# Need help with superposition

Discussion in 'Homework Help' started by parabol, Mar 5, 2008.

1. ### parabol Thread Starter New Member

Mar 5, 2008
1
0
Hi all,

This is my first time posting here, and I hope I'm doing this right. But I am having quite a difficult time doing this problem. The textbook question, and my worked solution is included, if anyone could tell me where I went wrong, I would be very thankful!

The textbook states that I = 0.436A<-9.27 degrees

Thanks for the help!

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2. ### ecb123 New Member

Mar 6, 2008
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your 20+j30 are the problem in your Vab`s, you multiplied by the original values when you shoud use the series equivalent impedances you calculated for you two total z`s. The text answer is right, your numbers are all good except for your two values used.

3. ### hgmjr Moderator

Jan 28, 2005
9,030
214
What I believe ecb123 (probably emitter, collector, base, pin-1, pin-2, pin-3; his clever pneumonic for remembering the pinouts of a bjt transistor) is trying to say is that you correctly calculated the total impedance for each of the cases of the superposition solution.

Where you got off the rail was when you calculated the voltage at the node you used (20+j30) in both cases when you should have used the parallel combination of 30||(20+j30) and (40-j50)||(20+j30) respectively.

Hope I haven't succeeded in confusing you with my explanation.

hgmjr

4. ### hgmjr Moderator

Jan 28, 2005
9,030
214
parabol,

As an adjunct to my previous hint, I decided to include a Millman's Thoerem solution to your problem. This provides an independent verification of the answer which you included in your original posting of the circuit.

hgmjr

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