An infinite line charge is at the axis of a cylinder of length $1 \mathrm{m}$ and radius $7 \mathrm{cm}.$ If electric field at any point on the curved surface of cylinder is $250 \mathrm{N} {\mathrm{C}}^{-1}$, then, net electric flux through the cylinder is

A small conducting sphere is hanged by an insulating thread between the plates of a parallel plate capacitor as shown in figure. The net force on the sphere is

The given figure shows, two parallel plates $A$ and $B$ of charge densities $+\sigma$ and $-\sigma$ respectively. Electric intensity will be zero in region