小功率電阻器通常為封裝在塑料外殼中的碳膜構成，而大功率的電阻器通常為繞線電阻器，通過將大電阻率的金屬絲繞在瓷心上而制成。
 
    如果一個電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)值(zhi)接近零歐(ou)姆(例如，兩(liang)個點(dian)之(zhi)間的(de)(de)(de)大(da)(da)截(jie)面導(dao)線)，則該電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)對電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)沒有(you)阻(zu)(zu)(zu)(zu)(zu)礙(ai)作(zuo)用(yong)，并聯(lian)這種電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)的(de)(de)(de)回路(lu)被短(duan)路(lu)，電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)無(wu)限(xian)(xian)大(da)(da)。如果一個電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)具(ju)有(you)無(wu)限(xian)(xian)大(da)(da)的(de)(de)(de)或很大(da)(da)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)，則串接該電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)的(de)(de)(de)回路(lu)可(ke)看作(zuo)開路(lu)，電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)為(wei)零。工業中(zhong)常(chang)(chang)用(yong)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)介(jie)于兩(liang)種端(duan)情(qing)況(kuang)之(zhi)間，它具(ju)有(you)一定(ding)(ding)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)，可(ke)通(tong)過一定(ding)(ding)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，但電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)不像短(duan)路(lu)時(shi)(shi)那樣(yang)大(da)(da)。電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)的(de)(de)(de)限(xian)(xian)流(liu)(liu)作(zuo)用(yong)類(lei)似(si)于接在兩(liang)根大(da)(da)直徑管子之(zhi)間的(de)(de)(de)小直徑管子限(xian)(xian)制水(shui)流(liu)(liu)量的(de)(de)(de)作(zuo)用(yong)。電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)，英(ying)文名resistance，通(tong)常(chang)(chang)縮寫為(wei)R，它是(shi)(shi)導(dao)體(ti)的(de)(de)(de)一種基本(ben)(ben)性質，與導(dao)體(ti)的(de)(de)(de)尺寸、材(cai)料、溫度有(you)關。歐(ou)姆定(ding)(ding)律說(shuo)，I=U/R，那么R=U/I，電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)的(de)(de)(de)基本(ben)(ben)單(dan)位是(shi)(shi)歐(ou)姆，用(yong)希臘字母(mu)"Ω"表示(shi)，有(you)這樣(yang)的(de)(de)(de)定(ding)(ding)義:導(dao)體(ti)上(shang)加上(shang)一伏特(te)電(dian)(dian)(dian)(dian)(dian)壓時(shi)(shi)，產(chan)生一安培電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)所(suo)對應的(de)(de)(de)阻(zu)(zu)(zu)(zu)(zu)值(zhi)。電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)的(de)(de)(de)主(zhu)要職能就是(shi)(shi)阻(zu)(zu)(zu)(zu)(zu)礙(ai)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)流(liu)(liu)過。事(shi)實上(shang)，"電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)"說(shuo)的(de)(de)(de)是(shi)(shi)一種性質，而通(tong)常(chang)(chang)在電(dian)(dian)(dian)(dian)(dian)子產(chan)品中(zhong)所(suo)指的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)，是(shi)(shi)指電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)這樣(yang)一種元件(jian)。歐(ou)姆常(chang)(chang)簡稱為(wei)歐(ou)。表示(shi)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)阻(zu)(zu)(zu)(zu)(zu)值(zhi)的(de)(de)(de)常(chang)(chang)用(yong)單(dan)位還有(you)千歐(ou)(kΩ)，兆(zhao)歐(ou)(MΩ)，毫(hao)歐(ou)(mΩ）。