The characteristic impedance of a co-axial cableis of the order of:

Explanation

(a) The characteristic impendance `Z=sqrt(L//C)L=(Z^(2))(C)=(50)^(2)(20xx10^(-12))H=0.05H`.
(b) The characteristic impedance of a trasnmission line is the impedance that an infinite length of line would present to a power supply at the input end of the line. Thus, `Z_(oo)=Z_(0)=50Omega`.