# Electric fields of charged plates

• swinfen
In summary, the conversation discusses a problem involving the application of an equation to find the electric field between two charged plates. There is confusion about the relevance of the distance between the plates and the units used in the equation. It is suggested that the answer may be incorrect in the given answer key.
swinfen
Homework Statement
Find the magnitude of the electric field of a large plate with surface charge density of 300Cm2 at a point 2.00 m away from the surface?
Relevant Equations
E = σ/2e0
I thought it might be the case that the "2m away" wasn't applicable as the electric field doesn't change if the point away is less than the length of the plate, so I thought I should use the equation listed. All examples I can find talk about two charged plates, or the effect on cylinders through or around a charged plate.

Hello @swinfen,
You have a relevant equation.
The cylinders are involved in the derivation of the equation.
What stops you from applying it ?

##\ ##

Thanks for your response BvU. Firstly, am I correct that the '2m away' is not relevant? If this is then the only equation to use, then I was marked wrong by the professor (they do not provide any feedback on wrong answers). The answer I gave was:

E = σ/2e0
=> E = 300/2*(8.854*10^-12)
=> E = 1.694*10^13

Perhaps you were punished for omitting the units ?
I can't think of anything else.
The distance should be << plate dimensions, but that is what the problem statement says.

##\ ##

Let me speculate...
The charge density of 300 C/m2 is too large and so is the electric field. As for the distance, it is irrelevant because the plate is large. Many times "large" means infinitely big.

Thanks for the feedback. Yes I realized that I missed the units on this one (only this one!) but even my one of the professors (who I finally managed to get in touch with and had tried to solve the problem) couldn't get the same answer as the answer key. So I think we must be right and the answer key must be wrong!
Now just need to understand the other problem I posted, if any of you would like to help with that one? :)

I can't see the other problem.

## 1. What is an electric field?

An electric field is a region in space where an electrically charged particle experiences a force. It is created by the presence of electric charges and can be represented by electric field lines.

## 2. How are electric fields created by charged plates?

Charged plates create electric fields because the charges on the plates exert a force on other charged particles, causing them to experience an electric field. The strength of the electric field depends on the magnitude and distribution of the charges on the plates.

## 3. What is the direction of the electric field between two charged plates?

The electric field between two charged plates is always perpendicular to the plates, pointing away from the positively charged plate and towards the negatively charged plate.

## 4. How does the distance between charged plates affect the electric field?

The strength of the electric field between two charged plates is inversely proportional to the distance between the plates. This means that as the distance increases, the strength of the electric field decreases.

## 5. Can electric fields of charged plates be manipulated?

Yes, electric fields of charged plates can be manipulated by changing the magnitude or distribution of charges on the plates. This can be done by adding or removing charges, or by changing the distance between the plates.

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