility Mode]

5/5

BasicElectricalQuantities

Basicquantities:

current,voltageandpower

Current:time

rateofchangeofelectriccharge

I=dq/dt

1Am

p=1Coulomb/sec

Voltage:electromotiveforceorpotential,V

1Volt=1Jou

le/Coulomb=1Nm/coulomb

Power:

P=IV

1Watt=1Vo

ltAmp=1Joule/sec