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1、Electricityaroundtheworld Thereisnostandardmainsvoltagethroughouttheworldandalsothefrequency,i.e.thenumberoftimesthecurrentchangesdirectionpersecond,isnoteverywherethesame.Moreover,plugshapes,plugholes,plugsizesandsocketsarealsodifferentinmanycountries.Thoseseemingly
2、unimportantdifferences,however,havesomeunpleasantconsequences.Mostappliancesboughtoverseassimplycannotbeconnectedtothewalloutletsathome.Thereareonlytwowaystosolvethisproblem:youjustcutofftheoriginalplugandreplaceitwiththeonethatisstandardinyourcountry,oryoubuyanunhan
3、dyanduglyadapter.Whileitiseasytobuyaplugadapteroranew"local"plugforyour"foreign"appliances,inmanycasesthisonlysolveshalftheproblem,becauseitdoesn'thelpwiththepossiblevoltagedisparity.A110-voltelectricalappliancedesignedforuseinNorthAmericaorJapanwillprovideanicefirew
4、orksdisplay-completewithsparksandsmoke-ifpluggedintoaEuropeansocket.Itgoeswithoutsayingthatthelackofasinglevoltage,frequencyandgloballystandardisedplugsentailmanyextracostsformanufacturersandincreasetheburdenontheenvironment.Purewasteandunnecessarypollution! Voltagea
5、ndfrequencyEuropeandmostothercountriesintheworlduseavoltagewhichistwicethatoftheUS.Itisbetween220and240volts,whereasinJapanandinmostoftheAmericasthevoltageisbetween100and127volts.Thesystemofthree-phasealternatingcurrentelectricalgenerationanddistributionwasinventedby
6、anineteenthcenturycreativegeniusnamedNicolaTesla.Hemademanycarefulcalculationsandmeasurementsandfoundoutthat60Hz(Hertz,cyclespersecond)wasthebestfrequencyforalternatingcurrent(AC)powergenerating.Hepreferred240volts,whichputhimatoddswithThomasEdison,whosedirectcurrent
7、(DC)systemswere110volts.PerhapsEdisonhadausefulpointinthesafetyfactorofthelowervoltage,butDCcouldn'tprovidethepowertoadistancethatACcould.WhentheGermancompanyAEGbuiltthefirstEuropeangeneratingfacility,itsengineersdecidedtofixthefrequencyat50Hz,becausethenumber60didn'
8、tfitthemetricstandardunitsequence(1,2,5).Atthattime,AEGhadavirtualmonopolyandtheirstandardspreadtotherestofthecontinent.InBritain,d
