# Potential between two infinite plates with the same charge.

## Main Question or Discussion Point

I'm trying to understand electrical potential and have a couple thought questions (Part A and part B)

Part A

Is it possible to calculate the potential of point between to infinite plates having the same positive charge?

I know the electric field is zero between the plates but it would be constant out side the plates. So i'm assuming the potential out side of an infinite plate would be infinite. So would that mean that any point in between the two plates would also be infinite? I suppose if this is true that in real life plates are not infinite and the farther you get from the plates they would look more like a point charge.

Part B
If I have 4 charges: -2C, 4C, -3C, 1C spaced "L" from a center point and if I'm wondering what the potential of a point a distance of R from the center point if R>>L .

If R is much greater than L then I'm thinking I could just add the charges together and then V would be

V = kQ/R where Q = 0 for this case so the Potential would be 0. Is this correct?

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Ben Niehoff
Gold Member
I'm trying to understand electrical potential and have a couple thought questions (Part A and part B)

Part A

Is it possible to calculate the potential of point between to infinite plates having the same positive charge?
Yes, but you can't choose infinity as your zero point. The same issue arises with trying to find the potential of an infinite wire.

Part B
If I have 4 charges: -2C, 4C, -3C, 1C spaced "L" from a center point and if I'm wondering what the potential of a point a distance of R from the center point if R>>L .

If R is much greater than L then I'm thinking I could just add the charges together and then V would be

V = kQ/R where Q = 0 for this case so the Potential would be 0. Is this correct?
The monopole moment would be zero, yes, but depending on the shape of the charge configuration, the higher moments might not be zero. Have you covered multipole moments yet?

(Note: If you get sufficiently far away from any finite charge distribution, the potential goes to zero! So I don't think your answer is specific enough)