The electric field outside a uniformly charged, infinite cylindrical conductor is the same as if the cylinder's charge were concentrated in a thin wire along the cylinders axis. Moreover, the potential inside a uniformly charged infinite cylindrical pipe like that inside a spherical shell is constant.
These statements are approximately true for finite cylinders and pipes as long as their length is much larger than their radius. Use these facts to calculate the capacitance of the coaxial cable arrangement.
The electric field outside a uniformly charged, infinite cylindrical conductor is the same as if the cylinder's charge were concentrated in a thin wire along the cylinders axis. Moreover, the potential inside a uniformly charged infinite cylindrical pipe like that inside a spherical shell is constant. These statements are approximately true for finite cylinders and pipes as long as their length is much larger than their radius. Use these facts to calculate the capacitance of the coaxial cable arrangement.
C=L/2kln(Ro/Ri)=2oL/ln(Ro/Ri)
If L Ro