Maximum power theorem

In electrical engineering, the maximum power theorem states that for the transfer of maximum power from a source with a fixed internal resistance to a load, the resistance of the load must be the same as that of the source. This theorem is of use when driving a load such as an electric motor from a battery.

It is important to note the condition that the source resistance be fixed. If the source resistance were variable, maximum power would be transferred simply by setting the source resistance to zero.

In radio electronics there is often a requirement to match the source (e.g. transmitter) impedance to the load (e.g. antenna) impedance, but this is to avoid reflections in the transmission line. The maximum power theorem is only a part of the reason for this requirement.

The maxim is also known as Jacobi's Theorem after a Professor Jacobi of St. Petersburg in Russia, although this is also the name of an unrelated theorem in mathematics.