Question

在靜電場(chǎng)中，下述說法正確的是（　�。�

A．正電荷由高電勢(shì)處運(yùn)動(dòng)到低電勢(shì)處，電勢(shì)能增加

B．正電荷由高電勢(shì)處運(yùn)動(dòng)到低電勢(shì)處，電勢(shì)能減小

C．負(fù)電荷由低電勢(shì)處運(yùn)動(dòng)到高電勢(shì)處，電勢(shì)能減少

D．負(fù)電荷由高電勢(shì)處運(yùn)動(dòng)到低電勢(shì)處，電勢(shì)能減小

Answer 1

分析：根據(jù)W=qU確定電場(chǎng)力做功的正負(fù)；電場(chǎng)力做正功導(dǎo)致電勢(shì)能減小，做負(fù)功電勢(shì)能增加．場(chǎng)強(qiáng)為零的地方電勢(shì)不一定為零．電勢(shì)為零是人為選取的．而電勢(shì)能除與電勢(shì)有關(guān)外，還與電荷的電量及正負(fù)有關(guān)．

解答：解：正電荷由高電勢(shì)處運(yùn)動(dòng)到低電勢(shì)處，由W=qU有電場(chǎng)力做正功，所以電勢(shì)能減�。蝗粲傻碗妱�(shì)處運(yùn)動(dòng)到高電勢(shì)處，由W=qU有電場(chǎng)力做負(fù)功，所以電勢(shì)能增加．
負(fù)電荷由低電勢(shì)處運(yùn)動(dòng)到高電勢(shì)處，由W=qU有電場(chǎng)力做正功，所以電勢(shì)能減少；若由高電勢(shì)處運(yùn)動(dòng)到低電勢(shì)處，由W=qU有電場(chǎng)力做負(fù)功，所以電勢(shì)能增加．
所以有：只有正電荷在電勢(shì)高處電勢(shì)能一定大，而負(fù)電荷在電勢(shì)高處電勢(shì)能一定小．故A、D錯(cuò)誤；B、C正確   
故選：BC

點(diǎn)評(píng)：通過電場(chǎng)力做功來確定電勢(shì)能的變化，從而形成結(jié)論：正電荷在電勢(shì)高處電勢(shì)能大，負(fù)電荷在電勢(shì)低處電勢(shì)能大．對(duì)于電勢(shì)與場(chǎng)強(qiáng)的大小關(guān)系：兩者沒有關(guān)系，可根據(jù)電勢(shì)高低看電場(chǎng)線的方向，場(chǎng)強(qiáng)大小看電場(chǎng)線疏密來理解．