電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)是(shi)儲存(cun)(cun)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量(liang)(liang)和(he)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)能(neng)(電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)勢(shi)能(neng))的(de)元件(jian)。一個導(dao)(dao)(dao)體(ti)(ti)(ti)被(bei)另(ling)一個導(dao)(dao)(dao)體(ti)(ti)(ti)所(suo)包圍,或者由一個導(dao)(dao)(dao)體(ti)(ti)(ti)發出(chu)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)場線全部(bu)終止在(zai)另(ling)一個導(dao)(dao)(dao)體(ti)(ti)(ti)的(de)導(dao)(dao)(dao)體(ti)(ti)(ti)系,稱為(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)既然是(shi)一種儲存(cun)(cun)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)的(de)“容(rong)(rong)(rong)器(qi)”,就有(you)“容(rong)(rong)(rong)量(liang)(liang)”大小的(de)問題。為(wei)(wei)了衡量(liang)(liang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)儲存(cun)(cun)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)的(de)能(neng)力,確(que)定(ding)了電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)量(liang)(liang)這個物理量(liang)(liang)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)須(xu)在(zai)外(wai)(wai)加電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)作用(yong)下才能(neng)儲存(cun)(cun)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)。不(bu)同的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓作用(yong)下儲存(cun)(cun)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)量(liang)(liang)也可能(neng)不(bu)相(xiang)同。國際上統(tong)一規定(ding),給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)外(wai)(wai)加1伏特直流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓時(shi),它所(suo)能(neng)儲存(cun)(cun)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)(he)量(liang)(liang),為(wei)(wei)該(gai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)量(liang)(liang)(即單位電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓下的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量(liang)(liang)),用(yong)字母(mu)C表示(shi)。