Electric field between parallel plates

AI Thread Summary
The discussion focuses on the electric field between parallel plates of a capacitor, emphasizing that each plate carries opposite charges, with one plate having a surface charge density of σ and the other -σ. It raises questions about the nature of charge distribution on the plates and the presence of negative charges in a static electric field scenario. The electric field outside a single conducting plate is described by the equation E = σ/ε, while the field between two plates is derived using the superposition principle. The conversation highlights a fundamental misunderstanding regarding the application of these principles to capacitors. Overall, the interaction of electric fields in capacitors is crucial for understanding their behavior in static situations.
lys04
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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
^^
 
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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?
 
lys04 said:
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.
 
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