Given that k_e = k_e_1 for a lessthanorequalto rho < rho_0 k_e = k_e_2 for rho_0 lessthanorequalto rho < b V_a = Q/2 pi epsilon_0 L k_e_1 ln rho_0/2 V_b = Q/2 pi epsilon_0 L k_e_2 ln rho_0/b V_ab = V_a - V_b = Q/2 pi epsion_0 L [1/k_e_1 ln rho_0/a - 1/k_e_2 ln rho_0/b] C = Q/V_a times b = 2 pi epsilon_0 L/[1/k_e_1 ln[rho_0/a] - 1/k_e_2 ln[rho_0/b)]