Two charged spheres are held a distance, r, apart. One sphere has a charge of +4µC, and the other sphere has a
charge of +8µC. Compare the force of the +4µC sphere on the +8µC sphere with the force of the +8µC sphere
on the +4µC sphere.
Being of the same sign (both +ve), the two charges repel one another, and the magnitude of this force is given by Coulomb’s law:
`F = 1/(4piepsilon_o)(q_1*q_2)/r^2`
`=1/(4*pi*8.85419*10^(-12))(4*10^-6*8*10^-6)/ r^2 N`
`= 0.2877/r^2 N`
Each charge exerts a force of repulsion of `0.2877/r^2 N` on the other charge (recall Newton’s third law) .
Therefore, the force of repulsion exerted by the +4µC sphere on the +8µC sphere and the force of repulsion exerted by the +8µC sphere on the +4µC sphere are exactly the same.