Finding the parallel impedance in a circuit

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Discussion Overview

The discussion revolves around finding the total impedance of a circuit with components in parallel, specifically involving complex impedances: j60 ohms, 30 ohms, -j60 ohms, and 20 ohms. Participants are attempting to resolve discrepancies in their calculations and interpretations of the circuit's behavior.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant asserts that the -j60 and j60 components should cancel each other out, leaving only the 30 ohms and 20 ohms in parallel, leading to a total impedance of 1/50.
  • Another participant provides the formula for total impedance in parallel circuits, emphasizing the need for a common denominator when adding fractions.
  • A participant questions the presence of a term "j5" in the calculations, suggesting it may be a mistake and reiterating that the j components should cancel.
  • There is a suggestion that the ratios of the components should be simplified correctly, indicating a potential misunderstanding in the representation of the fractions.

Areas of Agreement / Disagreement

Participants express differing views on whether the j components cancel out and how to correctly calculate the total impedance. The discussion remains unresolved, with multiple competing interpretations of the circuit behavior.

Contextual Notes

There are limitations in the assumptions made regarding the cancellation of j components and the addition of fractions, which may depend on the specific context of the circuit configuration.

badaboom
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Homework Statement


I need to find the total impedance in a circuit that has:
j60 ohms, 30 ohms, -j60 ohms and 20 ohms in parallel


Homework Equations


Ztotal=1/(Z1+ Z2+ Zn)


The Attempt at a Solution


I've tried doing this, but what I think is the -j60 and the j60 should cancel therefore leaving only the 30 ohms and 20 ohms in parallel, which would equal 1/50, but the answer says it is 12 ohms.

Attached is an image of the circuit and answer.
 

Attachments

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badaboom said:

Homework Statement


I need to find the total impedance in a circuit that has:
j60 ohms, 30 ohms, -j60 ohms and 20 ohms in parallel


Homework Equations


Ztotal=1/(Z1+ Z2+ Zn)


The Attempt at a Solution


I've tried doing this, but what I think is the -j60 and the j60 should cancel therefore leaving only the 30 ohms and 20 ohms in parallel, which would equal 1/50, but the answer says it is 12 ohms.

Attached is an image of the circuit and answer.

So then, 1/30 + 1/20 = 1/50 ? Check your math.
 
Parallel impedance is:

Ztotal=[1/(Z1+ Z2+ Zn)]^-1

Also remember when adding fractions you must have a common denominator.

For example 1/a + 1/b = (a+b)/ab
 
but how does that j5 get up there?
 
To be honest i think that's a mistake. The negative and positive j components cancel out. That should say 5/20 not j5/j20 even though those two ratios are equivalent.

If you're having trouble adding fractions try this page:
http://www.webmath.com/addfract.html
 

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