Acoaxial cable consists of an inner conductor or radius ri = 0.40 cm and an outer conductor of radius ro. when manufactoring such a cable, its size is determined by the voltage between the two conductors and by the insulating material used to insulate the two conductors from each other. we want to calculate an appropriate size for the following cable: assume that the concentric insulating layers are rubber, with dielectric constant εr = 3.2, and polystyrene with dielectric constant εp = 2.6. if we want this cable to have a rating of 20 kv, what should the outer radius ro and the radius rp be? assume that the maximum electric field in the insulating layers should not exceed 25% of their dielectric strength (that is a conservative estimate, in order to avoid breakdowns due to power surges assume that the inner conductor carries linear charge density rho. use the following data: dielectric strength of rubber = 25 × 106 v/m dielectric strength of polystyrene = 20 × 106 v/m