Anordinaryelectricweldingmachineisaspecialtransformer.Thedifferenceisthatthevoltagedropis***allwhenthetransformerisconnectedtotheload,andthevoltagedecreasesgreatlywhentheweldingmachineisconnectedwiththeload.Thisismainlyachievedbyadjustingthefluxandtheinductanceofseriesinductors.Althoughthecircuitisclosed,itispreciselybecausethecircuitisclosedthatthecurrentisequaleverywhereinthewholeclosedcircuit;Butresistorsvaryfromplacetoplace,especiallyatunfixedcontacts,whicharecalledcontactresistorsinphysics.Accordingtothelawofthethermaleffectofcurrent(alsoknownasJoule'slaw),QI^2rtshowsthatifthecurrentisequal,thegreatertheresistance,thehighertheheat,andthemaximumcontactresistancebetweenthecontactoftheelectrodeandthemetalbodyintheweldingprocess.Thenthenumberofelectricheatingproducedinthispartisthemost.Theelectrodeisalsothealloywithlowermeltingpoint.Naturally,itiseasytomelt,andthemeltedalloyelectrodecogsontotheobjecttobewelded.)