*Update: Solved :)

[QueHuong]

I've been sitting and staring at this problem for a while, and can't actually get it. I can do the math (if it comes out to be a simultaneous linear equation problem), but I need help with setting it up.


How do I find the currents through R2, R4 and R5 for node 4 and currents through R2. R3, R4 through node 5 using Kirchoff's Laws?
The problem


Thanks. This is precisely why I'm not an electrical engineer.

 

[cressida]

k hold on ... I don't want to do this doing nodal analysis, it sucks.

 

[SaturnX]

K, well the easiet approach is going to be Loop analysis, I'm far too lazy to actually write it all out, but basically you do this:

Assign arbitary currents for each of the three loops, lets say, i1,i2,i3 going clockwise.

Now using KVL, write out the expressions of each resistor/powersupply as you come to them, the only trick is that along the line where you have teh 9V source, the current throuh that strech would be (i3 - i1) since you've assigned them to be clockwise, and the same would apply to the i2 block along the top, the current through R4 would be (i2 - i1)

Once you do all that, simplyfy all your expressions, and you end up with a linear set of equations, now just solve 🙂

Edit: Oh yeah, and through R3 the current would be (i2 - i3). Remember it's all arbitrary, just stick to one notation with your currents and you're golden.

And to clarify what I'm talking about: Circuit Diagram Edited

--Mark

 

[cressida]

Originally posted by: SaturnX
K, well the easiet approach is going to be Loop analysis, I'm far too lazy to actually write it all out, but basically you do this:

Assign arbitary currents for each of the three loops, lets say, i1,i2,i3 going clockwise.

Now using KVL, write out the expressions of each resistor/powersupply as you come to them, the only trick is that along the line where you have teh 9V source, the current throuh that strech would be (i3 - i1) since you've assigned them to be clockwise, and the same would apply to the i2 block along the top, the current through R4 would be (i2 - i1)

Once you do all that, simplyfy all your expressions, and you end up with a linear set of equations, now just solve 🙂

Edit: Oh yeah, and through R3 the current would be (i2 - i3). Remember it's all arbitrary, just stick to one notation with your currents and you're golden.

And to clarify what I'm talking about: Circuit Diagram Edited

--Mark

what he says . 😉

 

[shuan24]

following this example, I get the following equations:

V1 - I1(R1 + R3) - V2 + I2R1 + I3R3 = 0
V2 - I2(R1+ R2+ R4) + I3R4 = 0
-I3(R3 + R4 + R5) + I1R3 + I2R4 = 0

From there you have 3 equations and 3 unknowns...you should be able to solve for the respective currents. (I used the top box as I2, bottom left box as I1, and bottom right box as I3) Good luck.

 

[sharkeeper]

Thanks. This is precisely why I'm not an electrical engineer.

Sorry but if you always ask for help for these problems how do you expect to make it in the real world?

 

[shuan24]

uh even real electrical engineers need real help in the real world.

 

[BigJelly]

Originally posted by: sharkeeper

Thanks. This is precisely why I'm not an electrical engineer.

Sorry but if you always ask for help for these problems how do you expect to make it in the real world?

My guess would be by avoiding eletrical circuits or as he stated "not being an electrical engineer" FYI people can go through life without being able to answer these problems

 

[sharkeeper]

My guess would be by avoiding eletrical circuits or as he stated "not being an electrical engineer" FYI people can go through life without being able to answer these problems

Just wait until deleted is out in full force. Asking for homework publicly without consent of the professor results in an instant zero for the assignment.

 

[shilala]

Originally posted by: sharkeeper

Thanks. This is precisely why I'm not an electrical engineer.

Sorry but if you always ask for help for these problems how do you expect to make it in the real world?

I do it just like he did it. I ask someone who knows the answer.
It's really neat. People ask me a lot of questions, and when I know the answer I give it to them.
It's fvckin awesome. I think they call it "help".

 

[sharkeeper]

I do it just like he did it. I ask someone who knows the answer.
It's really neat. People ask me a lot of questions, and when I know the answer I give it to them.
It's fvckin awesome. I think they call it "help".

Let me give you folks a little hint. You learn to troubleshoot by working the problem. Asking for help every time you're stumped is cheating yourself. This is clearly a homework assignment.

Too many times people come in here and ask for help and they get an answer - not always correct too! - so what is learned?

Sure it's ok to ask for help in the real world. IT guys have it easy because most of them don't solve problems - they "win" by being able to find the answer the fastest. If terrorists want to hurt the US, they should attack Google I swear to God.

 

[mrrman]

Originally posted by: SaturnX
K, well the easiet approach is going to be Loop analysis, I'm far too lazy to actually write it all out, but basically you do this:

Assign arbitary currents for each of the three loops, lets say, i1,i2,i3 going clockwise.

Now using KVL, write out the expressions of each resistor/powersupply as you come to them, the only trick is that along the line where you have teh 9V source, the current throuh that strech would be (i3 - i1) since you've assigned them to be clockwise, and the same would apply to the i2 block along the top, the current through R4 would be (i2 - i1)

Once you do all that, simplyfy all your expressions, and you end up with a linear set of equations, now just solve 🙂

Edit: Oh yeah, and through R3 the current would be (i2 - i3). Remember it's all arbitrary, just stick to one notation with your currents and you're golden.

And to clarify what I'm talking about: Circuit Diagram Edited

--Mark

Exactly what I was thinking...I even had the diagram in my mind...good one Mark

 

[QueHuong]

Thanks all. I understand it now. :thumbsup:

Originally posted by: sharkeeper

Thanks. This is precisely why I'm not an electrical engineer.

Sorry but if you always ask for help for these problems how do you expect to make it in the real world?

Unless you've gotten through life without ever needing help and you're actually successful, then you can talk - but people like that doesn't exist. Since talkers like you get ignored in real life, I'm going to do the same.

 

[SaturnX]

Originally posted by: mrrman

Originally posted by: SaturnX
K, well the easiet approach is going to be Loop analysis, I'm far too lazy to actually write it all out, but basically you do this:

Assign arbitary currents for each of the three loops, lets say, i1,i2,i3 going clockwise.

Now using KVL, write out the expressions of each resistor/powersupply as you come to them, the only trick is that along the line where you have teh 9V source, the current throuh that strech would be (i3 - i1) since you've assigned them to be clockwise, and the same would apply to the i2 block along the top, the current through R4 would be (i2 - i1)

Once you do all that, simplyfy all your expressions, and you end up with a linear set of equations, now just solve 🙂

Edit: Oh yeah, and through R3 the current would be (i2 - i3). Remember it's all arbitrary, just stick to one notation with your currents and you're golden.

And to clarify what I'm talking about: Circuit Diagram Edited

--Mark

Exactly what I was thinking...I even had the diagram in my mind...good one Mark

Haha, thanks, it seems I actually learned something in 1st year EE hahah.. 😉

--Mark