北大高等分析.electronics.ppt

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1、高等分析化学Electronics•Allmodernanalyticalinstrumentsemployelectronictransducers.Weneedamodestunderstandingofrudimentaryelectronicstobeabletouseandmaintainmoderninstrumentation.CurrentConvention•Allmatterconsistsofpositivelychargednucleisurroundedbyabalancingnumb

2、erofnegativelychargedelectrons.•Electricaldevicesfunctionbycontrollingtheflowofelectrons.•Becauseofhistory,electricalcircuitshavealwaysbeenanalyzedontheassumptionthatelectricalcurrentistheflowofpositivecharge.•Allcircuitbehaviourcanbecorrectlyanalyzedbasedon

3、thisassumption,eventhoughweknowitisreallyelectronsmoving.•CURRENTCONVENTION:Electricalcurrentflowsfromaregionofpositivepotentialenergytoaregionofmorenegative(lesspositive)potentialenergy.Charge•Electricalchargeisafundamentalpropertyofmatter.Thechargeonanelec

4、tronisthesamemagnitudebutofanoppositesigntothatofaproton.•Wehavechosenthelabels“positive”and“negative”todistinguishthem.•ChargeismeasuredinunitsofCOULOMBS(C)andisrepresentedbyQ.•Chargeofanelectronis1.6022x10-19C.•Turnthisaroundandnotethatthereare6.2414x1018e

5、–inaCoulombofcharge.•Inamoleofe–thereis96485.31Cofcharge.ThisnumberiscalledtheFaradayconstant.Itisusedtoconvertelectricalmeasurements(likecurrent)intochemicalmeasurements(likemoles).PotentialEnergy•Matterlikestobeelectricallyneutral.Ifwetrytoseparateapositiv

6、echargefromanegativecharge,itrequireswork(energy).Similarly,bringingtogethertwolikechargesrequiresenergy.•Thepotentialenergydifferencebetweentwosuchparticlesiscalledtheelectricalpotentialdifferenceortheelectromotiveforce(emf).•Thispotentialenergydifferenceis

7、measuredinjoulesofenergyneededpercoulombofchargeseparationandhastheunitofvolt(V).1V=1J/C•Inthespacebetweentwoseparatedcharges,anelectricfieldissaidtoexistwhereintheemfchangescontinuouslywhenmovingfromonechargetotheother.MobileCharges•Anionisformedwhenanelect

8、ronisremovedfrom(cation)oraddedto(anion)aneutralatomormolecule.•Matter(atoms,molecules,andbulkmatter)isheldtogetherbytheattractiveforcebetweenoppositelychargedparticles.Thisisdonebythesharingoft