- #1

Physicianist

- 3

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## Homework Statement

The problem is:

If you have 2 rectangular plates 1cmx10cm each, which means that the area is A=10cm

^{2}=10

^{-3}m

^{2}for each plate; every plate holds a

__Constant__positive charge of Q=+2x10

^{-6}C each; these plates are separated by a distance d=1cm=10

^{-2}m

What is the electrostatic repulsive force between these 2 plates?

## Homework Equations

1)I've searched all around the internet and only found the formula for 2 narrow parallel plates (d<<the dimensions of the plates), which is not the case here:

F=Q

^{2}/(2Cd)

where C is the capacitance of the capacitor formed between these 2 plates(however these plates do not actually form a capacitor with one another because both have the same charge).

2) C= ε

_{0}xA/d (these plates are separated by air)

3) From 1) and 2) I get this result: F=Q

^{2}/(2ε

_{0}xA)

Which means that the electrostatic force between 2 narrow plates doesn't change with a little increase in the distance d between them ??!

4) I've also found somewhere on the internet that when the dimensions of the 2 plates aren't infinite relatively to the distance between them, there is a correction factor you should multiply F with, which (is 1+2d/D) where D is the diameter of the plates if they are circular or the square root of their area if they are rectangular. This factor takes into account something called the edge forces that increase with the distance d between the plates. If I multiply F with this factor, I got F increasing with distance between the plates instead of decreasing (which I think is more logical,isn't it)

That's why I urgenly need someone to tell me if I'm on the right track or not because I'm very confused with all that. Every help is welcomed, especially if someone from the admin or an expert in physics or engineering would like to interfere

## The Attempt at a Solution

If I take the formulas above, I get F=227,27N without the presumed correction factor

and F=371N after multiplication of F with the correction factor.