Circuit reduction/Thevenin's equvalent resistance question.

  • Context: Engineering 
  • Thread starter Thread starter braceman
  • Start date Start date
  • Tags Tags
    Circuit Resistance
Click For Summary

Discussion Overview

The discussion revolves around finding the Thevenin equivalent resistance (Zth) of a given circuit. Participants are exploring methods to reduce the circuit and clarify the process of determining Zth, with a focus on impedance and circuit configuration. The conversation includes elements of homework assistance and technical reasoning.

Discussion Character

  • Homework-related
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant expresses difficulty in reducing the circuit to find Zth, noting conflicting advice from different sources about whether to analyze the circuit from the terminals or from the input side.
  • Another participant requests a clearer circuit diagram, indicating issues with the format of the original attachment.
  • A participant suggests that the top and bottom rails of the circuit can be treated as a single node, proposing a method to simplify the circuit by "folding" it along a central line.
  • Subsequent replies discuss steps to reduce parallel resistor pairs and combine resistors to find the final impedance, with one participant outlining a specific approach to achieve Zth.
  • Mathematical expressions for combining resistances are presented, with participants calculating values for Zth using the formula for resistors in parallel.
  • There are multiple calculations provided, with participants sharing their results and expressing tentative agreement on the final value of Zth.

Areas of Agreement / Disagreement

Participants generally agree on the steps to reduce the circuit and the formulas to use, but there is no consensus on the final value of Zth, as calculations vary among participants.

Contextual Notes

Some calculations presented rely on specific assumptions about the circuit configuration, and there may be unresolved steps in the mathematical reasoning. The discussion reflects varying levels of familiarity with circuit reduction techniques.

braceman
Messages
30
Reaction score
0

Homework Statement



I have a question to find the thevenin equivalent of a circuit (attached). I have found the Vout but am struggling when trying to reduce the circuit to just the Zth value. All the examples I have don't show an impedance between the terminals and I can't find any examples to try and follow through on how to reduce it. it doesn't help that I've got one book saying look at the circuit from the terminals side, and another saying work FROM the other side (where the Vin was and is now short-circuited) towards the terminals. This configuration is proving problematic for me.

Homework Equations



Resistance series and parallel equations.

Re = R1+R2 etc...Re = R1R2/R1+R2

The Attempt at a Solution



I want to work this one out myself and don't want the answer (no point in blagging it if I can't do it again in the future!) but need some pointers.
Can anyone talk me through how to reduce a circuit like this or point me to a webby with some good examples. I've seen a suggestion to use the left hand side in a 'star' config and convert it to a 'delta', but my books haven't covered these so I'm guessing there's another normal way to do it. I'm betting it's just staring me in the face, but I haven't done this type of thing for a good few years. Any pointers would be greatly appreciated!
 

Attachments

Last edited:
Physics news on Phys.org
Can you post your circuit diagram as a gif or jpg? My (ancient, creaking) software can't sort out the format of your .docx.doc attachment, and I'm always leery of opening an unknown file with an application that has enough smarts to read/write my hard disk and run macros...
 
is this pic any good for you?
 

Attachments

  • circuit1.jpg
    circuit1.jpg
    18 KB · Views: 465
braceman said:
is this pic any good for you?
Much better, thanks. I'll take a look...

...Looks like the top rail and bottom rail are connected by the wire on the far left. That makes the top and bottom a single node, and you can move the connections all to one rail (the equivalent of "folding" the circuit along the central line). Does that help you out?
 
Last edited:
hopefully this is close...If it is, then next step would be to reduce the 2 parallel resistor pairs.

Then add the left and top middle resistors to make a single resistor, which would then sit in parallel with the final right resistor,,,and this would give us the final resistance (impedance) for Zth??
 

Attachments

  • circuit2.jpg
    circuit2.jpg
    16.6 KB · Views: 434
braceman said:
hopefully this is close...


If it is, then next step would be to reduce the 2 parallel resistor pairs.

Then add the left and top middle resistors to make a single resistor, which would then sit in parallel with the final right resistor,,,and this would give us the final resistance (impedance) for Zth??

Sounds like an excellent plan :smile:
 
R1R2/R1+R2 = (2 x 10/7)/2+10/7 = 5/6
 

Attachments

  • circuit3.jpg
    circuit3.jpg
    17.6 KB · Views: 477
R1+r2 = 5/6 + 5/2 = 10/3
 

Attachments

  • circuit4.jpg
    circuit4.jpg
    17.9 KB · Views: 442
R1R2/R1+R2 = (10Z/3 x 5Z/6) / (10Z/3 + 5Z/6) = 2Z/3

Therefore Zth - 2Z/3 (hopefully!)
 
  • #10
braceman said:
R1R2/R1+R2 = (10Z/3 x 5Z/6) / (10Z/3 + 5Z/6) = 2Z/3

Therefore Zth - 2Z/3 (hopefully!)

Yup. Looks good.
 
  • Like
Likes   Reactions: 1 person

Similar threads

Engineering How to Calculate Thevenin Equivalent Circuit
  • · Replies 5 ·
Replies
5
Views
3K
Calculating the Thevenin's Resistance of a Breadboarded Circuit
  • · Replies 9 ·
Replies
9
Views
2K
Engineering Find the Thevenin equivalent circuit
  • · Replies 42 ·
2
Replies
42
Views
7K
Engineering How do I find Vth with the node voltage method?
  • · Replies 10 ·
Replies
10
Views
4K
Engineering Why are the voltages calculated in this way? (CE BJT Amp circuit)
  • · Replies 8 ·
Replies
8
Views
2K
Engineering Create a circuit in simulation to prove my work (2 batteries and 1 lamp bulb)
  • · Replies 5 ·
Replies
5
Views
2K
Engineering How to determine circuit components of ´Mystery Box’ ?
  • · Replies 4 ·
Replies
4
Views
2K
I finding the Thevenin equivalent resistance
  • · Replies 6 ·
Replies
6
Views
2K
Engineering Transform question about this circuit
  • · Replies 4 ·
Replies
4
Views
2K
Engineering Thevenin's equvalent circuit of the network?
  • · Replies 2 ·
Replies
2
Views
2K