# What is Thevenin's theorem: Definition and 53 Discussions

As originally stated in terms of direct-current resistive circuits only, Thévenin's theorem states that, "For any linear electrical network containing only voltage sources, current sources and resistances can be replaced at terminals A-B by an equivalent combination of a voltage source Vth in a series connection with a resistance Rth."

The equivalent voltage Vth is the voltage obtained at terminals A-B of the network with terminals A-B open circuited.
The equivalent resistance Rth is the resistance that the circuit between terminals A and B would have if all ideal voltage sources in the circuit were replaced by a short circuit and all ideal current sources were replaced by an open circuit.
If terminals A and B are connected to one another, the current flowing from A to B will be Vth/Rth. This means that Rth could alternatively be calculated as Vth divided by the short-circuit current between A and B when they are connected together.In circuit theory terms, the theorem allows any one-port network to be reduced to a single voltage source and a single impedance.
The theorem also applies to frequency domain AC circuits consisting of reactive and resistive impedances. It means the theorem applies for AC in an exactly same way to DC except that resistances are generalized to impedances.
The theorem was independently derived in 1853 by the German scientist Hermann von Helmholtz and in 1883 by Léon Charles Thévenin (1857–1926), an electrical engineer with France's national Postes et Télégraphes telecommunications organization.Thévenin's theorem and its dual, Norton's theorem, are widely used to make circuit analysis simpler and to study a circuit's initial-condition and steady-state response. Thévenin's theorem can be used to convert any circuit's sources and impedances to a Thévenin equivalent; use of the theorem may in some cases be more convenient than use of Kirchhoff's circuit laws.

View More On Wikipedia.org
1. ### Engineering How do I find Vth with the node voltage method?

Hello. I'am practicing circuit analisis about the norton and thevenin's circuits and I can't seem to manage to get the right thevenin's voltage using the node voltage for a) resolution 1) I did source transformation turning the current source(2A) into a voltage source (10V) applied node voltage...
2. ### Engineering Applying Thevenin's theorem to AC circuits

So I've seen other threads on here with the same problem from a few years ago, and I'm just not getting the same answers. However, I followed along with a similar problem in the textbook and used all the same methods, so can't understand where I've gone wrong, or if I even am wrong. Also not...
3. ### Calculate the voltage across a resistor using Thevenin's Theorem

I'm thinking I should apply Thevenin's Theorem to find the voltage, but I need to find I_D in order to be able to calculate U_S.
4. ### Some Questions About Thevenin's Theorem

(1) We want to find the voltage across ##R_L## (2) We remove the load and label the terminals ##V_T## (3) The equivalent network of (2) So basically the voltage across the load is ##V_{th}## but when we find the equivalent network we put that same voltage behind a Thevenin...
5. ### Engineering Finding the maximum power delivered using Thevenin's theorem

Using mesh analysis, my simultaneous equations seem to be wrong and I can't figure out why. Any stuff that I should take note of? Attempt:
6. ### Thevenin's Theorem -- Using transformations to find the equivalent resistance

Hello Guys, I really need help, I am trying to simplify this circuit to calculate Rth and I got stuck.
7. ### Is it the Thévenin theorem?

I just need the meaning of In.
8. ### Thevenin's Theorem, Superposition & Norton's Theorem

Homework Statement FIGURE 1 shows a 50 Ω load being fed from two voltage sources via their associated reactances. Determine the current i flowing in the load by: (a) applying Thévenin’s theorem (b) applying the superposition theorem (c) by transforming the two voltage sources and their...
9. ### How to use Thevenin to find R and I?

Homework Statement In the circuit shown, in the image, the variable resistor R is consuming maximum power. Determine: a) resistance for R b) power for R c) current for R3 and its direction Homework Equations The Attempt at a Solution I tried getting IA(the direction is shown with arrows...
10. ### AC Circuit and Thevenin's theorem

Homework Statement I'm asked to find the thevenin equivalent circuit, the load being ##R_1## ##e(t)=E_0\cos{(\omega t)}## ##R_1=1k\Omega \ R_2=R_3=1k\Omega## ##C=220nF \ f = 250Hz \ E_0=10V## Homework Equations The Attempt at a Solution ##Z_{th} = Z_{R_2}//(Z_c+Z_{R_3}) =...
11. ### Engineering Simple transformer circuit with 3 resistors

