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.

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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.

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