- #1
peroAlex
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Homework Statement
At our university we were given this problem: charged ball with mass of ##m = 0.0001 kg## and charge ##Q = -10^{-5} C## is placed on geometric axis of thin torus with inner radius of ##r_{inner} = 0.05 m##, outer radius of ##r_{outer} = 0.1 m## and surface charge density ##\sigma = 10^{-5} C##. Compute oscillation time for small deviation, this is when we only slightly flick the ball from stable state.
Homework Equations
First, I took a look at this article and a PDF presentation.
The Attempt at a Solution
Using the equation for electric field of a charged ring $$ E_z = \frac{Qz}{4 \pi \varepsilon_0 (r^2 + z^2)^{\frac{3}{2}}} $$ I tried obtaining formula for electric field of torus (wider ring) by integration infinitesimal rings from inner to outer radius. Using Symbolab I managed to obtain following equation $$ E_{torus} = \frac{Qz}{4 \pi \varepsilon_0} (\frac{r}{z^3 \sqrt{\frac{r^2}{z^2}+1}})_{r_{inner}} ^ {r_{outer}} $$.
From here on, I'm lost. Can somebody please help me or at least give me some guidance?