======静电场======

=====库仑定律=====
电荷<m 15>q_1</m>对电荷<m 15>q_2</m>的作用力为
<m 20> vec{F_{12}}~=~{k}~{q_1 q_2}/{{r_12}^2}~vec{e_12}~= {{1}/{4 pi varepsilon_0 }}~{q_1 q_2}/{{r_12}^2}~vec{e_12} </m>
简化为：
<m 20> vec{F}~=~{{1}/{4 pi varepsilon_0 }}~{q_1 q_2}/{vec{r}} </m>

=====电场强度=====
电场强度定义式：<m 20> vec{E}=vec{F}/q_0 </m>