# Solve a circuit using node voltage method

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#### João Sampaio

Joined Jan 30, 2018
13
Hi!

Can someone help me solving the circuit using node voltage method?

thank you

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#### MrAl

Joined Jun 17, 2014
8,479
Hi,

Start by choosing a ground (0v) node and numbering the others 1 through N.

#### WBahn

Joined Mar 31, 2012
26,398
You need to show YOUR best work to solve YOUR homework. That way we can see what you did right and where you might be going astray so that we can help nudge you back onto a good path.

#### João Sampaio

Joined Jan 30, 2018
13
Hi,

Start by choosing a ground (0v) node and numbering the others 1 through N.
have already done that, but the results don't match with the results that i got in multisim so i want to see someone solving the circuit in order to understand what i did wrong.

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#### João Sampaio

Joined Jan 30, 2018
13
You need to show YOUR best work to solve YOUR homework. That way we can see what you did right and where you might be going astray so that we can help nudge you back onto a good path.

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#### WBahn

Joined Mar 31, 2012
26,398
Here's a hint to help you check your work (assuming I didn't make any mistakes). That dependent source is the only source that is putting power into the circuit and it's doing so at a rate of nearly 44 kW.

#### WBahn

Joined Mar 31, 2012
26,398
have already done that, but the results don't match with the results that i got in multisim so i want to see someone solving the circuit in order to understand what i did wrong.
Since my crystal ball is in the shop, I can't see what results you got in multisim, so I have no idea whether they are right or not. Nor do I have any clue as to where and how they agree and disagree with what you got.

The only result I see in your work here is that V3 = -130.5 V.

What about the rest of the voltages and currents?

Are those results self-consistent, or are they contradictory?

#### João Sampaio

Joined Jan 30, 2018
13
Since my crystal ball is in the shop, I can't see what results you got in multisim, so I have no idea whether they are right or not. Nor do I have any clue as to where and how they agree and disagree with what you got.

The only result I see in your work here is that V3 = -130.5 V.

What about the rest of the voltages and currents?

Are those results self-consistent, or are they contradictory?
The only thing i need to know is the u3, node 3 voltage and u2, node 2 voltage.

i considered that current I1 is the 20A current and that current its equal to I2(the current that floats from node 3 to node 2) plus i (the current that floats from the node 3 to the reference node.

#### WBahn

Joined Mar 31, 2012
26,398
u3 may be the only thing you need to report. But wouldn't it be nice to be able to check if your answer is correct?

Solve for the rest of the voltage and currents assuming that your answer for u3 is correct and see if they are all self consistent.

#### WBahn

Joined Mar 31, 2012
26,398
Similarly, look at the simulator results for all of the node voltages and branch currents and see if those are consistent with the problem. If they are, then you can have confidence in them. If not, then there is something wrong with your simulation (usually meaning that the circuit you simulated doesn't match the circuit in the problem).

#### João Sampaio

Joined Jan 30, 2018
13
Similarly, look at the simulator results for all of the node voltages and branch currents and see if those are consistent with the problem. If they are, then you can have confidence in them. If not, then there is something wrong with your simulation (usually meaning that the circuit you simulated doesn't match the circuit in the problem).
I have already done that, and thats why i'm asking for help.
I solved the circuit in many different ways.

#### WBahn

Joined Mar 31, 2012
26,398
I have already done that, and thats why i'm asking for help.
I solved the circuit in many different ways.
If you've solved the circuit many different ways, then it should be a trivial matter to post what you got for the node voltages and branch currents, shouldn't it?

If you've simulated the circuit in Multisim, then it should be a trivial matter to post what it got for the node voltages and branch currents, shouldn't it?

#### João Sampaio

Joined Jan 30, 2018
13
If you've solved the circuit many different ways, then it should be a trivial matter to post what you got for the node voltages and branch currents, shouldn't it?

If you've simulated the circuit in Multisim, then it should be a trivial matter to post what it got for the node voltages and branch currents, shouldn't it?
.... i dont need more questions... i just need a solution... i tried everything i know based on what i learned

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#### MrAl

Joined Jun 17, 2014
8,479
I have already done that, and thats why i'm asking for help.
I solved the circuit in many different ways.
Hi,

Quick note here...

