lumped element model

The following circuit(s) representing a lumped element equivalent of an infinitesimal sectioin of a transmission line is/are

A coaxial cable is made of two brass conductors. The spacing between the conductors is filled with Teflon $$\left( {{\varepsilon _r} = 2.1,\,\,\tan \,\,\delta = \,0} \right)$$. Whi...