Superposition calculation for a circuit

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Discussion Overview

The discussion revolves around a superposition calculation for an electrical circuit, specifically focusing on the application of superposition in determining load current. Participants are examining the calculations related to impedance and current through the load, referencing a textbook for guidance.

Discussion Character

  • Homework-related, Technical explanation, Debate/contested

Main Points Raised

  • One participant believes their approach to the superposition problem is correct and expects to obtain the same answer as from Thevenin's theorem, but notes a discrepancy in the load current.
  • Another participant disagrees with the net impedance value calculated by the first participant, specifically questioning the imaginary component and suggesting an error in handling the complex fraction.
  • A third participant expresses frustration over small mistakes and lack of confidence, indicating they have made corrections to their calculations based on feedback received.
  • There is a discussion about the correct manipulation of terms in the calculations, with one participant pointing out that adding certain terms at a specific point in the calculation is incorrect due to differing denominators.
  • The first participant acknowledges the feedback and indicates they will redo their calculations.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are disagreements regarding the calculations and interpretations of the impedance values. Multiple competing views remain on the correctness of the approach and specific steps taken in the calculations.

Contextual Notes

Limitations include potential missing assumptions in the calculations, dependence on the definitions of impedance and complex numbers, and unresolved steps in the mathematical process.

billyray
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Homework Statement


I have tried to answer the superposition question in the included file. I have gone through the workings as the same as in my john bird electrical book. I believe I have done nothing wrong in my approach and should be getting the same answer as my thevenins answer. the current through the load is completely different though

Homework Equations


total impedance when v2 removed = j4 in series with parallel j6 and 35 + j 35 .71
v1 removed total impedance j6 in series with parallel j4 and 35 + j35.71
then volts over resistances to find I then use the currents to find load current adding i2 and i5.
i1 x j6/j6 + 35 + j 35.71 = I2
i4 x j4/j4 + 35 + j35.71 = 1 5

i5 + i2 = I load

The Attempt at a Solution


it is included in file
I have added my attemp
 

Attachments

Last edited by a moderator:
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Hi billyray,

Welcome to Physics Forums!

I've just taken a look at your work for the first part where you've suppressed the V2 source, and I find that I don't agree with your net impedance value. In particular, the imaginary component looks incorrect to me. I think things started to go off the rails when you were dealing with the numerator during the normalization of the complex fraction. This is the bit I'm referring to:

upload_2017-11-21_9-42-0.png
 

Attachments

  • upload_2017-11-21_9-42-0.png
    upload_2017-11-21_9-42-0.png
    15.2 KB · Views: 526
hi Gniell
Thank you so much for listening. I am trying very hard and small mistakes and lack of confidence is frustrating me. I have studied a lot for this and thought I could do it. I have changed the numerator as I see I did not add j4 do you think it is more wrong than this?. I have attached my correction.
 

Attachments

I then multiplied by the conjugate of the denominator that was 35- j35.71
 
You're good until the last two lines. You can't add the j4 to the numerator at that point: it's a separate term with a different denominator.
 
Thanks gneill
i will redo
 

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