thevenin equivalent example problem

[PG1995]

Thanks a lot, Kerim.

You are right... it's a typo and this means that you have a great talent to analyse... circuits and texts as well. Now I will re-read the posts with the hope I can get exactly what you are looking for as answers

Seriously, I'm simply laughing. In actuality I'm quite silly with this stuff. It's just that you haven't seen my stupidity in all its glory yet.

This means that the currents of the outside meshes have a zero value. This is how I see it :wink:

I'm so sorry, Kerim. I don't get it. Do you have circuit drawing software? Please use it to make things clear.

Two nodes means there is a potential difference. A branch between the two nodes may be seen as a current path. But for 'DC circuits', if there is one path only its current has to be zero. Therefore, to have a current there must be one more path (branch) in the least between the two nodes.

Once again, sorry. Can you feel my stupidity?! If you have circuit drawing software, then please use it. Thanks.

Yes two nodes at least, and one of them could be a reference node. The circuit of your question (1 is a good example of this.

You are right... as usual :wink: And it will be up to you which equations you like to work with. And you will get always the same result. The difference is that the road you choose will be longer or shorter than the other one(s). For instance, now you are learning many ways to solve even the same circuit, later no one will stop you in using any of them... hmmmm... or none of them as well... by using a simulator :grin:

Kerim

 

[KerimF]

3: It applies to a single loop --> Only 1 unknown - In mesh analysis we need to subtract the current of loop from the current of the other. So, if we have a single loop, then we have only one current. What am I missing here?

Yes, as you said we have just one current in this case.
But since I used to complicate things in my life, I thought you were asking... to where have the other currents gone
So I drew this figures to explain my first silly answer
"RedundantLoops_01.pdf"

4: between these two nodes there must be more than 1 branch - What does "between" mean in this context?

It seems I cannot see clearly what you are asking for. The best I am able to do is to draw you some configurations having two nodes.
"TwoNodes_01.pdf"

 

[PG1995]

Thank you, Kerim.

1: But I don't see any nodes in the "TwoNodes_01" drawing.:roll: Help me, please.

2: This is confusing me since I started this thread. I would try to ask it now and try my best to convey my confusion. Please have a look on the following link: https://img708.imageshack.us/img708/3581/img0002ri.jpg

The scan also has my comments there which are an attempt to explain what is troubling me.

I have taken the Circuit #2 from the my post #1; specifically the Circuit #2 could be found here: https://img843.imageshack.us/img843/4292/norton1.jpg (Original link)

As you see the author in the "Original link" says that the circuit on left of the terminals a-b is supplying power but I don't get it. From the viewpoint of current source Io the terminal "a" should be +ve because current source is pointing toward it; that means its +ve terminal is connected with "a". But from the viewpoint of the circuit on the left of terminal a-b the terminal "a" is at -4V potential which I don't get. Do you see my confusion?

Thank you very much for all the help.

 

[KerimF]

1: But I don't see any nodes in the "TwoNodes_01" drawing. Help me, please.

Oh... so what do you call (a) and (b) in all figures?

2: This is confusing me since I started this thread. I would try to ask it now and try my best to convey my confusion. Please have a look on the following link: https://img708.imageshack.us/img708/3581/img0002ri.jpg

Who told you that a current SHOULD always go in one direction according to the node potentials; that is from a high/low potential to a low/high one?! :wink:

First we need to distinguish between the direction of a current inside an electrical element and outside of it.
Let us analyse a voltage source connected to a resistor. The current inside the voltage source is from a low potential to a high potential (this means it is a generator). The current outside of it is from high to low instead, passing in the resistor (so the resistor is a load, consuming power).

Also we need to distinguish between an assumed direction of a current and its final real direction which is based on the sign of the assumed one (as a given data or a result).

Finally if we assume that a current is said to be positive when it goes from terminal of a high potential to the terminal of the lower one, we may add:
A device is said to be a generator if the product of its voltage and current is negative, otherwise it is a receptor (as a resistor).

Do you see my confusion?

It is about signs... when writing equations we need to forget what the real values of the voltages and currents are. Instead we have to focus on the assumed directions (as positive) and the formulas we need to apply to get an equation (or equations). After getting the results (and their signs) only, we may like to discuss what is real happening in the circuit based on the results.

