Problem 3.21

A ball of radius $R$ is uniformly charged with the volume density $\rho$ . Find the flux of the electric field strength vector across the ball's section formed by the plane located at a distance $r_{0} < R$ from the centre of the ball.

|\Phi|=1 / 3 \pi \rho r_{0}\left(R^{2}-r_{0}^{2}\right) / \varepsilon_{0}

Constant Electric Field in a Vacuum