realphysicslab7

realphysicslab7 - Lab7:Voltage,Current,and ResistanceI...

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Unformatted text preview: Lab7:Voltage,Current,and ResistanceI StaciWilliams NicoleHarty,KevinSchesing,CaitlingKubota Section015 Theory: Voltage Twopointshaveavoltagebetweenthemifworkisdonebytheelectricfieldasa chargeismovedfromoneofthepointstoanother.Voltageistheworkdoneona unitpositivechargebytheelectricfieldastheunitpositivechargeismovedfrom oneofthetwopointstotheotherpoint,withunitsofjoulespercoulomb,orvolt. Wireshaveresistanceandarecarryingcurrents,andthewireisnotat equipotential.Theearthisnotagoodconductor.Voltagecanbesuppliedby batteries,powersupplies,andsignalgenerators.Idealvoltagesourcesmaintainsthe prescribedvoltageacrosstheterminalsnomatterhowmuchcurrentissupplied, butthesedonotexist.Voltagecanbeseenasafunctionoftimeandthevoltage acrosstheterminalsofasignalgeneratormayrepeatitselfinalengthoftimecalled theperiod.Thevoltageforoneperiodiscalledoneoscillationoronecycle.The inverseoftheperiodisfrequency,whichisthenumberofperiodsoroscillationsper second.Theshapeofthevoltagevs.timegraphiscalledthewaveform,whichmay varyinshapessuchassine,square,triangular,andramp.Voltagecanbemeasured byavoltmeter,whichhastwoleadsgivingthevoltagedifferencebetweenthetwo leads,drawingfromthecurrent. Current Currentisthechargesmovinginspaceofconductingmaterialswhichistheamount ofchargethatpassesapointinawireinunittime,measuredincoulombsper second,oramperes.Currentismeasurebybreakingthewireandconnectingthe twowireendstoanammeter,withthecurrentpassingthroughtheammeter.The internalresistanceoftheammetershouldbelowenoughsothatthereturned currentisnotloweredbymuch.ACcurrentscanbemeasuredbytheclampon ammeterwithoutbreakingthecurrent.Currentsuppliestrytodeliverthe prescribedcurrentnomatterwhatvoltageappearsacrosstheterminals ResistorsandOhmsLaw Inaconductortherearemobilechargesthatcanmoveifthereisanelectricfield, causingthecurrenttoflow.Theelectricfieldissuppliedbychargestathavebeen providedbyavoltageoracurrentsourceandthesechargesresideonoppositesides oftheconductor.Theforceoftheelectricfieldonthemobilechargesisopposedby frictionalforcesthatresultfromthecollisionsofthemobilechargeswithionsinthe latticeoftheconductor.Adevicethatpurposelyimpedesthecurrentisaresistor, andthevoltageacrossaresistoristhevoltagebetweenanytwopointsthatarethe endsoftheresistor.IfVisthevoltageacrossaresistorandIisthecurrentthrough theresistorthenV=IRThisisagreatapproximation,butnotalways accurate.ThepowerdissipatedinaresistorisgivenbyVI,andinanohmicresistor thepowerdissipatedcanbewrittenasI^2RorV^2/R. ResistorsinSeriesandParallel Iftworesistorsareconnectedinseriesthecombinationisequivalenttoasingle resistorRbyReq=R1+R2Iftworesistorsareconnectedinparallelitis givenby1/Req=1/R1+1/R2. Data/Calculations/Questions/Information: 7.Whenthefrequencyisdecreasedtheoutputvoltagedecreasesandwhenthe ampsaredecreased,theoutputvoltageincreases. Whenanampvalueistypedoutsideoftherangethereisnochange.Whenthe frequencyvalueisoutsideoftherangetheoutputrateincreases. Themeterreadingis25DCvolts,anditisfivetimesmorethantheprogrammed volts.WhentheMONisstillactiveitisunabletochangetheDCvoltagetoanother. Whenthefrequencyischangedto0.2Hz,5VAC,andpositiveonlyupramp 5V 0 Themeterreadingissteadyat2.5Vforthisrecording,andtheoutputvoltage increasesfrom0Vto5V,thenjumpsto0Vandrepeats.Ifthevoltmetercenterwas not0,a100Hzsinusoidalvoltagewouldregisterbecausethemaximumrangeofthe voltmeteris+/12.5V. 8. Theoutputinthedisplayreads5.007,thevoltmeterreads25V,andthe programmedvalueis5.00. Thecurrentonthe5Vscaleis.000977A,andonthe25Vscaleitis.000214. Theinternalresistanceonthe25Vscaleis116822ohms,andforthe5Vscaleis 5118ohms. 10. For100ohmresistortherangofacceptableresistanceis80120ohms.Forthe150 ohmresistortherangeofacceptableresistanceis120ohmsto180ohms. t 11. Theresistoriswarm. Measuredvoltage/current 5.007V/.051=98.2ohms 3.001/.030=100.2ohms 1.006/.010=100.6ohms Thetrendisthatresistanceofslighttendtoincreasewithdecreasingvoltage. 12. ThesearewaveformsofACcurrents. ErrorAnalysis: Theonlymeasurementwithknowntruevaluesaretheoutputvoltagesandthereis littleexperimentercontroloverit,soanyerrorcanbeattributedtothatand possibleslighthumanerrors. Conclusions: IftwoofthethreenecessarycomponentsofOhmslawareknown,thethirdiseasy tocalculate.Whilegraphingoutputsallgraphswillallhavethesamemaximumand minimumvoltages. ...
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