a small circular hole of radius R = 2.03 cm has been cut in the middle of an infinite, flat, nonconducting surface that has a uniform charge density σ = 4.61 pC/m^2. A z axis, with its origin at the hole's center, is perpendicular to the surface. What is the magnitude (in N/C) of the electric field at point P at z = 3.05 cm? (Hint: See Eq. 22-26 and use superposition.)
There is supposed to be a figure, but it really doesn't lend much to this. It is a flat sheet laid on the horizon, with the z axis going through a hole in the middle of the sheet. Point P is on the z axis, and R is just shown as the radius of the hole in the sheet. Which, is pretty much what was said in the problem....
the equation mentioned above is
E = (σ / 2ε) *( 1- z/ (√z^2 + R^2))
but how I'm supposed to use that and superposition, I am not sure.
The Attempt at a Solution
I want to just plug in the given values, but I don't think that it right, because the question mentions superposition, but what am I adding together?! There was an additional hint about using a disc of equal magnitude and such, but oppostire direction. Wouldn't I then need a different equation? Help! (and Thanks)