Thevenin equivalent circuit parameters

[Narks]

Homework Statement

https://www.physicsforums.com/attachment.php?attachmentid=32837&stc=1&d=1299373667

Determine the Thevenin equivalent circuit parameters, VTh and RTh, referred to terminals A and B of the circuit shown below?

Homework Equations

The Attempt at a Solution

My only question is this step:
https://www.physicsforums.com/attachment.php?attachmentid=32838&stc=1&d=1299373667
Converted current source to voltage source (V = IR = 10 x 2 = 20 V), then combined the 10 ohm and 5 ohm resistor.

I'm pretty sure I've just ignored the polarity of the current source to get here - I've always been confused as to what to do with converting sources and polarity. Is this correct? If not, what is the proper way to convert the current source to a voltage source (assuming that is the correct method to solve the problem)?

Thanks!

 

[lorenb]

ya, that looks right. Just think that the 2 amps is making a loop through the 10 ohm resistor. If you made a circle on the left loop with an arrow pointing in the same direction as the current source. The current would go up through the 10 ohm resistor. So put your voltage source so the + side is pointing up.

 

[gneill]

1. The polarity of the voltage source in the second figure should be reversed.
2. You're not done yet. You've still got to resolve the 15Ω/5Ω voltage divider into a single resistance and voltage source.

 

[winblowzxp]

Change your current source into a voltage source, which should give you a 20V voltage source. When you redraw the circuit, put the resistor in series with the voltage supply and that will give you the voltage divider that gneill was referring to.

 

[DeeNos]

I would like to clarify that the Thevenin equivalent circuit parameters refer to the simplified circuit that can be used to model the behavior of a more complex circuit. The Thevenin equivalent circuit is essentially a voltage source in series with a resistor, and it is used to analyze the behavior of a circuit when connected to an external load.

In order to determine the Thevenin equivalent circuit parameters, VTh and RTh, we can use the following steps:

1. Find the open circuit voltage (Voc) across terminals A and B. This can be done by removing the load resistor and finding the voltage across those terminals.

2. Find the equivalent resistance (Req) seen from terminals A and B. This can be done by shorting all the voltage sources and opening all the current sources, and then calculating the equivalent resistance.

3. Once we have the open circuit voltage and the equivalent resistance, we can determine the Thevenin equivalent voltage (VTh) by simply setting the voltage source value to Voc and the resistance value to Req.

4. To find the Thevenin equivalent resistance (RTh), we can use the following equation: RTh = Req.

In regards to the specific problem provided, the step of converting the current source to a voltage source is correct. The polarity of the voltage source will depend on the direction of the current through the current source. If the current is flowing from terminal A to terminal B, the voltage source will have a positive polarity, and if the current is flowing in the opposite direction, the polarity will be negative. In this case, it looks like the current is flowing from terminal B to terminal A, so the polarity of the voltage source would be negative.

I hope this helps clarify the steps for determining the Thevenin equivalent circuit parameters. If you have any further questions or concerns, please don't hesitate to ask. I am always happy to help others understand and learn more about scientific concepts.