How can I proceed to solve this exercise? I know that pMAX= |VTh|^2 / 8 * RTh

I tried to calculate the Thevenin Resistance, but I didn't manage to do it, because I can't put together anything in parallel or in series so I really don't know how to find it here.

For the Thevenin Voltage I have the same problem, I don't know which "tactics" I could use here to find the voltage.

Image of the exercise text and diagram

  • \$\begingroup\$ You need to tag this as homework. Then search web for something like this. \$\endgroup\$ Nov 10, 2020 at 19:35
  • \$\begingroup\$ @relayman357 sorry I didn't know I had to tag as homework, anyway i know the formula of the maximum power transfer but I dont know how to find the Thevenin Voltage \$\endgroup\$
    – user266743
    Nov 10, 2020 at 19:39

1 Answer 1


To find the Thévenin voltage, Vth, take ZL out and then find the voltage that is developed between A & B due to your source (where A & B are the terminals of ZL in your drawing). Vth is also known as the "open circuit" voltage.

To find the Thévenin impedance, Zth, kill the source, remove ZL, and then find the equivalent impedance between points A & B.

Read about Thévenin here.

enter image description here

  • \$\begingroup\$ That's what I have been trying to do but I can't find the voltage between A and B, the circuit is too complicated for me \$\endgroup\$
    – user266743
    Nov 10, 2020 at 19:58
  • \$\begingroup\$ If ZL is removed and the source is killed (by opening since it is a current source) then you should be able to see it clearer. You may need to redraw it to help, that never hurts. You should see that the upper 2 components are in series (Zup = 30-j10). Likewise, the lower 2 components are also in series (Zlow = 40+j20). Now, you should see that the equivalent impedance between points A & B will be Zup in parallel with Zlow. That will be your resulting Zth. \$\endgroup\$ Nov 10, 2020 at 20:03
  • \$\begingroup\$ Ok for the impedence I found it and it's 20.6 + j 4.2 but the problem for me is to find the Vth how can i do that? \$\endgroup\$
    – user266743
    Nov 10, 2020 at 20:08
  • \$\begingroup\$ Recheck your math on how to calculate equivalent impedance of two parallel impedances (your answer above is wrong). Then, using the circuit i added to my answer, use KVL around any convenient loop to find VTH. \$\endgroup\$ Nov 10, 2020 at 20:16
  • \$\begingroup\$ Thanks ok I will do that, probably is miscalculated the Rth \$\endgroup\$
    – user266743
    Nov 10, 2020 at 20:57

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