A 0.500 cm diameter plastic sphere, used in a static electricity demonstration, has a uniformly distributed 40.0 pC charge on its surface. What is the potential near its surface?

We can find the potential using the equation

V = kQ/r

Where V is the potential, k corresponds to the Coulomb constant

k = 9. 10^9 N N. m^2/C^2, Q is the charge and r is the radius of the sphere (r = 2.5.10^-3 m)

Substituting in the equation we obtain

V = (9. 10^9 N N. m^2/C^2) * (40.10^-12 C) / (2.5.10^-3 m) =

V = 144 V (Potential near its surface)