Coulomb s Law #8211; If two stationary point charges q<sub>1</sub> and q<sub>2</sub> are kept at a distance r, then it is found that force of attraction or repulsion between them is, F ∝ q<sub>1</sub>q<sub>2</sub>/r<sup>r</sup> [F = kq<sub>1</sub>q<sub>2</sub>/r<sup>2</sup> ] (Where, k is proportionality constant) In SI units the constant k is k = 1/4πε<sub>0</sub> = 9 times; 10<sup>9</sup> N-m<sup>2</sup>/C<sup>2</sup> In vacuum F = 9 times; 10<sup>9/gt;supgt; times; q<sub>1</sub>q<sub>2</sub>/r<sup>2</sup> N where, ε <sub>0</sub> = Absolute permittivity of free space = 8.85 times; 10<sup>-12</sup> C<sup>2</sup> / N-m<sup>2</sup> Its dimensional formula is [M<sup>-1</sup> L<sup>-3</sup> T<sup>4</sup> A<sup>2</sup>].