What is the capacitance of this cable? What is the potential difference?

Question

Part 1:

A 50 m length of coaxial cable has a solid cylindrical wire inner conductor with a diameter of 2.681 mm and carries a charge of 7.91 micro C. The surrounding conductor is a

cylindrical shell and has an inner diameter of 9.103 mm and a charge of -7.91 micro C.

Assume the region between the conductors is air. The Coulomb constant is 8.98755 £ 9 N m2/C2.

What is the capacitance of this cable? Anwer in units of nF.

Part 2:

What is the potential difference between the two conductors? Answer in units of kV.

Answer 1

1. C/L = 2pi*Kd*e0/(ln(R1/R2)) = 4.5510355E-11 F/m (see ref.)

C = 50*C/L = 2.2755E-9 F

2. V = Q/C = 3476.13 V