Question

Two 2.0-cm-diameter disks face each other, 1.0 mm apart. Theyare charged to +10 nC and -10 nC. What is the electric fieldstrength between the disks?

I solved the surface charge density to be n=3.183*10^-5(C/m^2)

I then used that in the equation

E field = n/2e0 (1-(1/sqrt(1 + (R^2/Z^2))))

for n/2e0 I got 1.798*10^6 (N/C) and I multiplied that withthe value in the parenthasis

(0.9500624) to get an answer of E =1.708*10^6 (N/C)

Because the question asks what the electric field strength isbetween the disks I used the midpoint in my calculation wich wouldbe 0.0005 meteres. I then multiplied the value I got for E by twoto get 3.42*10^6 (N/C) for my final answer which is wrong. I havegone over the problem several times but I always end up with thesame answer. Can you show me how to solve the problem?