Physics help (capacitance and length) HELP PLEASE!!!?

Question

A coaxial cable has a capacitance of 3pF. The inner conductor has a radius of 1.0mm, and the outer conductor has an inner radius of 1.5mm. Find the length of the cable. (The value of epsilon not (permitivity constant) is 8.85*10^-12 )

Answer 1

Capacitance is given by:

C = Ɛ₀A / d

Since the problem asks for d (the length), then solve for it as so:

d = Ɛ₀A / C

You have two radius values, which means you must calculate the total area using the area formula for a circle.

A = πr²

Simply plug in all of the numbers and obtain the answer.