# Homework Help: Thevenin voltage and impedance

1. Jan 28, 2016

### crom1

1. The problem statement, all variables and given/known data
Find the maximum power on a impedance Z.

2. Relevant equations

3. The attempt at a solution
I got as Thevenin impedance Zt=4+j4 and Ut= 32 V, but since my solution for power is wrong, something is wrong with either impedance or voltage (or both).
If point A is above Z, and point B is under Z, looking from A to B I get for impedance:
First j4 , then since I have current source in of the branches, I ignore impedances in that branch and get j4+(j4-j4+4) and since there is voltage source I ignore 2-j12.
For Thevenin voltage, I tried with superposition, and if potential of B=0, I get that for A:
$$\varphi_A= 16 \angle 0 + 4 \angle 0 \cdot 4 + 4 \angle 0 \cdot j4 + 4 \angle 0 \cdot (-j4)=32$$

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2. Jan 28, 2016

### Staff: Mentor

Your Thevenin values look okay. How did you calculate the maximum power?

3. Jan 29, 2016

### crom1

I=Ut/(Z+Zt)=2-j2 , P=I^2 Z = 32-32i = 32 sqrt(2) , And the solution says 64.

4. Jan 29, 2016

### Staff: Mentor

What value did you give to the load impedance Z?

5. Jan 29, 2016

### crom1

Z=Zt=4+j4

6. Jan 29, 2016

### Staff: Mentor

Check the maximum power theorem for complex impedance. I think you'll find that the imaginary part of the load should nullify the source impedance's imaginary component.

7. Jan 29, 2016

### crom1

You're right. I now get P=64-j64, do I now just take real part to get P=64?

8. Jan 29, 2016

Yup.