Find the electrostatic potential produced by an extra point charge inside a crystal belonging to the orthorhombic crystal system. begin from the inhomogeneous equation for d, and suitable cartesian coordinates, to find an appropriate generalization of poisson's equation (in cgs units) that takes account of the dielectric tensor; then identify a simple change of variables that transforms this equation into the familiar one for a point charge in vacuum, given the appropriate rescaling of the differential volume element and δ–function charge density. sketch and / or describe an equipotential surface; likewise find and describe the corresponding solutions for crystals belonging to the tetragonal and cubic crystal systems.