3.71 In the circuit shown in Figure P3.71, $V_s$ models the
voltage produced by the generator in a power plant,
and $R_s$ models the losses in the generator, distribution
wire, and transformers. Resistances $R_1$, $R_2$, and $R_3$
model the various loads connected by a customer. How
much does the voltage across the total load change
when the customer closes switch $S_3$ and connects the
third load $R_3$ in parallel with the other two loads?
$V_s = 450 \text{ V}$ $R_s = 19 \text{ m}\Omega$
$R_1 = R_2 = 1.3 \Omega$ $R_3 = 500 \text{ m}\Omega$
