At the center of a hollow hemisphere uniformly charged with a surface charge density $\sigma ,$ there is a small dipole of dipole moment $\rho .$ The moment of inertia about the rotation axis is I.

The magnitude of $\overrightarrow{E}$ due to hemisphere at the center of hemisphere is $\frac{\sigma }{2{\in }_0}$

The minimum potential energy of dipole is $-\rho \frac{\sigma }{4{\in }_0}$

The dipole performs SHM for small angular displacements with angular frequency is $\omega =\sqrt{\frac{\rho E}{I}}$

If dipole is released from rest from a position perpendicular to the symmetry axis, the maximum KE of dipole is $\frac{\sigma \rho }{4{\in }_0}$