Coaxial conducting cylinders are located at = 0.5 cm and = 1.2 cm. The region

Coaxial conducting cylinders are located at ρ = 0.5 cm and ρ = 1.2 cm. The region between the cylinders is filled with a homogeneous perfect dielectric. If the inner cylinder is at 100 V and the outer at 0 V, find

(a) The location of the 20 V equipotential surface;

(b) E_{ρ max};

(c)
r if the charge per meter length on the inner cylinder is 20 nC/m.