Capacitance of a cylindrical capacitor

[stosw]

Homework Statement

A coaxial cable used in a transmission line has an inner radius of 0.15 mm and an outer radius of 0.65 mm. Calculate the capacitance per meter for the cable. Assume that the space between the conductors is filled with polystyrene. (Also assume that the outer conductor is infinitesimally thin).

Homework Equations

C=\frac{2*pi*E*K}{ln(b/a)}

The Attempt at a Solution

After converting mm to m and plugging in values (used K = 2.6 for capacitance per meter) I got 551.05 pF/m.

Webassign has told me this is incorrect. Could someone point me where I went wrong?

 

[vela]

I get a completely different answer when I plug the numbers in. Try showing your work here so we can see where your error is.

 

[stosw]

Thanks.
Guess I should be more careful when using a calculator.

Correct answer is 98.596 pF/m