1. The problem statement, all variables and given/known data Coaxial cable has double layered dielectric. a=2mm, b=4mm, c=8mm, εr1=3, εr2=4.5, Uab=1000V 1. Calculate capacitance per unit length of a cable. 2. Calculate inner and outer charge densities of a cable. 2. Relevant equations Gauss law C'=Q'/U σ = nD σp = nP 3. The attempt at a solution After applying Gauss law for dielectrics, I get electric field: E=Q'/(2πε0(εr1+εr2r)). Limits of integration for voltage: (a - b) + (b - c) U=(Q'(ln(b/a)+ln(c/b)))/(2πε0(εr1+εr2)) Then, C'=(2πε0(εr1+εr2))/(ln(b/a)+ln(c/b)) This gives me C'=288pF/m but in my books solution it is C'=144pF/m. Could someone check this. Thanks for replies.