Problem 3.77

A uniform isotropic dielectric is shaped as a spherical layer with radii $a$ and $b$. Draw the approximate plots of the electric field strength $E$ and the potential $\varphi$ vs the distance $r$ from the centre of the layer if the dielectric has a certain positive extraneous charge distributed uniformly: (a) over the internal surface of the layer; (b) over the volume of the layer.