A dipole — a rigid rod with length of $H$ and charges $+q$ and $-q$ on its end is held on the axis of thin-walled dielectric cylindrical tube with radius of $R$ and height $H$. A charge is distributed on the tube's surface with a density $\sigma$ that dependse on the distance $x$ from the bottom base according to the law: $$\sigma(x)=\sigma_0\sin^2\left(\cfrac{\pi x}{2H}\right),$$where $\sigma_0 > 0$.
Determine the direction and magnitude of the force acting on the dipole in the position where its charges $+q$ and $-q$ are located at the centers of bottom and top bases (points $O$ and $B$), respectively.