Homework Statement 2. Homework Equations [/B] V1N2=V2N1 I1N1=I2N2 The Attempt at a Solution For a part[/B] I try to draw 3 mesh but I cannot write down the equation. Can someone help me out?
12. ### Thevenin's theorem issue

Homework Statement given the circuit shown below find the the vanin equivalent at resistance R. Homework Equations the resistances on the right side of the circuit can be simplified: 18 || (24+12) = 12 kΩ. The voltage can be found from 2 mA * 12 kΩ = 24 V. The voltage Va = 12-24 = -12 V...
13. ### Need help understanding the proof of Thevenin's theorem

Hello. Uh, I'm trying to undestand how to prove Thevenin's theorem. The Sadiku book puts an independent current source where the load used to be in order to reach the equation: V = Vth + I*Rth. I do understand how he reaches that conclusion after putting the source, what I don't understand is...
14. ### How to find the equivalent Thevenin's resistance?

Homework Statement Find the Thevenin's equivalent with respect to points A and B Homework Equations 3. The Attempt at a Solution [/B] The resistance i found to be ##R_t=(R_2+R_1)||R_3+R_4## and that is the correct expression but for the voltage source the book gives...
15. ### Engineering Solving circuit with Thevenin's theorem

Hey guys, I am supposed to solve for voltage and current on R4 using Thevenin's theorem here. Values are following: U = 100V R1 = 310 R2 = 610 R3 = 220 R4 = 570 R5 = 200 Now, I know I need to solve for Rth and Vth, so I put the circuit into simulation and figured out voltage on R3 is equal to...
16. ### Thevenin's Theorem Problem

Homework Statement Determine the voltage across ##R_3## in the following figure assuming an input voltage ##v_0## of 10V is applied across the open terminals. Let ##R_1=3\Omega##, ##R_2=15\Omega##, ##R_3=10\Omega##, ##R_4=5\Omega## and ##R_5=2\Omega## and Homework Equations The Attempt at...
17. ### Is there any algebraic proof for Thevenin's theorem?

Is there any algebraic proof for Thevenin's theorem?
18. ### Applying Thévenin's theorem

Homework Statement [/B] Find the current that flows through the ##8 \Omega## Homework Equations Thévenin's theorem The Attempt at a Solution the theorem says that I can replace all the circuit to a power source and a resistor connected in series. So first I need to connect all the power...
19. ### Find the Thevenin's Equivalence of a Circuit

I don't know how to find the thevenin's equivalence of a circuit. In this question,it is required to find the thevenin's equivalence of the circuit. Firstly,I found the Rth,and the Rth is 20ohm. But I had difficulty in finding the Vth. In the first step I redrew the circuit in the following...
20. ### Solve for I and U using Thevenin's Theorem

Homework Statement Hello guys! I am getting really desperate here and I'd be very glad for any help. I have the following circuit with 5 resistors :(excuse the drawings, I am in a hurry, I hope they are sufficient) http://s11.postimg.org/8mmd2pa2b/original.png And I am supposed to solve...
21. ### Two methods -- neither works, thevenin

Homework Statement we are asked to find the tension between the R6 = 20 ohms resistor, using thevenin[/B] Homework Equations the given solution for Ethev is 27.78 The Attempt at a Solution is seen in the pictures below thank i really appreciate your help as it gets frustrating not to...
22. ### Thevenin's theorem

hello! can you tell me please which solution is correct: We need to find the Vth and Rth. Rth is easily 4Ohms, but what about Vth? 1st solution: Calculate Vth, by doing 10A=I1+I2 and 4V+2xI1=2xI2, where you find I1=6A and I2=4A, so Vth=12V 2nd solution: Calcullate Vth, by transforming the...
23. ### Finding the current Io for t>0 in a RL circuit

Homework Statement For the circuit in the attached file, find io (current) for t>0 Homework Equations The Attempt at a Solution I have included an attachment which shows the solution. However, I will copy the solution here as well for reference: When t<0, the switch is closed, the inductor...
24. ### Thevenin's and Norton's Theorem

