Lab 8 - Magnetic Fields - Physics charges produce electric fields. ... “Tesla” is a large unit with one Tesla being a very strong magnetic field. ... Lab 8 - Magnetic

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<ul><li><p>Lab8:MagneticFields</p><p>Name:</p><p>GroupMembers:</p><p>Date:</p><p>TAsName:</p><p>Objectives:Tomeasureandunderstandthemagneticfieldofabarmagnet.Tomeasureandunderstandthemagneticfieldofanelectromagnet,inparticular,asolenoid.Apparatus:Barmagnetbox,compass,PASCOmagneticfieldsensor,USBwire,PASCOinterface,multimeter,powersupply,redandblackleadsandalligatorclips,rheostat. Electricchargesproduceelectricfields.Magnetsandelectromagnetsproducemagneticfields. Weusedtheelectricfieldmodeltoexplainhowachargeorachargedistributionexertsforcesonotherchargesatadistance. Similarlyweuse themagnetic fieldmodel toexplainhowamagnetexerts forcesonothermagnetsandchargesmovingrelativetothefield.Thereforemagneticfieldisavectorquantity.Magneticfield ismeasured inTesla(T). Tesla isa largeunitwithoneTeslabeingaverystrongmagnetic field.Small magnetic fields like the magnetic field of a small bar magnet are measured in millitesla. Thehorizontalcomponentoftheearthmagneticfieldisabout50microteslaonthesurfaceoftheearth.Welearnedthatpositiveandnegativeelectricchargescanbeseparatedandmonopolesanddipolesoccurnaturally.However, inmagnetsweonlyfindmagneticdipolesinnaturewherewealwaysfindanorthpoleandsouthpoletogether.Hereinthisexperimentwequalitativelyinvestigatethemagneticfieldaroundabarmagnet(permanentmagnet)andanelectromagnetusinga tiny testmagnetcalleda compass. Thenwewillmeasure themagneticfieldofabarmagnetandanelectromagnetusingPASCOmagneticfieldsensorandstudyhowthemagneticfielddependsonposition,current,etc.PartA:PermanentMagnets</p><p>1. Takethetwobarmagnetsoutoftheboxandinvestigatetheirinteraction.Explainhowthepolesinteractintermsofattractionandrepulsion.</p></li><li><p>2. Now place one magnet on the marked space below and identify north and south poles of themagnet.Thedirectionofthemagneticfieldatapointinspaceisindicatedbythecompassmagnet.Thenusing the compass identify the direction of themagnetic field at the points shown. Thendrawmagneticfieldlinesconnectingappropriatepointstocreateamagneticfieldlinedrawing.</p><p>3. NowconnectthePASCOmagneticfieldsensortothePASCOpassportinterfaceandtheinterfacetothecomputerviaUSBcable.OpenuptheCAPSTONEsoftwareandselectthegraphandmeterwindow.Selecttheverticalaxistobemagneticfieldandthehorizontalaxistobetime.Changethesamplingrateto10samplespersecond.Presstherecordbuttonandseeifitrecordsdataonthe graph. Move the sensor away frommagnets and see if the value changes fromposition topositionandinwhichdirectionthesensorisdirected.Enlargethescaleofthemagneticfieldaxistoreadthevalueinminitesla.(1mT=0.001T).</p><p>Alignthesensorasfollowstomeasurethemagneticfield.DirectionofthemagneticfieldWhenyoualignthesensorasshownReadingispositive.</p><p>Thesensorhastobeperfectlyalignedwiththemagneticfieldtomeasureitaccurately.Makesurethatyoukeepthesensorasshowninthefigure.</p></li><li><p>4. Keepthemagneticfieldsensorasshownbelowandmeasurethemagneticfieldattheedgeofthemagnet.Itmaybehelpfultoputsomethingunderthemagnetsothatthemagnetandsensorareatthesameheight.Thenmovethesensoralongtheaxisofthemagnettotherightandmeasurethemagneticfieldatfivedifferentpoints.Keepthesensoratafixedpositionandruntheprogramtoseethereadingasafunctionoftime.Gettheaveragereadingandrecorditbelow.</p><p>Magnet Sensor</p><p> SN</p><p>Position(cm) Magneticfieldstrength(mT)0.1 0.5 1.0 1.5 2.0 2.5 </p><p>5. TransferdatatoanExcelfileandplotmagneticfieldvs.position.Drawanappropriatetrendline</p><p>anddisplaytheequationonthechart.Namethegraph,labelaxes,anddisplayunits.