Electric field between parallel plates

[lys04]

Homework Statement

The electric field outside a conducting plate of charge is given by sigma/epsilon right? Then why not for a capacitor, since that is 2 conducting plates, is the electric field 2sigma/epsilon using superposition principle?

Relevant Equations

E=sigma/epsilon

^^

 

[Steve4Physics]

Here’s a cross -section through (due to space limitations, part of) an infinite conducting plate with a (say) positive charge:
___________________________
___________________________

Here are some questions to consider:
- are both surfaces charged?
- if only one (of the two) surfaces is charged, what determines which one?
- in a static situation, every ‘field line’ starts on a positive charge and ends on a negative charge; where are the negative charges here?

 

[SammyS]

Homework Statement: The electric field outside a conducting plate of charge is given by sigma/epsilon right? Then why not for a capacitor, since that is 2 conducting plates, is the electric field 2sigma/epsilon using superposition principle?
Relevant Equations: E=sigma/epsilon

Generally, the two plates of a capacitor are oppositely charged. Right?

So, if one plate has a surface charge density, $\sigma$, then the other plate has surface charge density, $- \sigma$,

Now use superposition to determine the electric field outside the plates as well as between the plates.

 

[Tom.G]

https://www.google.com/search?hl=en&q=fringing+field+of+finite+parallel-plate+capacitors

 

[haruspex]

https://www.google.com/search?hl=en&q=fringing+field+of+finite+parallel-plate+capacitors

The error in post #1 is much more fundamental than any concerns about fringing effects.