電(dian)(dian)(dian)(dian)(dian)路是(shi)閉合的(de)(de)，使得(de)在整(zheng)個(ge)閉合電(dian)(dian)(dian)(dian)(dian)路和電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)處(chu)處(chu)相等(deng)；但各處(chu)的(de)(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)可(ke)是(shi)不一樣的(de)(de)，特別是(shi)在不固定接觸(chu)處(chu)的(de)(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)最(zui)(zui)大(da)，這個(ge)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)在物理(li)中叫接觸(chu)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)。根據(ju)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)熱(re)效(xiao)應定律（也叫焦(jiao)爾定律），Q=I^2;×Rt可(ke)知，電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)相等(deng)，則(ze)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)越(yue)大(da)的(de)(de)部位發熱(re)越(yue)高，電(dian)(dian)(dian)(dian)(dian)焊在焊接時柱(zhu)頭電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)最(zui)(zui)大(da)，則(ze)在這個(ge)部位產生(sheng)的(de)(de)電(dian)(dian)(dian)(dian)(dian)熱(re)自然也就(jiu)最(zui)(zui)多(duo)，當(dang)柱(zhu)頭將橫徑縱徑壓在一起時釋放出很大(da)的(de)(de)熱(re)量，使得(de)橫徑縱徑瞬間(jian)溶解粘(zhan)結。