# Homework Help: Electrostatic potential of circular ring

1. Apr 7, 2014

### KiNGGeexD

I'm a little stumped with this problem, I have posted a photograph below as there is a diagram to compliment the question

Expressions which I used where

V(r)= k q/r

Where q= σ da

Where da is an element of area

And k= 1/4πε

I messed around with these expressions for a while but it didn't really go anywhere I was having trouble defining and element of area (to use spherical coordinates or not).

Any help or suggestions would be great thanks in advanced :):):):)

2. Apr 7, 2014

### nasu

What area? It is a ring. You can consider linear charge density.

3. Apr 7, 2014

### KiNGGeexD

Ok so area of the circle is

πr^2

And if I'm assuming linear charger density my equation would become

V(r)= k λ/r dl

4. Apr 7, 2014

### nasu

Do you realize that you will have to integrate over the ring? Have you done any similar problems?

5. Apr 7, 2014

### KiNGGeexD

Yea I realise that but I haven't had a similar problem, most problems have been on the xy plane alone

6. Apr 7, 2014

### nasu

Oh, just now I realized that your point A is on the z axis.
There is an "a" in the xy plane that misled me.

Then is is much simpler than I thought.
If you take a small element of ring with length dl, what will be the charge on this element?
What will be the distance between this element and the point A?

7. Apr 7, 2014

### KiNGGeexD

What I mean is it was a two dimensional problem where lines were the only consideration rather than areas or volumes

8. Apr 7, 2014

### nasu

Oh, here it's the same too. It has nothing to do with areas or volumes.

9. Apr 7, 2014

### KiNGGeexD

The distance between the two points would be

(z^2+ x^2)^1/2

10. Apr 14, 2014

### KiNGGeexD

Would I just use my distance and integrate from -a to a, or rather multiply by 2 and integrate from 0 to a?