A coaxial cable is made of two brass conductors. The spacing between the conductors is filled with Teflon $$\left( {{\varepsilon _r} = 2.1,\,\,\tan \,\,\delta = \,0} \right)$$. Which one of the following circuits can represent the lumped element model of a small piece of this cable having length $$\Delta \,\,z\,\,?$$

The directivity of an antenna array can be increased by adding more antenna elements, as a larger number of elements

A 200 m long transmission line having parameters shown in the figure is terminated into a load ܴ$$R_L$$. The line is connected to a 400 V source having source resistance $$R_S$$ through a switch, which is closed at t = 0. The transient response of the circuit at the input of the line (z = 0) is also drawn in the figure. The value of ܴ$$R_L$$ (in $$\Omega $$ ) is ___________.

A coaxial capacitor of inner radius 1 mm and outer radius 5 mm has a capacitance per unit length of 172 pF/m. If the ratio of outer radius to inner is doubled, the capacitance per unit length (in pF/m) is _____.