A two-port network shown below is excited by external dc sources. The voltages and the currents are measured with voltmeters $${V_1}$$, $${V_2}$$ and ammeter $${A_1}$$, $${A_2}$$ (all assumed to be ideal), as indicated. Under following switch conditions, the readings obtained are:

(i) $${S_1} - open,\,\,\,\,{S_2} - closed$$
$${A_1} = 0\,A,\,\,\,\,\,\,{V_1} = \,4.5\,\,V,$$
$${V_2}\, = \,1.5\,V,\,\,\,\,{A_2}\, = \,1\,A$$

(ii) $${S_1} - Closed,\,\,\,\,{S_2} - Open$$
$${A_1} = 4\,A,\,\,\,\,\,\,{V_1} = \,6\,\,V,$$
$${V_2}\, = \,6\,V,\,\,\,\,{A_2}\, = \,0\,A$$

The z-parameter matrix for this network is

In the two port network shown in the figure below, z₁₂ and z₂₁ are, respectively

A two-port network is represented by ABCD parameters given by $$\left[ {\matrix{ {{V_1}} \cr {{I_1}} \cr } } \right] = \,\left[ {\matrix{ A & B \cr C & D \cr } } \right]\,\left[ {\matrix{ {{V_2}} \cr { - \,{I_2}} \cr } } \right]$$

If port-2 is terminated by $${R_L}$$, the input impedance seen at port-1 is given by

If R₁ = R₂ = R₄ = R and R₃ = 1.1R in the bridge circuit shown in figure, then the reading in the ideal voltmeter connected between a and b is