Hi. It's me again. Right now I have some troubles with Thevenin's and Norton's theorem. Here is the circuit. I have to find the thevenin voltage Vth and thevenin resistance Rth and solve the circuit when there is a 2000Ω resistor connected to A and B. Then, I try to solve it... First, for the...
25. ### Effective resistance for Thevenin's theorem

Homework Statement Me again. I again got confused with 2 similar things done differently on two different places. Let's say we have some arbitrary circuit and we want to replace a part of it with thevenin's generator. We also need to calculate effective Thevenin's resistance, which is where i...
26. ### Thevenin's Theorem Assignment: Solving V1 & V2

Hello just wondering if any of you clever people would be able to give me some guidance on an assignment question I have been given. The notes for the course are terrible and they seem to love to through terminologies into the assignments which have not been covered in the course notes. So does...
27. ### Understanding Thevenin's Theorem

Homework Statement You have a circuit (attached pic) and want to find the Thevenin equivalent resistance and voltage. Homework Equations See below The Attempt at a Solution OK< here's what confuses me. If I simply look at the total resistance of the circuit from A and B, it seems to me that...
28. ### Thevenin's Theorem with Source Transforms

Homework Statement I was able to find the Thevenin equivalent between ##A## and ##B## using loop analysis and then Ohm's law: The Thevenin equivalent was ##V_{th} = -4.0 V## in series with ##R_{th} = 0.8 k##. Now I had a question about solving the problem using a different approach. I...
29. ### Norton's Theorem and Thevenin's theorem

Homework Statement For some reason I don't use this theorem since Thevenin's theorem is more common. I'm asked to find the Norton equivalent source between the terminals ##A## and ##B## for the following: Homework Equations The Attempt at a Solution The first step is to short ##R_2##...
30. ### Thevenin's Theorem: Solving Homework Statement on Load Current

Homework Statement FIGURE 1 shows a 50 Ω load being fed from two voltage sources via their associated reactances. Determine the current i flowing in the load by: (a) applying Thévenin’stheorem (b) applying the superposition theorem (c) by transforming the two voltage sources and their...
31. ### Thevenin's Theorem Help

Hello, As part of a module of a HNC I'm looking at Thevenin's & Norton's Theorems. As it's distance learning and I work full-time it's easier for me to ask on here rather than contact the course lecturer - they're finished by the time I get home and I'm hoping I might get a response to my query...
32. ### Solving Thevenin's Theorem: 12V, 6A Circuit

In the given circuit having a voltage source of 12V and current source of 6 A..we have to find thevenin circuit to left of terminals a &b.. Now if we'll find the thvenin resistance by shorting across 12 V battery and open circuiting across the current source.. as I solved it shud be.. 4//6//6...
33. ### Thevenin's Theorem: Solving Complex Circuits

In this part , m doubtful about finding equivalent resisitance and thevenin's resistance (Rth).. m giving a circuit in whi there we have to find current through 4 ohm resistancce connected acreoss terminals A& B.., on left side of A, B there is a battery of 8V and a resitance of 2 ohm in...
34. ### Thevenin's Theorem: AC Circuits with Different Frequencies

My textbook has this excerpt: I am not sure why it refers to Example 10.6 as that is unrelated. I don't understand to be honest. How can you calculate the Thevenin equivalent at different frequencies? Let us say that you have two voltage source: v1(t)=10cos(5t) and v2(t)=10cos(2t). So how...
35. ### Wheatstone Bridge with Thevenin's Theorem

Homework Statement http://imageshack.us/a/img685/602/homeworkprobsg29.jpg [Broken] The bridge circuit provides a good illustration of the use of Thevenin's theorem. Find the current through the bridge resistor (50Ω). Homework Equations V = IR source transformations, current division...
36. ### Thevenin's Theorem: Solving Homework Equations

Homework Statement Homework Equations Vth = Isc * Rth The Attempt at a Solution I'm not sure what those triangles mean but I assume it means they belong to the same node so I redrew as such. After that I found the Rth to be Rth = \frac{2R*R}{3R} + R = \frac{5}{3}R Edit : I found Isc =...
37. ### Using Thevenin's theorem on a High pass filter with a DC Offset

Homework Statement A 1kHz square wave with an amplitude of 2V (peak to peak) is applied at the input V-in of the circuit shown. The resistor R1 = R2 = 10 kΩ, and C = 0.02 μF. a) What is the effective time constant of this circuit? b) What is the minimum and maximum voltage reached at...
38. ### Engineering A circuit problem from Thevenin's theorem (I cant work Vth out)

Homework Statement Greetings to all, I can't work the Vth out (across terminals a and b) from the circuit in the image I've attached here. There was a hint in the question too:' ... Define the voltage at the left most node as 'v', and write 2 nodal equations with Vth as the right node...
39. ### Thevenin's Theorem : Reason behind 'nullifying' or 'suppressing' sources?

