Electric Field between two metal plates

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Homework Help Overview

The problem involves calculating the electric field between two parallel metal plates with given charges and dimensions. The context is within electrostatics, specifically focusing on the behavior of electric fields generated by charged plates.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to relate capacitance to the electric field but expresses uncertainty about the correct approach. Some participants suggest using the electric field equation for uniformly charged plates and mention Gauss' law for deriving the electric field.
  • There is discussion about the application of the electric field equation for sheets and the need to consider the distance between the plates, with questions about how this distance affects the calculations.

Discussion Status

Participants are exploring different equations and concepts related to electric fields between charged plates. Some guidance has been provided regarding the use of Gauss' law and the approximation of infinite planes, but there is still uncertainty about incorporating the distance between the plates into the calculations.

Contextual Notes

The problem setup includes specific dimensions and charge values, and there is an acknowledgment that the distance between the plates is small relative to their size, which may influence the applicability of certain approximations.

skibum143
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Homework Statement


Two square metal plates are placed parallel to each other, separated by a distance d= 2.34 cm. The plates have sides of length L= 0.750 m. One of the plates has charge Q=+ 2.70 x10-3 Coulombs, while the other plate has charge -Q. What is the magnitude of the electric field between the plates, not close to the edge?


Homework Equations


C = AE0 / d
E = kQ/r


The Attempt at a Solution


I know how to find the capacatance of the plates, but I don't know how to translate that to the electric field?
I tried to just use kQ/r, but that was incorrect. I'm not sure where I'm going wrong, could someone help?
Thanks!
 
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Hello skibum143,

E = kQ/r won't help you with this problem. That equation is more akin to the electric field for a line (wire) charge. You should start with an equation that applies to the electric field of a uniformly charged plate (plane). If you can't find one, you can use Gauss' law to derive it for an infinite plane, and use that as an approximation here. Then use superposition to combine the respective electric fields of each plate.
 
If I use the equation for the E field of a sheet, it's Esheet = sigma (q/area) / 2E0.
If I do 2 * the answer for the two sheets, I get 5.4E8 N/C.

However, don't I need to factor in the distance between the plates? I'm not sure how to do that...
 
skibum143 said:
If I use the equation for the E field of a sheet, it's Esheet = sigma (q/area) / 2E0.
If I do 2 * the answer for the two sheets, I get 5.4E8 N/C.

However, don't I need to factor in the distance between the plates? I'm not sure how to do that...

The distance between the plates is small compared to the length of each side of the plates. That means the approximation of using an infinite plane should be pretty good in the region "between the plates, not close to the edge."
 
I see! Thank you for your help!
 

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