静电场

电荷 q_1 对电荷 q_2 的作用力为 $vec{F_{12}}~=~{k}~{q_1 q_2}/{{r_12}^2}~vec{e_12}~= {{1}/{4 pi varepsilon_0 }}~{q_1 q_2}/{{r_12}^2}~vec{e_12}$ 简化为： $vec{F}~=~{{1}/{4 pi varepsilon_0 }}~{q_1 q_2}/{vec{r}}$