Physics Forums (http://www.physicsforums.com/index.php)
-   Classical Physics (http://www.physicsforums.com/forumdisplay.php?f=61)
-   -   Uniform Electric Fields (http://www.physicsforums.com/showthread.php?t=664233)

 datsqnp Jan14-13 10:30 AM

Uniform Electric Fields

1 Attachment(s)
Coulomb's Law
F = kqq/r^2

Why does the intensity of a uniform electric field not get weaker in the middle? I would understand this if the intensity over distance was a linear function, but it isn't. The force near one of the plates would approach infinity, because r^2 is so small... but in the middle of the field even the forces of each side added up would not approach infinity, which means the field is not uniform. How are uniform electric fields possible?

 ZapperZ Jan14-13 10:43 AM

Re: Uniform Electric Fields

This is a very confusing post.

The expression for the Coulomb's law that you wrote is for a point or spherical charge distribution. Yet, you are talking about "plates" here.

For an infinite planar charge distribution, use Gauss's law and figure out the expression for the E-field. It is NOT the same as what you have written.

Zz.

 jtbell Jan14-13 11:07 AM

Re: Uniform Electric Fields

Or, you can find the electric field produced by a uniform plane sheet of charge by treating it as a collection of point charges and integrating over the whole sheet. If the sheet is large enough to be effectively "infinite" in size, you get the result that the field is uniform on either side of the sheet, in opposite directions on the two sides. (Using Gauss's Law is much quicker, if you know it and understand it.)

 All times are GMT -5. The time now is 05:43 PM.