# Homework Help: Ring of charge

1. Sep 26, 2008

### jaejoon89

For a ring of charge centered about the origin, how would you calculate the charge experienced by a point within the ring of charge but not at the center?

So, I know for a ring of charge dE_x = kdq / r^2 = (k*lambda*ds) / r^2 where ds is the arc length.

Then what do I integrate over?
And does the fact that the point isn't at the center/origin, important?
I'm guessing I need to solve that integral, then determine q.

Last edited: Sep 26, 2008
2. Sep 26, 2008

### tiny-tim

Hi jaejoon89!

You integrate over a small arc, of length r dθ, where θ is the angle from the centre of the ring.

3. Sep 26, 2008

### jaejoon89

How do you find the angle from the center of the ring in this case? Here would you just do the angle from the point (it is off center)?

4. Sep 26, 2008

### Redbelly98

Staff Emeritus
θ is the angle around the ring, taken from the center. Integrate over θ from 0 to 2 pi.

You'll also need to figure out r as a function of θ.