4．电偶极子P在外电场E_e中所受的力为(    )
   A．(P·)E_e    B．-(P·E_e)
   C．(·P)E_e    D．(·E_e)P

若f(x)在[a、b]上可积，且f(x)≥0，则______． 点击查看答案

电导率为σ1和σ2，电容率为ε1和ε2的均匀导电介质中有稳恒电流，则在两导电介质分界面上电势的法向微商满足的关系为( ) A． B． C． D．

A.B.174.24.96:6088/Latex/latex.action?latex=XGZyYWN7XHBhcnRpYWwgXHBoaSBfezF9fXtccGFydGlhbCBufT1cZnJhY3tccGFydGlhbCBccGhp%0D%0AIF97Mn19e1xwYXJ0aWFsIG59'
C.D.174.24.96:6088/Latex/latex.action?latex=XHZhcmVwc2lsb24gX3syfVxmcmFje1xwYXJ0aWFsIFxwaGkgX3syfX17XHBhcnRpYWwgbn0tXHZh%0D%0AcmVwc2lsb24gX3sxfVxmcmFje1xwYXJ0aWFsIFxwaGkgX3sxfX17XHBhcnRpYWwgbn09LVxzaWdt%0D%0AYSA%3D'
E.F.174.24.96:6088/Latex/latex.action?latex=XHNpZ21hICBfezF9XGZyYWN7XHBhcnRpYWwgXHBoaSBfezF9fXtccGFydGlhbCBufT1cc2lnbWEg%0D%0AIF97Mn1cZnJhY3tccGFydGlhbCBccGhpIF97Mn19e1xwYXJ0aWFsIG59'
G.H.174.24.96:6088/Latex/latex.action?latex=XGZyYWN7MX17XHNpZ21hICBfezJ9fVxmcmFje1xwYXJ0aWFsIFxwaGkgX3syfX17XHBhcnRpYWwg%0D%0Abn09XGZyYWN7MX17XHNpZ21hICBfezF9fVxmcmFje1xwYXJ0aWFsIFxwaGkgX3sxfX17XHBhcnRp%0D%0AYWwgbn0%3D'

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