% Fixed geometry for coax
a = 2;
b = 5;
Vab = 10;
e0 = 8.85e-12;


% Potential between cylinders
V = @(r) (Vab*(1/r - 1/b))./(1/a - 1/b)

We = (Vab^2*pi*e0)./(a*(1/a-1/b))

Q = (Vab/a)*((2*pi*e0)/(1/a-1/b))

% Capacitance per length ( C/L )
C_L = @(b) (2*pi*e0)./(a*(1/a - 1./b))

% C/L values from COMSOL
% a = 2
% b = [5 7 9]
C_L_COMSOL_Q  = [9.1673E-11 7.6984E-11 7.0645E-11] 
C_L_COMSOL_We = [9.2722E-11 7.7887E-11 7.1531E-11]

figure 
hold on
i = 1
for k = [5 7 9]
    plot(k, C_L(k), 'o')
    plot(k, C_L_COMSOL_Q(i), '*')
    plot(k, C_L_COMSOL_We(i), 's')
    i = i+1;
end
legend('Theoretical', 'COMSOL_Q', 'COMSOL_{We}');
