E → ( r → ) = 1 4 π ε 0 ∑ i = 1 N R ^ i Q i | R → i | 2 = 1 4 π ε 0 ∑ i = 1 N R → i Q i | R → i | 3 {\displaystyle {\vec {E}}({\vec {r}})={\frac {1}{4\pi \varepsilon _{0}}}\sum _{i=1}^{N}{\frac {{\widehat {\mathcal {R}}}_{i}Q_{i}}{|{\mathcal {\vec {R}}}_{i}|^{2}}}={\frac {1}{4\pi \varepsilon _{0}}}\sum _{i=1}^{N}{\frac {{\vec {\mathcal {R}}}_{i}Q_{i}}{|{\mathcal {\vec {R}}}_{i}|^{3}}}} is the electric field at the field point, r → {\displaystyle {\vec {r}}} , due to point charges at the source points, r → i {\displaystyle {\vec {r}}_{i}} , and R → i = r → − r → i , {\displaystyle {\vec {\mathcal {R}}}_{i}={\vec {r}}-{\vec {r}}_{i},} points from source points to the field point.