WHY aren't voltage sources open circuited and current sources short circuited? Thevenin's theorem (and even Superposition Theorem) states that we need to 'suppress' or 'nullify' the effect of all sources. We do this by short circuiting voltage sources and open circuiting current sources. WHY...
40. ### Use of Thevenin's theorem in Steady State Analysis

Homework Statement R1 = 29 ohm R2 = 23 ohm f = 60hz L = 20mH C = .1uF Is = 27A K = 12 See picture for circuit. Homework Equations KCL, KVL, is = Is cos (wt), V = IZ The Attempt at a Solution I first did a source conversion to volts then tried to love using KCL and the nodal method. When I...
41. ### Thevenin's Theorem question

Homework Statement [PLAIN]http://img21.imageshack.us/img21/2408/screenshot20101028at112.png [Broken] Hi, I'm new to these forums, so hopefully this is the right place to post this question. I need some help in the question above. I'm not obtaining the right answer for this question and...
42. ### Thevenin's Theorem and Norton's Theorem

Hi guys, I'm stuck with determining how will I solve this circuit using Thevenin's and Norton's Theorem. Given Problem: From the circuit (which is in the image), find the voltage across a 6-ohm resistor using Thevenin's Theorem and Norton's Theorem. The attempt at a solution Using KVL...
43. ### Thevenin's theorem application. HELP (this is for an exam in 2 weeks)

Homework Statement question 3 part b ( see attachment) Homework Equations thevenin theorem The Attempt at a Solution the answer should be 10.98v for Vth (thevenin equivalent voltage) all my attempts were unsuccessfull. I found voltages such as 22.2 volts i think I lake...
44. ### Thevenin's theorem question - really

Hey, I am wondering whether someone could help me with this question, attached below as an image. For some reason electronics has always been something I find difficult to comprehend and I have some deep misunderstandings, so I'm trying to work hard on the subject for my degree. My current...
45. ### Calculating IE in Amplifier Circuit with Thevenin's Theorem

Given the circuit of the amplifier shown in the uploaded figure, I'm trying to find IE (the dc emitter current). For some reason, the book I'm using, when calculating Vb which is equivalent to VTH took in consideration the resistances in the emitter which are in parallel with R2 (the given...
46. ### Determining node voltage using Mesh Analysis and Thevenin's Theorem

Homework Statement Using mesh analysis work out the currents flow through each of the three meshes. From these current values calculate the voltage of node A, and node B with respect to the ground node. Find equivalents of sub circuits A-G, B-G, A-B by applying Thevenin's theory. Then...
47. ### Thevenin's Theorem question

I have this question: A DC source has an open circuit voltage of 7.5 volts across its output terminals. the output voltage falls to 7.44 volts when a 600 ohm precision resistor is connected to the output. draw the TEC (Vt, Rt) of the source, showing all values. also show the calculations to...
48. ### Thevenin's Theorem - Dependent Source + Resistor

Hey, I'm having a bit of difficulty with this one. I spoke to my professor specifically about this problem, he worked through it, I understood him, and I worked through it later in the day. I still get it, I worked through it, and there's step at the end that we both did differently. It seems...
49. ### Understand Thevenin's Theorem Easily

ok i need a little bit of help understanding this, I've read over it ten times and it still is making no sense to me "a given network, with constant voltages and resistance produces a current flow in the load resistor equal to that which flows if the load resistor were applied across an...
50. ### Solving Circuit Problems with Thevenin's Theorem

I'm working on some circuit Problems involving Thevenin's Theorem. When there is only one power source it seems pretty straight forward, but I'm a little confused when another power sources is added. Does it matter if a second power source is facing the opposite direction of the first? I...