3. A long coaxial cable is made of an inner solid cylindrical rod of radius a and an outer cylindrical thin shell of radius b. The inner rod carries a uniform volume positive charge density p. The outer shell carries negative charge with a uniform surface charge density p, which is of just the right amount to make the cable as a whole electrically neutral. Find the electric field E in the regions: a) inside the inner cylinder (r< a), b) between the cylinders (a <r<b) and c) outside the cable (r> b).

Fig: 1