# Thevenin equivalent resistance problem

• glover261
In summary: Take the original circuit, and find the current which flows through a wire which is connected to the two terminals. (This is the short circuit current.)This is the same current which will flow through the Thevenin equivalent circuit if its terminals are shorted.In other words, this current times the Thenenin resistance is equal to the Thevenin voltage.Sorry I don't understand, the short circuit current is the current flowing through the wire when the voltage source is removed?Take the original circuit, and find the current which flows through a wire which is connected to the two terminals. (This is the short circuit current.)This is the same current which will flow through the Thevenin equivalent circuit if its terminals are shorted.
glover261

V=IR

## The Attempt at a Solution

[/B]
I found that the current around the circuit was 5mA using kirchhoffs law ( i think)
If this is true then the T.E.V should be the voltage across the 120ohm resistor which is .6V (120*5e-3). Now I'm stuck and not sure how to find the T.E.R, thankyou

glover261 said:

## Homework Statement

[ IMG]http://i.imgur.com/XUot0kO.png[/PLAIN]

V=IR

## The Attempt at a Solution

I found that the current around the circuit was 5mA using kirchhoffs law ( i think)
If this is true then the T.E.V should be the voltage across the 120ohm resistor which is .6V (120*5e-3). Now I'm stuck and not sure how to find the T.E.R, thankyou[/B]
Hello glover261. Welcome to PF !

So far, so good.

What have you been taught regarding how to find the Thevenin equivalent resistance ?

SammyS said:
Hello glover261. Welcome to PF !

So far, so good.

What have you been taught regarding how to find the Thevenin equivalent resistance ?
Hi thanks, I thought you were supposed to take out all components except resistors in the circuit, current sources by open circuit and voltage sources through short circuit. Then just add up the total resistance of all the resistors, but that method does not seem to work on this problem, as none of the answers are the total resistance.

glover261 said:
Hi thanks, I thought you were supposed to take out all components except resistors in the circuit, current sources by open circuit and voltage sources through short circuit. Then just add up the total resistance of all the resistors, but that method does not seem to work on this problem, as none of the answers are the total resistance.
That's not quite right. You don't simply add all the resistances. You find the equivalent resistance across the terminals.

glover261 said:
Hi thanks, I thought you were supposed to take out all components except resistors in the circuit, current sources by open circuit and voltage sources through short circuit. Then just add up the total resistance of all the resistors, but that method does not seem to work on this problem, as none of the answers are the total resistance.
Is "adding up the total resistance of all the resistors" really what happens in a circuit? Do parallel resistors add?

EDIT: I see sammy beat me to it.

Aren't they all in series though? or am i missing something

glover261 said:
Aren't they all in series though? or am i missing something
You must be missing something.

Draw what you have when the voltage source is shorted.

glover261 said:
Aren't they all in series though? or am i missing something
Probably be a good idea to go back to basics and study what parallel and series really look like. This is a very common difficulty in beginning study of circuits so it's best to get really solid with it in the beginning.

EDIT: dammit, sammy, you're too fast for me

SammyS said:
You must be missing something.

Draw what you have when the voltage source is shorted.

View attachment 99280

Sorry I still can't see it

glover261 said:
Sorry I still can't see it
Probably be a good idea to go back to basics and study what parallel and series really look like. This is a very common difficulty in beginning study of circuits so it's best to get really solid with it in the beginning.

glover261 said:
Sorry I still can't see it
See the terminals?

(phinds beat me this time !)

SammyS said:
See the terminals?

(phinds beat me this time !)

So, the 180 and 100 resistors are in parallel. So Rt = 1/((1/180)+(1/100)) + 120 = 184 ohms? Is that right because I thought for a pair of components to be in parallel, both sides had to be connected to the same node.

glover261 said:
So, the 180 and 100 resistors are in parallel. No.

So Rt = 1/((1/180)+(1/100)) + 120 = 184 ohms?

Is that right because

I thought for a pair of components to be in parallel, both sides had to be connected to the same node. This is correct.
See the terminals?

SammyS said:
See the terminals?

What do they mean?

glover261 said:
What do they mean?
Find the equivalent resistance across the terminals.

Look at the nodes again.

There is an alternate way to find the Thevenin resistance.

Take the original circuit, and find the current which flows through a wire which is connected to the two terminals. (This is the short circuit current.)

This is the same current which will flow through the Thevenin equivalent circuit if its terminals are shorted.

In other words, this current times the Thenenin resistance is equal to the Thevenin voltage.

## What is Thevenin equivalent resistance problem?

The Thevenin equivalent resistance problem is a method used to simplify complex electrical networks into a single circuit with a single voltage source and a single resistance. It is commonly used to analyze and solve circuits with multiple resistors and voltage sources.

## How do you find the Thevenin equivalent resistance?

To find the Thevenin equivalent resistance, you must first remove the load resistor from the circuit and calculate the resistance between the two terminals where the load was connected. This value is the Thevenin resistance.

## What is the purpose of finding the Thevenin equivalent resistance?

The purpose of finding the Thevenin equivalent resistance is to simplify a complex circuit into a single equivalent circuit, making it easier to analyze and solve for the desired parameters. It also allows for easier replacement of components and predicting the behavior of the circuit.

## What are the limitations of the Thevenin equivalent resistance method?

The Thevenin equivalent resistance method assumes that the circuit is linear and that the load resistor is resistive. It also does not take into account components such as capacitors and inductors, which may affect the behavior of the circuit. Additionally, it may not accurately represent the behavior of the circuit at high frequencies.

## How is the Thevenin equivalent resistance used in practical applications?

The Thevenin equivalent resistance is commonly used in various fields of engineering, such as electronics and telecommunications, to analyze and design circuits. It is also used in troubleshooting and predicting the behavior of complex circuits. In some cases, it can also be used to simplify and reduce the complexity of a circuit for practical purposes.

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