this is my lat final exam question and till niw i couldnt solve it i try nodal , mesh anaylsis but nothing worked

 

hi Chadheya,
Welcome to AAC,
Please post your attempt so that we can advise where you are going wrong.
E

 

Hello,

Also, there seems to be no question here. It looks like the question is, "What it hs current of that constant current source A", but there's no other criterion to work with that question. So at least post the question
Also, filenames in (what looks like) Farsi may not work very well on some people's computers. Note the thumbnail looks different than the actual picture too.

 

Start with what you know -

1) Ix x 40 = Vab
2) Use result in 1) to compute I in 80 ohms
3) Use results in 1) and 2), the currents, so sum current at node of 160Ix and the I80 and I40 (=160Ix)

Keep proceeding that way.

Regards, Dana.

 

this is my lat final exam question and till niw i couldnt solve it i try nodal , mesh anaylsis but nothing worked

What is it that you are trying to solve?

If you are trying to find the value of that current source, then what are you trying to solve it in terms of? Ix? Or Vab?

You should be able to see that there isn't a single, constant valid answer for that current source. I can set that current to anything I want and the values of the voltages and currents elsewhere in the circuit adjust in response.

Please post the actual question. Also, post YOUR best attempt, no matter how incomplete or how incorrect, to work the problem. That is what provides us with a starting point to try to help you.

 

Hi,

That was my question too. Solve for Va-Vb maybe? It's guesswork at this point and i think it is because part of the picture is missing.

 

Solve for ?A I think.....

Regards, Dana.

 

Hi,

That was my question too. Solve for Va-Vb maybe? It's guesswork at this point and i think it is because part of the picture is missing.

View attachment 150357

Most likely, the problem asks them to find the value that the question mark needs to be when Vab is equal to a specific value. The diagram is probably used for different problems so that the problem text can create a seemingly different problem without having to have a new figure.

 

Solve for ?A I think.....

Regards, Dana.

In terms of what? Ix? Vab? Ptotal?

 

Solve for ?A I think.....

Regards, Dana.

Hi,

Please see the post right after yours. Thanks.

 

Its to solve for the current A....

Regards, Dana.

 

Its to solve for the current A....

Regards, Dana.

Then please do so.

So as not to give the answer, just tell us if it is less than 2 A or greater than (or equal) to 2 A.

 

Not either, answer is in terms of Ix.

Regards, Dana.

 

Not either, answer is in terms of Ix.

Regards, Dana.

Why is it in terms of Ix? Why not Vab? Why not some other voltage across or current through some component?

Ix is the control signal for the current-controlled voltage source. There's nothing in the problem statement (or lack thereof) that says that the problem is looking for the setting of the current source as a function of Ix. If nothing else is given (which I doubt was the case), then it is not unreasonable to express I0 (what I will call the current source output) as a function of Ix. It's arguably more reasonable to express it as a function of Vab. But probably the most reasonable and defensible thing to do is express Vab as a function of I0.

Since the TS hasn't been back to either provide more information or show their best attempt, it's entirely possible that they only wanted someone to work their homework for them and since that didn't happen they don't care to try to actually learn something. If that's not the case, then hopefully they will come back. It's only been a day.

 

I simply took Ix as a "known" amount, I know that seems odd but
that's how I interpreted the problem given that the unknown was
?A as typed, Ix was not typed as ?Ix.

Maybe that's over reach, but its what I did. Maybe that's why I am not allowed
to design systems that affect public safety......

Regards, Dana.

 

I simply took Ix as a "known" amount, I know that seems odd but
that's how I interpreted the problem given that the unknown was
?A as typed, Ix was not typed as ?Ix.

Maybe that's over reach, but its what I did. Maybe that's why I am not allowed
to design systems that affect public safety......

Regards, Dana.

Ix is just whatever current happens to be flowing downward in the 40 Ω resistor. Whatever that current happens to be, that is the signal that is controlling the voltage output of the current-controlled voltage source at the top. That's all Ix is.

 

I simply took Ix as a "known" amount, I know that seems odd but
that's how I interpreted the problem given that the unknown was
?A as typed, Ix was not typed as ?Ix.

Maybe that's over reach, but its what I did. Maybe that's why I am not allowed
to design systems that affect public safety......

Regards, Dana.

Hi,

If you want to solve in terms of ix that is fine, but be aware that the criterion has not actually been given yet that's why we are wondering about this.

For two better examples of what we are wondering about, see the attachment.
Note the top diagram shows nothing to solve for, and believe it or not that has the same basic problem that the original circuit had: no solution criterion.
The bottom diagram really brings this point home though, because it's a very simple circuit yet we dont know what the asker wanted us to solve A for. The only guess i think is that it has something to do with the voltage between 'a' and 'b', but that's just a guess.
Note A can be 1, 10, 100, 1000, or any number, because we have no criterion to guide us.

In words:
"How much force does it take to push a bowling ball?"
We need more information to figure this out