</p><p>6. Qualitativelyexplainhowthestrengthofthemagneticfieldchangeswithdistancefromtheedgeofthemagnetbasedonyourgraph.</p><p>7. Yourdatamightindicateamagneticfieldevenwhenthesensorisfarawayfromthemagnet.Whatarethepossiblereasonsforthissituation?(Slowlymovetheprobearoundotherwires,computersetc.andseeiftheyindicateanymagneticfield)</p></li><li><p>PartB:Electromagnets</p><p>The figure below shows a schematic diagram of a solenoid. The direction of themagnetic fieldcreatedbythesolenoiddependsonhowthewireiswrappedandthedirectionofthecurrentflow(whichend itenters).Thestrengthof themagnetic fielddependson thenumber turnsperunitlengthofthesolenoid,thecurrentinthewire,andthemagneticpermeabilityinthemedium.</p><p>magneticfieldNScurrentincurrentout</p><p>Youaregivenasolenoidanditisanelectromagnet.Carefullyobservehowitismade.Aninsulatedwire iswrappedaroundahollowmetallic cylinder.Whena current flows through thewire thesolenoidbecomesanelectromagnet. In thisexperimentyouwant to investigate thestrengthofthemagneticfieldinsidethesolenoidasthecurrentisvaried.Weneedtosendaknowncurrentthroughthesolenoidwireandmeasuremagneticfield.Connectthecircuitasshownbelowfortheexperiment.</p><p> SensorInterfacecomputerSolenoidPowersupplyAmmeter Rheostat(variableresistor)</p><p>8. Powersupplyissetaround5.0Vforyouandadjusttherheostatuntilthecurrentindicatedbytheammeteris0.25A.Placethemagneticsensorasshownaboveandmakesurethatalignswiththeaxisofthesolenoid.Inserttheprobeaboutoneinchintothesolenoidandreadthemeasurement.Withtrialanderrorfindoutthemaximumreadingforrecording.Recordthereadingbelowwithunits.</p><p>Magneticfield=__________________________________</p><p>9. Switchoffthepowersupply.Thenswitchthedirectionofthecurrentbyswitchingthewires</p><p>connectedtothepowersupply.Switchonthepowersupply.Recordthereadingbelowwithunits.Makesurethecurrentisstill0.25A.</p><p>Magneticfield=__________________________________</p></li><li><p>10. Whydoesthemagneticfieldhaveadifferentsignnow?Explain.</p><p>11. Now repeat the same measurement as in Question #8 with a range of values for the currentflowingthroughthewiresofthesolenoid.Recordyourdatainthetable.</p><p>Current(A) Magneticfield(mT)0.25 0.50 1.25 1.50 1.75 2.00 </p><p> Themagneticfieldinsideasolenoidisexpectedtobegivenbytheequation</p><p> = !!!"!</p><p>= !</p><p> where = !!= !"#$%&amp; !" !"#$%</p><p>!"#$%!, ! = 1.257106 Tm/A </p><p>So this suggests that themagnetic field is linearlydependenton thecurrent. Plot themagneticfieldvs.currentgraphinExcel.Drawalineartrendlineanddisplayequationonchart.</p><p>12. Are your measurements of magnetic field vs. current consistent with a linear relationship?Explainwhyyoucometothatconclusion.</p><p>13. Usetheslopeofyour linear fitting todeterminethenumberof turnsperunit length,, for thissolenoid.Showyourwork.RemembertowatchexponentssinceyoumeasuredthefieldinmT. =____________________________</p></li><li><p>PartC:ConclusionsandReflection</p><p>14. Summarizewhatyoulearnedaboutthemagneticfieldfromabarmagnet.</p><p>15. Summarizewhatyoulearnedaboutthemagneticfieldfromasolenoid.</p><p>16. Wedidnotconsidertheeffectofearthsmagneticfieldwhendoingourexperiment.Wouldyourresultsbeeffectivelydifferentifweconsideredtheeffectofearthsmagneticfield?Youneedtopayattentiontotheearthsmagneticfieldvector(magnitudeanddirection)whenmakingyourarguments.</p><p>Instructionsonhowtosubmitthegraphs:1. Openaworddocumentandtypethenamesofallpresentgroupmembers.2. IfyouneedhelpfindingslopesusingExcel,pleasetalktoyourTA.3. CopyyourExcelgraph(withtitleandaxislabels)toyourWorddocument.4. Printthedocumentandattachittothelab.</p></li></ul>

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