Two parallel plane sheets 1 and 2 carry uniform charge densities σ1 and σ2 (see Fig. 20.8). The electric field in the region marked I is (σ1>σ2). (Consider the right direction as the positive direction)
The left sheet 1 produces a field of magnitude E1=σ12ϵ0 which points away from it, to the left in region I and to the right in regions II and III. The right sheet 2 produces a field of magnitude E2=σ22ϵ0 which points away from it, to the left in regions II and I and to the right in region III. If σ1>σ2>0 the field in each region from the principle of superposition will be as follows:
Region I : E=12ϵ0(σ1+σ2) towards left.
Region II: E=12ϵ0(σ1−σ2) towards right.
Region III: E=12ϵ0(σ1+σ2) towards right.