- #1

Markel

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Where is the magnitude of the Electic field that you end up calculating? I had assumed it would be anywhere on the Gaussian surface, but it doesn't make sense now that I think of it.

for instance, calculating the field of a charged cunducting surface.

The gausian surface is a cylinder, and the left half is within the surface, and the right half is outside the surface.

The calculations show the field is E= (surface charge density)/(permitivity of vacuum)

But where is this field? It can't be along the gausian surface because part of it is within the conductor, where the field is 0, and part is outside where it is definitely not 0.

Also, I don't understand the difference between finding the field due to a conducting surface:

E= (surface charge density)/(permitivity of vacuum)

and the Field from a sheet of charge: E= (surface charge density)/( 2 x (permitivity of vacuum))

What is the difference? Both are simply just a wall of charge. In my book it says that the expression for a conducting surface is only valid very close to the surface ( I assume this is so that we can approximate the surface as a straight plane), but even that makes no difference. The only difference is for the conducting surface, the Gaussian cylinder is protruding into the sheet, and for the second, it pierces the sheet completely and comes out the other side. But why does the electric field change depending on how you draw your gaussian surface? Shouldn't it be for any closed surface? Of any size or shape?

I thought I understood this, but I'm fairly confused. Any help would be appreciated.