In couloumb’s law the value of the constant k is 1/4pi epsilon naught. Here epsilon naught is the vaccum permittivity. But what actually is permittivity here??
The force of attraction between two charges q1 and q2 placed at a distance r is given by;
F = ( 1 / 4πε ) ( q1 x q2 / r2)
here, ε is the permeability of the medium. The permittivity of free space , εo is 8.854 x 10-12 farad / meter.