$($a$)$ Can we connect two different magnitude voltage sources in parallel? Support your answer.

$($b$)$ A voltmeter is used to measure Vo in the circuit in Fig. $2\mathrm{.}1.$ The voltmeter model consists of an ideal voltmeter in parallel with a $250-k$ resistor. Let $Vs=95V,Rs=25k,$ and $R_1=40k.$ Analyze the circuit to find out $Vo$ with and without the voltmeter when

$($i$)R_2=5k$

$($ii$)R_2=25k$

$($iii$)R_2=250k$

$($c$)$ As a design engineer, you are asked to design a lighting system consisting of a $70-$W power supply and two light bulbs as shown in Fig. $2\mathrm{.}2.$ You must select the two bulbs from the following three available bulbs.

$R1=80,cost=$$$0\mathrm{.}60($ standard size $)$

$R2=90,cost=$$$0\mathrm{.}90($ standard size $)$

$R3=100,cost=$$$0\mathrm{.}75($ nonstandard size $)$

The system should be designed for minimum cost such that I lies within the range $I=1\mathrm{.}2A+-5$ percent.