A charge $Q$ is uniformly distributed over the surface of a fixed, thin-walled dielectric tube of radius $R$ and length $H$. There is a thin dielectric rod which is fixed along a diameter of the tube's cross-section located exactly at the middle of the tube. A bead with a charge of the same sign $Q$ can slide without friction along this rod.

Determine the period $T$ of small osillations of the bead around the equilbrium point.

Ratio $\gamma=q/m$ between charge and mass of bead is known. Neglect a gravity.