Voltage, Current, and Circuits

1ENGI128INTRODUCTIONTOENGINEERINGSYSTEMS

Lecture6:Voltage,Current,andCircuits

UnderstandYourTechnicalWorld

2WelcometoElectricalEngineering!

Wewillstartourstudyofelectricalengineeringwithitstwomostbasicconcepts:voltageandcurrent.

Wellintroducethemostpopularelementinelectricity,theresistor

Wellthenmovetothesimplestpossiblecircuit,thevoltagedivider.

Finally,wellgooversomemeasurementtechniquesthatyouwillneednextweek.

3Voltage&Current

4Well,whatarethey?

Voltage=Electricalpotentialenergy(theabilitytodowork)

Current=Flowofelectricity(workbeingdone)

5Voltagefunfacts: Voltageisthedifference inelectricalpotentialenergy Therefore,voltagemustbemeasuredbetweentwopoints Everysystemhassomereferencevoltagethatwedefineas0.Thisisalsocalledground.

Allothervoltagesaremeasuredrelativetoground

6Currentfunfacts: Currentonlyflowsfromhighvoltagetolowvoltage Currentrequiresavoltage,butnottheotherwayaround Currentcannotleaveacircuit,itmustbeconserved

7[currentandvoltagedemo]

8Howdoyougettheelectronsoffoftheground?

Currentcantflowwithoutawaytogetbackhome Youhavetoaddenergytotheelectronstoincreasetheirvoltage

Thiscreatesacircuit Alltheelectricitywewilllookatandtalkaboutisinacircuit Acircuitisaclosedsystemofelectrons:

Thismeansthatweneverloseanyelectrons Thismeansthatyoucantpushelectronsdownaopenendedwire Thereneedstobeapathtogetbacktohome Ifyouwantthecircuittorunmorethanonce,youneedtogetvoltagebackintotheelectrons

9PowerSupplies

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Wheredowegetvoltageandcurrentfrom?

Batteries

Whatelse?

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Whyallthebatteries?

Butwhydoeseverythingusemorethanonebattery?

a.Tohavemoreenergy

b.Tohavemorevoltage

c.Tohavemorecurrent

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AddingVoltage:Multiplebatteries

Puttingbatteriesinseries:

Puttingbatteriesinparallel:

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Resistors

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Resistors

Resistorsimpedetheflowofcurrent

Sowhyintheworldwouldyoueverusethem? Becauseascurrentflowsthroughthem,itcreatesavoltagedropacrosstheresistor

Thischangeinvoltagecanbeuseful.

Andthisbringsustoouronlyequationinthismodule,Ohmslaw: voltage=current resistance V=IR

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readingresistors:colorcodes

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Schematics

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SchematicSymbols

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ASchematicDiagram:TheVoltageDivider

Singlemostusefulcircuitontheplanet:

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TheVoltageDivider

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[showroneschematicshighlightresistors&voltagedividers]

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VoltageDividerMathOhmsLaw

Conservationofcurrent

Kirchhoffsvoltagelaw

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[showroneschematicsandhighlightvoltagedividers]

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TakingElectricalMeasurements

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TheMultimeter

OK,alltogethernow: Measuringvoltage Measuringresistance

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[multimeter examples]