Maximum power transfer

Objective

Show that a source delivers maximum power to the load when RL equals the source resistance.

Procedure

1. Run with RL = 100 Ω and read the power.
2. Try RL = 50, 200 and 400 Ω: all give less power.

Theory

P = V²·RL/(Rs+RL)². It peaks at RL = Rs: here 10 V behind 100 Ω gives 250 mW into 100 Ω, but only 222 mW at 50 Ω or 200 Ω.

Questions to answer

1. What is the efficiency at maximum power transfer?

Components used

Battery / DC source, 2 × Resistor 220 ohm 1/4W

About the model

Ideal wires; component models as listed in the catalogue (no parasitics, no temperature drift). Built without a breadboard so the schematic stays readable.

More Basic Electrical Lab experiments

• Wheatstone bridge
• RL circuit time constant
• AC power and power factor
• Power-factor correction
• Ohm's law