How to find the equivalent Thevenin's resistance?

In summary, the conversation discusses finding the Thevenin's equivalent with respect to points A and B. The resistance is found to be Rt=(R2+R1)||R3+R4, but the book gives a different expression for the voltage source. The conversation then questions the inclusion of R4 in the voltage source expression, to which it is explained that the Thevenin voltage is given by the open-circuit voltage at the output. When AB is an open circuit, the current is zero and the Thevenin voltage is obtained. The Thevenin resistance does include R4, so its effects are included when a load is connected and current flows.
  • #1
doktorwho
181
6

Homework Statement


Capture.JPG

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
##\frac{R_3}{R_1+R_2+R_3}*(V_1+V_2)-V_4##
I understand that the first part is a voltage divider but the second i don't get? Dont we have a voltage drop along ##R_4## as well? How could we ignore it and just subtract ##V_4##? Could you explain?
 
Physics news on Phys.org
  • #2
doktorwho said:
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
##\frac{R_3}{R_1+R_2+R_3}*(V_1+V_2)-V_4##
I understand that the first part is a voltage divider but the second i don't get? Dont we have a voltage drop along ##R_4## as well? How could we ignore it and just subtract ##V_4##? Could you explain?
The Thevenin voltage is given by the open-circuit voltage at the output. If that is the case, what must be the current through ##R_4## in that circumstance?
 
  • #3
gneill said:
The Thevenin voltage is given by the open-circuit voltage at the output. If that is the case, what must be the current through ##R_4## in that circumstance?
The same current that flows into A is the current through B but still can't see why its not included... That would be the case if the current is 0 but it can't be zero right?
 
  • #4
doktorwho said:
The same current that flows into A is the current through B but still can't see why its not included... That would be the case if the current is 0 but it can't be zero right?
When AB is an open circuit, the current is zero. The Thevenin voltage is obtained when the output is an open circuit.

Note that the Thevenin resistance does include R4. So its effects are included when a load is connected and current flows.
 
  • Like
Likes doktorwho

Related to How to find the equivalent Thevenin's resistance?

1. What is Thevenin's Theorem and why is it important?

Thevenin's Theorem is a fundamental principle in circuit analysis that states any linear circuit can be represented by an equivalent circuit with a single voltage source and a single resistor. It is important because it simplifies complex circuits, making them easier to analyze and design.

2. How do I find the equivalent Thevenin's resistance?

To find the equivalent Thevenin's resistance, you need to remove all voltage sources and short-circuit all current sources in the original circuit. Then, measure the resistance across the two terminals where the voltage source was originally connected. This resistance value is the equivalent Thevenin's resistance.

3. Can I use Thevenin's Theorem for non-linear circuits?

No, Thevenin's Theorem only applies to linear circuits. Non-linear circuits require more complex analysis techniques.

4. Is Thevenin's resistance the same as the total resistance of the circuit?

No, Thevenin's resistance is the resistance seen by the load at the output terminals of the circuit. It is not necessarily the same as the total resistance of the circuit.

5. Why is Thevenin's resistance useful in circuit analysis?

Thevenin's resistance allows us to simplify complex circuits into a single equivalent circuit, making analysis and design easier. It also helps us determine the maximum power that can be transferred from a linear circuit to a load.

Similar threads

Complex RLC Circuit Problem (System of diff eqs)
    • Engineering and Comp Sci Homework Help
Replies
6
Views
868
Calculating the Thevenin's Resistance of a Breadboarded Circuit
    • Engineering and Comp Sci Homework Help
Replies
9
Views
2K
Engineering Solving Circuit Equations: A Struggle
    • Engineering and Comp Sci Homework Help
Replies
15
Views
2K
Engineering Finding the Thevenin Equivalent Circuit for a Network with a Load Resistor
    • Engineering and Comp Sci Homework Help
Replies
1
Views
1K
Engineering How to Calculate Thevenin Equivalent Circuit
    • Engineering and Comp Sci Homework Help
Replies
5
Views
1K
Determine Thevenin equivalent circuit.
    • Introductory Physics Homework Help
Replies
1
Views
259
Engineering Find the Thevenin equivalent circuit
    • Engineering and Comp Sci Homework Help
2
Replies
42
Views
5K
Are Overly Complicated Homework Problems Beneficial for Student Learning?
    • Engineering and Comp Sci Homework Help
Replies
2
Views
941
Engineering How do I find Vth with the node voltage method?
    • Engineering and Comp Sci Homework Help
Replies
10
Views
2K
Why is the Thevenin resistance in this problem 3.2 kΩ?
    • Engineering and Comp Sci Homework Help
Replies
17
Views
2K

Hot Threads

Recent Insights

Back
Top