# "Thevenin, Norton, and Maximum Power" worksheet

#### acalhoon

Joined May 14, 2013
2
I've only just gone through a handful of the questions in the "Thevenin's, Norton's, and Maximum Power Transfer Theorems" worksheet (http://www.allaboutcircuits.com/worksheets/thev.html) I'm fairly confident the Thevenin series resistance is incorrect for question 8. The revealed answers show:
Vth = 8.77 V
Rth = 210.53 ohm

Calculations for Thevenin equivalent voltage:
R1 = 300 ohm
R2 = 1000 ohm
R3 = 2000 ohm
R4 = 400 ohm

Vth = I2 * R3
I1(R1 + R2) - I2(R2) = 15
-I1(R2) + I2(R2 + R3 + R4) = 0

I1 = 271/14820 A
I2 = 1/228 A
Vth = 2000/228 = 8.77V

Calculations for Thevenin equivalent resistance (Looking in method):
((R1 || R2) + R4) || R3 = 479.5 ohm

Calculations for Thevenin equivalent resistance (Short circuit current method):
Ith = I2
I1(R1 + R2) - I2(R2) = 15
-I1(R2) + I2(R2 + R4) = 0

I1 = 21/280
I2 = 3/164

Rth = Vth/Ith
Rth = 2000/228*164/3 = 479.5 ohm

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#### acalhoon

Joined May 14, 2013
2
Another issue:

The "note" associated with the answer for question 11 reads:
"Let students know that there really is such a thing as a perfect current source, just as there is no such thing as a perfect voltage source. However, there are devices the closely approximate ideal current sources (current transformers in AC circuits and "current mirror" DC transistor circuits, for example)."
"Let students know that there really is no such thing as a perfect current source, just as there is no such thing as a perfect voltage source. However, there are devices the closely approximate ideal current sources (current transformers in AC circuits and "current mirror" DC transistor circuits, for example)."

#### Georacer

Joined Nov 25, 2009
5,182
Thank you, acalhoon.

I, myself solved the exercise and initially made the same mistake as the author. That is, to first solve for the Thevenin voltage, and then use the same transformed circuit to find the resistance, not noticing that the merged resistances where unusable.

I would also add, for Question 8, that it should read "Find the Thevenin equivalent circuit" instead of "Thevenize".