Source Resistance Output Three-Row Scan - Electronic Circuits III: Comparators and Interfaces Step by Step

A loaded source must show how source resistance moves voltage from the load into the internal resistor. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

A loaded source is a divider, not an ideal rail

The source voltage and load stay fixed. Increasing source resistance moves more voltage into the source resistor and less onto the load.

I=\frac{V_s}{R_s+R_L}

Three source resistances show the voltage trade

The current, source drop, and load voltage are computed from the same row. The two voltage drops add back to the same battery each time.

\begin{array}{c|c|c|c|c}R_s&R_L&I&V_{R_s}&V_L\\2\ \text{ohm}&4\ \text{ohm}&2\ \text{A}&4\ \text{V}&8\ \text{V}\\4\ \text{ohm}&4\ \text{ohm}&\tfrac{3}{2}\ \text{A}&6\ \text{V}&6\ \text{V}\\8\ \text{ohm}&4\ \text{ohm}&1\ \text{A}&8\ \text{V}&4\ \text{V}\\\end{array}

The stiff row holds more load voltage

The low source-resistance row leaves 8 volts on the load. The high source-resistance row leaves 4 volts.

8\ \text{V}>4\ \text{V}

The divider scan prevents a vague strength claim

A source is called stiff here only because the exact divider row shows a smaller internal drop. No frequency response or active current limit is being claimed.

6\ \text{V}+6\ \text{V}=12\ \text{V}