The current 'i' is not equal to 3*U3, it is equal to U3/3. Try using that info. That's Ohm's Law.

#### João Sampaio

Joined Jan 30, 2018
13
Hi,

Quick note here...

The current 'i' is not equal to 3*U3, it is equal to U3/3. Try using that info. That's Ohm's Law.
i dind't do that, if you look better, you can see that i wrote i=U3/3...

#### WBahn

Joined Mar 31, 2012
26,398
.... i dont need more questions... i just need a solution... i tried everything i know based on what i learned
So what you learned doesn't allow you to find the voltages at all the nodes and the currents in all the branches?

In other words, you aren't interested in learning how to check your work, you just want someone to do your work for you.

Thank you for at least finally posting your schematic so that at least we can stop trying to do mind reading on that point.

In the original circuit, the current that is controlling the dependent source is the current going THROUGH the 3 Ω resistor, right?

In your Multisim simulation, is the current that is controlling the dependent source going THROUGH the 3 Ω resistor?

#### MrAl

Joined Jun 17, 2014
8,479
i dind't do that, if you look better, you can see that i wrote i=U3/3...
Hi,

Oh yes you are certainly correct. I didnt see that part up there. I'll make a somewhat more clear drawing.
I'll also take another look too.

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#### João Sampaio

Joined Jan 30, 2018
13
So what you learned doesn't allow you to find the voltages at all the nodes and the currents in all the branches?

In other words, you aren't interested in learning how to check your work, you just want someone to do your work for you.

Thank you for at least finally posting your schematic so that at least we can stop trying to do mind reading on that point.

In the original circuit, the current that is controlling the dependent source is the current going THROUGH the 3 Ω resistor, right?

In your Multisim simulation, is the current that is controlling the dependent source going THROUGH the 3 Ω resistor?
i checked all the voltages and currents and i've solved other problems with this method.
you can see in the photo that I wrote a lot in that paper and obviously it's not "not want to work".
if i could help someone solving a circuit like this i would not mind to, at least, writing the main equations to the exercise.
You can see my main equations, and based on the circuit you can see if you agree with them or not. It's all that i needed.
And this is not a work, it is an exercise that I want solve alone, but I can pass this one and ask my teacher then.
I just wanted to answer it because it is driving me crazy not making it right.
So if you're not able to help ... or say something about my equations because you dont know my way to use this method, dont say anything at all.
Someone who understands this kind of stuff can solve it easly and I'm sure I saw it in this forum. People have done that.

And yes obviously the current is controlling the dependent source and you didnt need multisim's schematic to know, is in the previous image.

#### João Sampaio

Joined Jan 30, 2018
13
Hi,

Oh yes you are certainly correct. I didnt see that part up there. I'll make a somewhat more clear drawing.
I'll also take another look too.
thank you!

#### WBahn

Joined Mar 31, 2012
26,398
i checked all the voltages and currents and i've solved other problems with this method.
you can see in the photo that I wrote a lot in that paper and obviously it's not "not want to work".
if i could help someone solving a circuit like this i would not mind to, at least, writing the main equations to the exercise.
You can see my main equations, and based on the circuit you can see if you agree with them or not. It's all that i needed.
And this is not a work, it is an exercise that I want solve alone, but I can pass this one and ask my teacher then.
I just wanted to answer it because it is driving me crazy not making it right.
So if you're not able to help ... or say something about my equations because you dont know my way to use this method, dont say anything at all.
Someone who understands this kind of stuff can solve it easly and I'm sure I saw it in this forum. People have done that.

And yes obviously the current is controlling the dependent source and you didnt need multisim's schematic to know, is in the previous image.
I solved the circuit in about two minutes. I even told you what the power being delivered by the dependent source was so that YOU could check YOUR work.

You are convinced that your solution is wrong because it doesn't match the Multisim simulation.

I asked you to post your simulation and asked you if the simulation results are consistent with the original circuit.

You finally posted your Multisim simulation and I tried to draw your attention to a glaring difference between the original problem and your simulation circuit. But you aren't interested in even looking at it.

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