1.E = λ / (2π ε0 r) = 18*10^(-9) / (2π *8.85*10^(-12)*0.06) = 5395.08 V/m
方向：长直导线AB带正电时向外,带负电时向里.
2.U(0.20) = 2*10^(-8) / (4π *8.85*10^(-12)*0.10) + 4*10^(-8) / (4π *8.85*10^(-12)*0.30) = 2997.27 V
U(0.50) = 2*10^(-8) / (4π *8.85*10^(-12)*0.50) + 4*10^(-8) / (4π *8.85*10^(-12)*0.50) = 1079.02 V