Two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and of magnitude 17.0 × 10–22 C/m2. What is E: (a) in the outer region of the first plate, (b) in the outer region of the second plate, and (c) between the plates?
Given:
Surface charge density on plate A, σA = -17.0 × 10-22 Cm-2
Surface charge density on plate B, σB = 17.0 × 10-22 Cm-2
The arrangement of plates are as shonw:
Let electric field in region 1 = E1
Region 2 = E2
Region 3 = E3
The electric field in region I and region III is zero because no charge is present in these regions.
E1 = 0
E2 = 0
We know that,
E3 = σ/ε0 ...(1)
Where, σ 
Surface charge density
ε0 = permittivity of free space
ε0 = 8.85 × 10-12N-1 m-2C2
Now, plugging the Values in equation (1).
⇒ 
⇒ E3 = 1.92 × 10-10 NC-1
The electric field in the region enclosed by the plates is found to be 1.92 × 10-10 NC-1.
The electric field in region III is 1.92 × 10-10 NC-1.