3. Coax cable A coaxial cable consists of an inner conducting wire of radius a surrounded by the \"shield\

3. Coax cable A coaxial cable consists of an inner conducting wire of radius a surrounded by the "shield" , a cylindrical conducting shell of inner radius b (i.e., b > a). The wire and shield share the same axis, thus they are "coaxial." For this problem, assume there is vacuum between the two conductors (later we'll see what the effect of an insulating material would be). (a) Calculate the capacitance of a length L of this cable, assuming L b. (b) Suppose the spacing between the conductors is very small. That is, assume b = a + d where d a. Find an approximate expression for the capacitance in terms of L, a, d, and universal constants (do not leave b in your answer). Interpret your result conceptually.