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andthenthelightgoes Theswitchcanalsojointhetwopartsofthewireagain, thenwegetalight Switchcancontrolmanydifferentthings Smallswitchescontrollampsandradiosetsbecausethesedonottakealargecurrent, largerswitchescontrolelectricfires Otherswitchescancontrolelectricmotors Goodswitchesmovequickly Theyhavetostopthecurrentsuddenly Iftheymoveslowly, anelectricsparkappears Itjumpsacrossthespacebetweenthetwoendsofthewire Thisisunsafeanditheatstheswitch Verybigswitchesaresometimesplacedinoil, Sparksdonoteasilyjumpthroughoil, andsotheoilmakestheswitchsaferAlargecurrentmakesawirehot Ifthewireisverythin, evenasmallcurrentmakesithot Thishappensinanelectriclamp Theelectricwiresinahousearecoveredwithsomekindofinsulation Nocurrentcanflowthroughtheinsulation, sothecurrentcanneverflowstraightfromonewiretotheother, buttheinsulationonoldwiresisoftenbroken, thenthecopperofthetwowirescantouch Alargecurrentmayflow, andifthishappens, thewireswillgetveryhot Thenthehousemaycatchfire Fusescanstopthistrouble Afuseisonlyathinwirewhichiseasilymelted Itisfixedinafuse-holder(保险盒) Thefuse-holderismadeofsomematerialwhichcannotburn Alargecurrentmakesthefusehotandthenitmeltsaway Wesaythatthefuse"blows(烧断)" Thewireisbrokenandnocurrentcanflow Sothehousedoesnotcatchfire, butallthelightsandelectricfiresgooutbecausethereisnocurrent Whenafuseblows, somethingiswrong Wemustfindthefaultfirst Perhapstwowiresaretouching Wemustcoverthemwithnewinsulationofsomekind Thenwemustfindtheblownfuseandrepairit Weputanewpieceoffuse- wireintheholder (Sometimeswecanfindtherightfuse- holderbecauseitisratherwarm, buttheothersarecold) Ifwedonotrepairthefaultfirst, thenewfusewillblowimmediately