Question

A cylindrical capacitor has two coaxial cylinders of length 20 cm and radii 2r and r. Inn

Answer 1

your question is incomplete. A complete question is -----> A cylindrical capacitor has two coaxial cylinders of length 20 cm and radii 2r and r. find capacity of capacitance ?

we know, capacity of capacitance of the given system is given by , $\mathbb{C}=\frac{2\pi\epsilon_0l}{2.303log_{10}\left(\frac{b}{a}\right)}$

where l is length of cylinderical capacitor.
b is outer radius of coaxial cylinder
a is inner radius of coaxial cylinder.

now, $\mathbb{C}=\frac{2\pi\epsilon_0\times0.2}{2.303log_{10}\frac{2r}{r}}$

= $\frac{0.4\pi\epsilon_0}{ln2}$

hence, capacity of capacitance is $\frac{0.4\pi\epsilon_0}{ln2}$