Problem solved. I realized that the "circles" in question were actually supposed to be cylinders (of unspecified length). In that case, the field generated by the cylinders drops off as 1/r, not 1/r^2 as I had assumed (see...
Homework Statement
Three concentric circles of radii 1.5m, 2.5m, and 4m are filled with a gas that breaks down in electric fields greater than 1.6 x 10^7 volt/meters. What is the highest potential difference that can be maintained between the innermost circle and the outermost circle. (Hint...