Calculating Thevenin Resistance and Current in a Complex Circuit

In summary, the problem involves finding the current in R1 using Thevenin's Theorem. After calculating the voltages at the points where R1 is removed and the Thevenin resistance, the current in R1 is found to be 1.2096A, which is slightly different from the expected value of 1.22003A. The discrepancy may be due to rounding errors or a mistake in evaluating the Thevenin resistance.
  • #1
whoareyou
162
2

Homework Statement



The circuit looks like this: http://i.imgur.com/QtgiCdR.png

R1= 10 Ω
R2= 8 Ω
R3= 3 Ω
R4= 5 Ω
R5= 2 Ω

V= 15 V

I'm trying the find the current in R1 by using Thevenin's Theorem.

Homework Equations



Basic Circuit Analysis Formulas

The Attempt at a Solution



So I calculated the voltages at the points where R1 is removed. 15V on the left side and 90/101V on the right side (confirmed by LTspice). Then I tried to calculate the Thevenin resistance which (once the voltage source is shorted) is the R2 || R3 || (R4 + R5) which turns out to be 168/101Ω. So putting everything together now, Vth = 15 - 90/101 and Rth = 168/101 and Rl = 10, I get that the current in R1 is 1.2096A but according to LTspice, it should be 1.22003A. What am I doing wrong?
 
Physics news on Phys.org
  • #2
Rounding error?
With Kirchhoff's laws, I get 270/73 V and 1635/584 V for the voltages at the two points (relative to negative source connection, first value at resistors 2/3/4) and 1425/1168 A which is about 1.220034 A as current through R1.
 
  • #3
Check your evaluation of Rth. Note that R4 and R5 are not in series in this case, since their junction feeds the load terminal.
 

1. What is Thevenin's Theorem?

Thevenin's Theorem is a fundamental concept in electrical engineering that states that any linear electrical network with multiple resistive elements and sources can be simplified into an equivalent circuit with just one voltage source in series with one resistor.

2. How is Thevenin's Theorem used in circuit analysis?

Thevenin's Theorem is used to simplify complex circuits into a simpler equivalent circuit, making it easier to analyze and calculate values such as voltage, current, and power. It is often used in conjunction with other circuit analysis methods, such as Kirchhoff's Laws.

3. What are the steps to find the Thevenin equivalent circuit?

There are three main steps to find the Thevenin equivalent circuit. First, remove the load from the original circuit and determine the open circuit voltage (Voc) at the load terminals. Then, determine the equivalent resistance (Req) by shorting all voltage sources and opening all current sources in the original circuit, and calculating the resistance between the load terminals. Finally, draw the Thevenin equivalent circuit with the voltage source (Voc) in series with the equivalent resistance (Req).

4. What is the difference between Thevenin and Norton equivalent circuits?

Thevenin and Norton equivalent circuits are both simplifications of complex circuits, but they differ in the type of source used. Thevenin equivalent circuits use a voltage source in series with a resistor, while Norton equivalent circuits use a current source in parallel with a resistor. They are equivalent in that they produce the same voltage and current values at the load terminals.

5. Can Thevenin's Theorem be applied to non-linear circuits?

No, Thevenin's Theorem can only be applied to linear circuits, which are circuits where the relationship between voltage and current remains constant. Non-linear elements, such as diodes and transistors, do not follow this relationship and therefore cannot be simplified using Thevenin's Theorem.

Similar threads

How to find the equivalent resistance of this electric circuit?
    • Engineering and Comp Sci Homework Help
Replies
5
Views
3K
Engineering Solving circuit with Thevenin's theorem
    • Engineering and Comp Sci Homework Help
Replies
4
Views
2K
Engineering How do I find Vth with the node voltage method?
    • Engineering and Comp Sci Homework Help
Replies
10
Views
2K
Engineering Why is the output voltage of the subtractor calculated like this?
    • Engineering and Comp Sci Homework Help
Replies
5
Views
882
Calculate voltage over capacitor and resistance
    • Introductory Physics Homework Help
Replies
7
Views
207
Engineering AC Circuit Phasors: Find I1, I2, I3
    • Engineering and Comp Sci Homework Help
Replies
26
Views
2K
Engineering How to Calculate Thevenin Equivalent Circuit
    • Engineering and Comp Sci Homework Help
Replies
5
Views
1K
Engineering Why are the voltages calculated in this way? (CE BJT Amp circuit)
    • Engineering and Comp Sci Homework Help
Replies
8
Views
1K
Engineering Finding the Thevenin Equivalent Circuit for a Complex Network
    • Engineering and Comp Sci Homework Help
Replies
22
Views
2K
Engineering Solve Superposition Theorem for R1, R2 Circuit
    • Engineering and Comp Sci Homework Help
Replies
18
Views
2K

Hot Threads

Recent Insights

Back
Top