I've got this simple exercise about maximum power transfer.


simulate this circuit – Schematic created using CircuitLab

Where \$E_{th}=100\angle 0º \$ [V] and \$Z_{th}=100\angle 20º \$.

Then I completed this table with values I obtained after solving the equations on \$Mathematica\$.

enter image description here

I know that the theorem states that the maximum power transfer on the load will be when \$R_{L}=R_{eq}\$ and \$X_{L}=-X_{eq}\$ . This agrees with the values of \$P_L\$ .

The efficiency is bugging me. How is it the same efficiency with the first 2 values? and is it true that the efficiency isn't the best at the maximum power transfer load values?

Are my calculations wrong or is it something else?

Thank you!


1 Answer 1


Your results are correct.

MPT is always 50% efficiency for this circuit when (the load=) "conjugate Zl" is matched to source.

It is also 50% efficient when the Real part of Z ( load )is matched to source.

  • 1
    \$\begingroup\$ which Z? --- Zl ? \$\endgroup\$ May 17, 2019 at 3:04

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