# Electric Charge and Electric Fields

Each quare centimeter of the surface of an infinite p;ane sheet of paper has 2.5 X 10^6 excess electrons. Find the magnitude and direction of the electric field at a point 5 cm from the surface of the sheet, if the sheet is large enough to be treated as an infinite plane.

This is an odd problem and the answer is:
226 N/C towards the sheet

I understant why it is towards the sheet. I am guessing that since it is an infinite plane the 5 cm distance is unimportant.

does this have something to do with the equation: E = 2*sigma / 2*Eo

Thanks!

nrqed
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aquabug918 said:
Each quare centimeter of the surface of an infinite p;ane sheet of paper has 2.5 X 10^6 excess electrons. Find the magnitude and direction of the electric field at a point 5 cm from the surface of the sheet, if the sheet is large enough to be treated as an infinite plane.

This is an odd problem and the answer is:
226 N/C towards the sheet

I understant why it is towards the sheet. I am guessing that since it is an infinite plane the 5 cm distance is unimportant.

does this have something to do with the equation: E =sigma / 2*Eo

Thanks!

Yes, that's the basic idea (except that the equation is 2 sigma /(2 epsilon_0).

That's all there is to it.
(you know how to calculate sigma, I assume. Just take the number of excess electrons times the charge of one electron divided by the 1 cm^2. Don't forget that 1cm^2 = 10^(-4) m^2).

EDIT: I retyped the wrong equation by mistake. Sorry. It is of course sigma/(2 epsilon_0)

Patrick

Last edited:
Thanks a lot, i understand it better now!