**1. The problem statement, all variables and given/known data**

A flat ring of inner radius R1 and outer radius R2 carries a uniform surface charge density σ. Determine the electric potential at points along the axis (the x axis). [Hint: Try substituting variables.]

**2. Relevant equations**

V = (kQ)/r

**3. The attempt at a solution**

As you can see from my screenshot, I think I’ve figured it out mostly I’m just stuck on finding the value for r in the above equation. Shouldn’t it be something like sqrt(x^2+y^2)? But that can’t be the answer because there’s no labelled y-axis…

http://ift.tt/1eIWJca