I think the best remedy for your confusion (I usually apply it on myself)... is to forget completely all about it and keep learning other things then rethink of it again after a while from the start... you will amaze yourself when everything will be clear to you even without getting help from anyone.

 

[PG1995]

Oh... so what do you call (a) and (b) in all figures?

From what my book says: A node is a junction of two or more branches coming together. The "a" and "b" are simple junction points, not nodes according to the book.


I need help with the query below.

2: This is confusing me since I started this thread. I would try to ask it now and try my best to convey my confusion. Please have a look on the following link: https://img708.imageshack.us/img708/3581/img0002ri.jpg

The scan also has my comments there which are an attempt to explain what is troubling me.

I have taken the Circuit #2 from the my post #1; specifically the Circuit #2 could be found here: https://img843.imageshack.us/img843/4292/norton1.jpg (Original link)

As you see the author in the "Original link" says that the circuit on left of the terminals a-b is supplying power but I don't get it. From the viewpoint of current source Io the terminal "a" should be +ve because current source is pointing toward it; that means its +ve terminal is connected with "a". But from the viewpoint of the circuit on the left of terminal a-b the terminal "a" is at -4V potential which I don't get. Do you see my confusion?

Thank you very much for all the help.

 

[KerimF]

So it is ok for your book that (a) and (b) are nodes on the figures B1 , B2 and B3... While on fig. A1, A2 and A3 these nodes could be called terminals. The good news is that the nodal theorem can be applied on a terminal (Sum of Is = 0) that is why I1=0 and I2=0 (I3=0 and it is supposed that I3=I !!! The reason of this contracdiction is that having a current source alone cannot be real, in the first place)

 

[PG1995]

2: This is confusing me since I started this thread. I would try to ask it now and try my best to convey my confusion. Please have a look on the following link: https://img708.imageshack.us/img708/3581/img0002ri.jpg

The scan also has my comments there which are an attempt to explain what is troubling me.

I have taken the Circuit #2 from the my post #1; specifically the Circuit #2 could be found here: https://img843.imageshack.us/img843/4292/norton1.jpg (Original link)

As you see the author in the "Original link" says that the circuit on left of the terminals a-b is supplying power but I don't get it. From the viewpoint of current source Io the terminal "a" should be +ve because current source is pointing toward it; that means its +ve terminal is connected with "a". But from the viewpoint of the circuit on the left of terminal a-b the terminal "a" is at -4V potential which I don't get. Do you see my confusion?

It's dependent current source which is responsible for negative potential at "a".

1:
Please have a see on this link: **broken link removed**

The linked diagram is redrawing of the Figure 4.35(b) found in the Original Link in my first post above:

The Circuit #2 could be found here in full context here: https://img843.imageshack.us/img843/4292/norton1.jpg (Original link)

Let's hope I have it right this time. Please let me know.

 

[KerimF]

I am afraid that you are supposing values more than a circuit can hold. The whole cicuit has only 2 nodes 'a' and 'b'. I personally cannot convince myself that the potential between 'a' and 'b' (like Vab) could be given 2 values then I add or substract them. During the solution of this circuit (or any circuit) the voltage between two nodes (or terminals) is known or not. If it is known it helps us calculate some other unknowns. If it is unknown, there must be a way to find it (by solving one or more equations for example).

Added:
It seems to me, you have a very clever mind to the point you cannot accept that such simple circuits need books to be explained :grin: All your works are right when you solve the problems as simple ones... But sometimes your mind refuses to imagine that they are indeed simple for you... and looks for some more complex analysis (in a way or another) to satisfy its power :wink: I have to confess that I use to fall in this trap myself

 

[jony130]

Look at your circuit when we connect 1V voltage source instead of current source.

The voltage is positive so current in 2Ω resistor flow in the opposite direction then Ix.
And this means that current in dependent current source will flow in opposite direction to.
But despite this circuit still is supplying power to the load (1V voltage source).
And this means that we charging the voltage source (battery).

 

[PG1995]

Thank you, Kerim, Jony.

@ Jony: It seems you have a copy of the book I'm using!:grin: Have you also used the same book? Just curious.

 

[jony130]

Jony: It seems you have a copy of the book I'm using!:grin: Have you also used the same book? Just curious.

No, I just download the book for curiosity.