P 7.9 ~J ( r = a, t = ε0 g ) = g ε0 e−1 a3 3r2 P 7.11 R = 1 2πg ( 1 a1 + 1 a2 − 2 L ) P 7.12 a) ~J = V0g1g2 r(g1 ln(c/b)+g2 ln(b/a)) r̂, ~E =  V0g2 r(g1 ln(c/b)+g2 ln(b/a)) r̂ a < r < b V0g1 r(g1 ln(c/b)+g2 ln(b/a)) r̂ b < r < c b) σ(r = a) = 2πLV0g2 (g1 ln(c/b)+g2 ln(b/a)) , σ(r = c) = − 2πLV0g1 (g1 ln(c/b)+g2 ln(b/a)) c) I = 2πLV0g1g2 g1 ln(c/b)+g2 ln(b/a) d) R = 1 2πL ( ln(c/b) g2 + ln(b/a) g1 ) e) RL = 1 2πL ( ln(c/b) g2 + ln(b/a) g1 ) , P = V 2 0 πLg1g2 2(g1 ln(c/b)+g2 ln(b/a))