Thus, if two
point charges q1, q2 are separated by a distance r in vacuum,
the magnitude of the force (F) between them is given by
2
1
2
q
q
F
k
r
=
(1 1)
How did Coulomb arrive at this law from his experiments Coulomb used a torsion balance*  for measuring the force
between two charged metallic spheres When the separation
between two spheres is much larger than the radius of each
sphere, the charged spheres may be regarded as point charges