where \(\hat r_{21}\) is the unit vector from \(Q_2\) to \(Q_1\) and \(r\) is the distance between the two charges, as illustrated in Figure \(\PageIndex{1}\). \(k=8.99\times 10^{9}\text{N}\cdot\text{...where \(\hat r_{21}\) is the unit vector from \(Q_2\) to \(Q_1\) and \(r\) is the distance between the two charges, as illustrated in Figure \(\PageIndex{1}\). \(k=8.99\times 10^{9}\text{N}\cdot\text{m}^{2}\text{/C}^{2}\) is simply a proportionality constant (“Coulomb’s constant”) to ensure that the quantity on the right will have units of Newtons when all other quantities are in S.I.
