How do you find the electric fields of regions between parallel infinite sheets.

[nontradstuden]

Homework Statement

How do you find the electric fields of regions between parallel infinite sheets of charge?
The set up: 3 parallel infinite sheets of charge a,b,c from left to right.
Region 1 is to the left sheet a.
Region 2 is between sheets a and b.
Region 3 is between sheets b and c.
Region 4 is to the right of sheet c.

They only give you the surface charge densities of each sheet. Each surface charge density is different.

How do I go about finding the electric field E in regions 1,2,3 and 4?

Homework Equations

I know the electric field of an infinite charged plane is E= η/ 2ε_0, but don't know what to do.

The Attempt at a Solution

Lost. I tried adding the electric fields together, but that doesn't give me the correct answer.

Edit: I now have the solution.

 

[jbsteele]

The electric field in region 1 is E_1 = η_a/2ε_0, region 2 is E_2 = (η_b - η_a)/2ε_0, region 3 is E_3 = (η_c - η_b)/2ε_0 and region 4 is E_4 = -η_c/2ε_0.