# Electric fields at points?

Hi,

1. Homework Statement

You've hung two very large sheets of plastic facing each other with distance d between them, as shown in Figure P26.50 ( http://i137.photobucket.com/albums/q208/infinitbelt/p26-50-1.gif [Broken]... ). By rubbing them with wool and silk, you've managed to give one sheet a uniform surface charge density n1 = -4(n0) and the other a uniform surface charge density n2 = 5(n0). What is the electric field vector at points 1, 2, and 3?

2. The attempt at a solution

I drew the force diagrams for the three points but that is where I think I am making my mistake. For example, for point 1, I have a force going to the left from the positive plate and a force going to the right from the negative plate. The difference I get is 1(n0), but that is wrong. Any ideas?

Thanks!

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Any ideas?

Thanks!

marcusl
Gold Member
Use the expression (probably in your book?) for the electric field from a uniformly charged sheet. The field at each point is a superposition (sum) of the fields from the two sheets.

For my own clarification; is "n0" a given surface charge density?

Use the expression (probably in your book?) for the electric field from a uniformly charged sheet. The field at each point is a superposition (sum) of the fields from the two sheets.

For my own clarification; is "n0" a given surface charge density?

There is no numerical value given to "n0" in the problem. It is like -4x and 5x.

Thank you for the help!

marcusl
Gold Member
Ok, then the answer will appear as a factor of the electric field from n0.

What is the expression for the electric field due to the rectangular sheet?

In my book it is not present. I tried doing the derivation but the integral that I come up with when dividing the sheet into rods doesn't look nice to do. Could you do me the favor and show the expression? Thank you.

marcusl
$$E=\frac{\sigma}{2\epsilon_{0}}$$