Electric field at the point within the sheet

[cupcake]

Homework Statement

A huge (effectively infinite) horizontal nonconducting (epsilon = epsilon_0) sheet 10 cm thick has charge over both faces. The upper face carries a uniform +95 nC/m^2 while the lower face carries a uniform -25.0 nC/m^2. The magnitude of the electric field at a point within the sheet 2.00 cm below the upper face is closest to :

Homework Equations

E= k q/r^2

The Attempt at a Solution

Etotal = E1 + E2

E1 = k q1 / r^2 = 9 * 10^9 * 95 *10^-9 / (0.02)^2 = 2137500

E2 = k q2 / r^2 = 9 * 10^9 * 25 *10^-9 / (0.08)^2 = 35156.25

Etotal = E1+E2 = 2172656.25 N/C

is this correct or not?
Thanks

 

[dx]

Your formula for E is for point charges. For an infinite sheet of charge with surface charge density σ, E is σ/2ε. You can prove this using Gauss' law.