# Finding the charge

**Classical Mechanics**Level 4

Two fixed, non-conductive, isolated rings of radii \(25~\mbox{cm}\) are electrified and brought close to each other so that they are parallel. The distance between them is \(1~\mbox{m}\). You know that one of them has a charge of \(1~\mbox{nC}\) evenly distributed on it, but you are not sure about the other. In order to find out what's the charge on the other, you take a charged ball and move it across the axis of the rings until you find its equilibrium position. You measure where that is and get that the equilibrium position is \(25~\mbox{cm}\) from the center of the ring with the known charge. What's the charge **in nC** of the second ring?

**Details and assumptions**

- The second ring also has evenly distributed positive charge on it.