Suppose the magnitude of the proton charge differs from the magnitude of the electron charge by a

Question:

Suppose the magnitude of the proton charge differs from the magnitude of the electron charge by a mere 1 part in 10⁹.
a. What would be the force between two 2.0-mm-diameter copper spheres 1.0 cm apart? Assume that each copper atom has an equal number of electrons and protons.
b. Would this amount of force be detectable? What can you conclude from the fact that no such forces are observed?