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[latex]\vec F_{12} = \frac{1}{{4\pi \varepsilon _0 }}\frac{{q_1 q_2}}{{r_{12}^2 }}\hat r_{12} \label{Coulomb2}[/latex]

[latex]\vec F_{12} = \frac{1}{{4\pi \varepsilon _0 }}\frac{{q_1 q_2}}{{r_{12}^2 }}\hat r_{12} \label{Coulomb3}[/latex]