1. Positive and negative charges are distributed evenly in two parallel plates with width "w". The density of the positive and negative charge is +[tex]\rho[/tex] and -[tex]\rho[/tex]. Assume that the length of the plates at y direction is [tex]\infty[/tex] (a) Find the electric field in the plates (b) Let the electric potential at x=-w equal to 0, find the electric potential in the plates. 2. Relevant equations [tex]\Delta[/tex]E=k*Delta-Q*r/r2 where r is the unit vector -- (1) 3. My approach I sliced an infinitesimal portion of the plate horizontally denoted as Delta-y and represent the charge Delta-Q = rho *Delta-y*2*w. Is my expression for Delta-Q correct? r is the observation point which is at opposite to the portion Delta-y on the negative plate of which magnitude is "w". Substitute my expression for Delta-Q into (1), I obtain Delta-E = k*rho/w. Do I have to integrate Delta-E from -infinity to +infinity to obtain the electric field in the plates? If so, I will get E=0. Does this make sense? Thank you.