1. The problem statement, all variables and given/known data A charge of 4.1 nC is placed uniformly on a square sheet of nonconducting material, with side 19.0 cm, that lies in a horizontal plane. 1. What is the magnitude of the electric field just above the center of the sheet? The same charge is placed on a horizontal square conducting slab of side 19.0 cm and vertical thickness 1.0 mm. Assume that the charge distributes itself uniformly on the large square surfaces. 2. What is the surface charge density? 3. What is the magnitude of the electric field just below the center of the slab? 2. Relevant equations guass's law, Φ=EA 3. The attempt at a solution 1. use Φ=q/ε=EA so E = q/(εA) plug in numbers, but the answer was wrong. 2. σ = q / A I added up all sides of the slab, but the answer was wrong. 3. i did it the same way i did for 1, the answer was wrong. Would someone kindly tell me what was wrong with my calculation? thanks.