Electrostatic force on a parallel plate

[serverxeon]

I'm tasked to find the force one parallel plate exert on the other plate in a capacitor.

somehow the force isn't just F=qE, where E=Q/2εA

What am I missing here?

 

[Simon Bridge]

What am I missing here?

Erm - direction?

You can check by using another method ... i.e. Coulombs law for a point charge and add them up, or start with the electric field due to a sheet of charge by itself.

 

[serverxeon]

i mean, my solution is lacking so coefficient.
based on my (confused and vague) understanding, the electric field is actually 1/2 E or something?

 

[Simon Bridge]

Is it? Why not calculate the field?