Consider the vacuum diode problem treated in the text with the space between the plates filled with a poor conductor with dielectric permittivity ϵ. For matter of this kind, v = ũE, where the mobility ũ is the constant of proportionality between the drift velocity of the electrons and the electric field in the matter. Find the replacement for the Child-Langmuir law for the dependence of the maximum current density on the material constants, the plate separation L, and the plate potential difference V.