Two infinite sheets with charges

[BadSkittles]

Two infinite-plane non-conducting, thin sheets of uniform surface charge p1 = 12.30 uC/m2 and p2 = -3.30 uC/m2) are parallel to each other and d = 0.615 m apart. What is the electric field between the sheets? (Note: the field is positive if it is parallel to the vector x).

Hi, I've tried this problem through the equation

σ/2ε of sheet 1 + σ/2ε of sheet 2= E

but that didnt seem to work. I also thought that maybe all the electric field lines were concentrated in the area between the two sheets since opposite charges attract. So i multiplied by two and that didnt work. Anyone got a clue to this problem?

 

[TSny]

Hello.

I think you have the right idea. Since you didn't show the details of your calculation, it's hard to tell where you made a mistake. Could be an error associated with the signs or directions of the electric fields from the plates.

If you are at a point between the plates, does the electric field, E₂, at that point from the negatively charged plate point in the same direction or the opposite direction as the field E₁ from the positive plate?

 

[voko]

The field from the two sheets is a vectorial sum of each sheet's field. The equation you have is generally correct, but, depending on how exactly the sheets are positioned along the x-axis (and I assume it is perpendicular to both sheets), you may have to mind the signs. That, and a numerical error, are all that I think could go wrong here.

 

[BadSkittles]

Wouldn't you just add the absolute value of both electric fields since the electric fields from both of the plates are headed towards the same direction?

 

[BadSkittles]

I got 880957 N/C as my answer

 

[BadSkittles]

sorry, solved... direction mattered

 

[TSny]

I got 880957 N/C as my answer

That looks correct to me. (You might want to round off your answer to the appropriate number of significant figures.)