The forces measured by AFM arise primarily from interactions between electrons of the stylus and on the surface. To get an idea of the magnitudes of these forces, calculate the force acting between two electrons separated by 2.0 nm Hints. The Coulombic potential energy of a charge q1 at a distance r from another charge q, is
V = q1q2/4πε 0r
Where ε0 = 8.854 X 10-12 C2 J-1 m-1 is the vacuum permittivity. To calculate the force between the electrons, note that F = -d V/ dr,