- #1

sa1988

- 222

- 23

## Homework Statement

Magnitude of electric field between two concentric oppositely charged spheres.

## Homework Equations

## The Attempt at a Solution

So I first went with the simple electric field equation E=V/d

So I have the potential difference V between the two sphere surfaces. I can't do Latex but hyperphysics has it anyway:

So I know V.

And surely, in E=V/d, the distance d is simply b-a.

So finally I sub my V and d into the equation and I'm left with:

E = Q/(4πεab)

Which looks reasonable enough.. But all sources on the Internet tell me that the answer is simply:

E=Q/4πεr

^{2}

The real confusing thing for me here is... What is 'r' ? What is it the radius from? The radius from the centre? Or from the surface of the inner sphere? Or something else..??

I fear my problem may be with the fact that I used E=V/d, which is possibly only valid for charged plates, rather than spheres? Either way, I'm still a little confused about what the 'r' actually means in the correct answer.

Thanks for any guidance :thumbs: