From Coulomb's law, the force between two charges separated by a distance, r, is:

$\overline{){\mathbf{F}}{\mathbf{=}}\frac{\mathbf{k}{\mathbf{q}}_{\mathbf{1}}{\mathbf{q}}_{\mathbf{2}}}{{\mathbf{r}}^{\mathbf{2}}}}$, where k is Coulomb's constant and q_{1} and q_{2} are the charges in the two spheres.

The charge on either sphere is:

$\begin{array}{rcl}{\mathbf{q}}_{\mathbf{1}}\mathbf{=}{\mathbf{q}}_{\mathbf{2}}& \mathbf{=}& \mathbf{n}\mathbf{e}\\ & \mathbf{=}& \mathbf{(}\mathbf{5}\mathbf{.}\mathbf{00}\mathbf{\times}{\mathbf{10}}^{\mathbf{4}}\mathbf{)}\mathbf{(}\mathbf{-}\mathbf{1}\mathbf{.}\mathbf{6}\mathbf{\times}{\mathbf{10}}^{\mathbf{-}\mathbf{19}}\mathbf{)}\end{array}$ (Remember that the charge of an electron is - 1.6 × 10^{-19}C).

q_{1} = q_{2} = - 8.00 × 10^{-15} C

Two small tiny conducting spheres, both initially having no charge, are brought into contact and given a total charge of 5.00x10^{4} electrons. The spheres are then pulled apart until their centers are 12.0 cm apart. Assume the total number of electrons on the spheres remained the same as they were separated.

a) What is the magnitude of the force that each sphere exerts on the other?

b) Is the force attractive or repulsive?

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