Thevenin resistance and Thevenin voltage confusion

Click For Summary

Discussion Overview

The discussion centers around confusion regarding the calculation of Thevenin resistance (RTh) and Thevenin voltage in a circuit analysis context. Participants are addressing numerical errors, simulation discrepancies, and definitions related to Thevenin's theorem, with a focus on both theoretical and practical aspects of circuit analysis.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant claims that a numerical expression for RTh is incorrect, stating that Ohms times Ohms results in Ohms2.
  • Another participant suggests that the numerical error should only affect the result by a power of ten, but notes that simulation results are significantly off.
  • It is proposed that the Thevenin resistance should exceed 1000 Ω, given that one resistor in the circuit is already 1000 Ω, indicating a need to verify calculations.
  • A participant provides an alternative method for determining Thevenin voltage and resistance using a "black box" approach, emphasizing that this method applies to linear and passive circuits.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the correct calculation of Thevenin resistance and voltage, with multiple viewpoints and unresolved confusion remaining in the discussion.

Contextual Notes

Some limitations include potential missing assumptions in the calculations, the dependence on circuit definitions, and the applicability of the proposed methods to specific types of circuits.

theycallmevirgo
Messages
108
Reaction score
25
Homework Statement
Use Thevenin Equivalent Circuit to find current through R_L
Relevant Equations
E_Th=open circuit voltage

R_Th=R_t looking into the circucit from the load
1577480955132.png


1577480981169.png
 
Physics news on Phys.org
Your numerical expression for ##R_{Th}## is not correct. ##1000 \Omega \cdot 690 \Omega## is not ##690 k\Omega##. Ohms times Ohms is Ohms2.
 
Ok, but that should only throw me off by a power of 10. The simulation results aren't even close.
 
Well, your Thevenin resistance should be greater than 1000 Ω(since R4 is already 1000 Ω), right? So check your math.
 
A slightly different definition (with the same answers); the "black box" approach:
1) Measure (or calculate) the open circuit voltage on the output terminals (i.e. RL = ∞ in your schematic). This is the Thevenin voltage.
2) Measure (or calculate) the short circuit current from the output terminals (i.e. RL = 0 in your schematic). Divide the open circuit voltage by the short circuit current to get the Thevenin resistance.

Of course this only works for circuits that are linear and passive.
 

Similar threads

Thevenin Theorum
  • · Replies 1 ·
Replies
1
Views
2K
Engineering How do I find Vth with the node voltage method?
  • · Replies 10 ·
Replies
10
Views
4K
Why is the Thevenin resistance in this problem 3.2 kΩ?
  • · Replies 17 ·
Replies
17
Views
3K
Are Overly Complicated Homework Problems Beneficial for Student Learning?
  • · Replies 2 ·
Replies
2
Views
2K
Engineering How to Calculate Thevenin Equivalent Circuit
  • · Replies 5 ·
Replies
5
Views
3K
Engineering Find the Thevenin equivalent circuit
  • · Replies 42 ·
2
Replies
42
Views
7K
Calculating the Thevenin's Resistance of a Breadboarded Circuit
  • · Replies 9 ·
Replies
9
Views
2K
I finding the Thevenin equivalent resistance
  • · Replies 6 ·
Replies
6
Views
2K
Engineering Finding the Thevenin Equivalent Circuit for a Network with a Load Resistor
  • · Replies 1 ·
Replies
1
Views
2K
Engineering Finding Thevenin Equivalent Voltage for a Circuit with Multiple Voltage Sources
  • · Replies 12 ·
Replies
12
Views
3K