Load Resistance Output Three-Row Scan - Electronic Circuits II & III: Decision Networks and Interfaces Step by Step

A load-resistance scan shows how an interface output trades load voltage, current, and power when the source resistance is not zero. The rows are exact only for the declared source voltage, source resistance, load resistance, ideal wires, and steady linear load model; real interfaces add component tolerance, contact resistance, nonlinear loads, self-heating, bandwidth limits, temperature drift, and voltage/current/power measurement uncertainty.

A load scan must keep voltage, current, and power together instead of reading any one column in isolation. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Changing load resistance changes both current and voltage

The source resistance is fixed, so a heavier load pulls more current and loses more voltage inside the source.

I=\frac{V_s}{R_s+R_L},\quad P_L=V_L I

Three load rows separate heavy and light loads

The table does not assume that higher load resistance means lower load voltage. It computes the current first, then the load voltage and power.

\begin{array}{c|c|c|c|c}R_s&R_L&I&V_L&P_L\\2\ \text{ohm}&2\ \text{ohm}&3\ \text{A}&6\ \text{V}&18\ \text{W}\\2\ \text{ohm}&4\ \text{ohm}&2\ \text{A}&8\ \text{V}&16\ \text{W}\\2\ \text{ohm}&10\ \text{ohm}&1\ \text{A}&10\ \text{V}&10\ \text{W}\\\end{array}

The light load keeps more voltage but less current

The light row leaves 10 volts on the load, but its current is only 1 ampere.

10\ \text{V}\quad1\ \text{A}

Load power needs both columns

The heavy row has more current, while the light row has more voltage. The power column is why both facts must stay visible.

18\ \text{W}\quad10\ \text{W}