# Thevenin equivalent circuit

• Alexander Max
In summary, the problem at hand is finding the Thevenin equivalent circuit without the load resistor. The process involves removing the load resistor, finding the open circuit voltage across terminals a and b, and suppressing all independent sources (voltage sources are replaced with short circuits and current sources are removed entirely). The equivalent circuit resistance across the break can then be determined and used to form the final equivalent circuit.
Alexander Max

## Homework Statement

I am to find the thevenin equivalent circuit without the load resistor (to the left of terminals a &b

## Homework Equations

From class notes:
2- find the open circuit voltage across a & b
3- Remove all voltage sources (replace with short circuit)
4- Detrmine the equivalent circuit resistance across the break
5- Form an equivalent circuit

## The Attempt at a Solution

I have not come across the symbol that looks like an 8 with the 2amps next to it so far, and i don't understand how this will effect my circuit, is it a voltage source, how will it effect the resistors?
Without acknowledging it,
my resistors are all in parralel so Restance total is
1/RT = 1/R1 + 1/R2 + 1/R3
1/RT = 1/4 + 1/12 + 1/1
1/RT = 3/12 + 1/12 + 12/12
1/RT = 16/12
RT = 12/16
RT = 0.75

32v/0.75 ohms = 42.667 Amps
Vab = 32 - 1x42.667Amps = -10.667 Volts

Resistance looking in has already been calulated as 0.75 ohms

#### Attachments

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Hello Alex, and welcome to PF :)

The 2A thingy is a (slightly outdated) symbol for a current source.

I don't see how you can consider all R as parallel.

Hi Alexander Max, Welcome to Physics Forums.

As BvU stated, the two-circle symbol represents a current source. It's a bit outmoded as a schematic symbol, but it still crops up fairly often.

Allow me to amend your algorithm's item 3 a bit, since in its given form it doesn't address current sources:

3 - Suppress all independent sources: Replace voltage sources with a short circuit and all current sources with an open circuit (simply remove them entirely).

Hello,

Thevenin's theorem is a useful tool for simplifying complex circuits and determining the equivalent circuit for a specific load. To find the Thevenin equivalent circuit without the load resistor, you will follow the steps outlined in your class notes.

First, remove the load resistor and find the open circuit voltage across terminals a and b. Next, remove all voltage sources and replace them with short circuits. This will effectively remove the 8 with 2 amps symbol, as it is a voltage source. The resistors will not be affected by this, as they are only affected by the voltage and current in the circuit.

Next, determine the equivalent circuit resistance across the break. In this case, the resistors are in parallel, so the total resistance will be 0.75 ohms.

Finally, you can form the equivalent circuit by combining the open circuit voltage and the equivalent resistance. The result will be a voltage source of -10.667 volts in series with a resistor of 0.75 ohms.

I hope this helps clarify the steps for finding the Thevenin equivalent circuit without the load resistor. Let me know if you have any further questions. Good luck with your homework!

## 1. What is a Thevenin equivalent circuit?

A Thevenin equivalent circuit is a simplified representation of a complex circuit that contains a voltage source and a single equivalent resistor. It is used to analyze the behavior of a circuit and determine the voltage and current at a specific point.

## 2. How is a Thevenin equivalent circuit calculated?

To calculate the Thevenin equivalent circuit, the circuit is first simplified by removing all loads and replacing them with a wire. Then, the voltage across the open terminals is measured to determine the Thevenin voltage (Vth). Next, the circuit is restored and the equivalent resistance (Rth) is calculated by finding the total resistance between the open terminals.

## 3. What is the purpose of using a Thevenin equivalent circuit?

The purpose of using a Thevenin equivalent circuit is to simplify a complex circuit into a single voltage source and resistor, making it easier to analyze and understand the behavior of the circuit. It also allows for easier calculations and predictions of voltage and current at a specific point in the circuit.

## 4. Can a Thevenin equivalent circuit be used for any type of circuit?

Yes, a Thevenin equivalent circuit can be used for any type of circuit, as long as it contains resistors and can be simplified into a single voltage source and resistor. It is commonly used in DC circuits, but can also be applied to AC circuits.

## 5. How accurate is a Thevenin equivalent circuit compared to the actual circuit?

A Thevenin equivalent circuit is an approximation of the actual circuit, so it will not be 100% accurate. However, it can provide a good estimation of the behavior of the circuit and is a useful tool for circuit analysis and design.

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