Circuit Problem: Nodal Analysis

[jmcoreymv]

I have to find Vo in this circuit
here
using nodal analysis.

I cant seem to figure out how. I wrote the KCL equations at node V1:
(V1-Vo)/3 + (V1-3)/1 = (4Vo-V1)/5
The current through the 3 ohm and the 2 ohm resistor should be equal so I wrote (Vo-V1)/3 = -V0/2

I solve those and I always end up getting a different answer and I cant figure out what Im doing wrong. Any ideas?

 

[Orsorum]

I found Vo last night. She was hootttt.

 

[cressida]

Originally posted by: jmcoreymv
I have to find Vo in this circuit
here
using nodal analysis.

I cant seem to figure out how. I wrote the KCL equations at node V1:
(Vo-V1)/3 + (V1-3)/1 = (4Vo-V1)/5

The current through the 3 ohm and the 2 ohm resistor should be equal so I wrote (Vo-V1)/3 = -V0/2

I solve those and I always end up getting a different answer and I cant figure out what Im doing wrong. Any ideas?

you have to use nodal? You can solve with other stuff easily, but let me give this thing a try

 

[jmcoreymv]

Yep unfortunately I have to use nodal. And it is just giving me a headache.

 

[Gibson486]

Are you using a green circuits book called Intro to circuits for Computer and Electrical engineers? I think i did that same exact problem 2 nights ago, but i think i answered it wrong also.

 

[NutBucket]

i think you've got your equations backwards or something. But yeah, I would use mesh if I was you.

 

[jmcoreymv]

The book is fundamentals of electric circuits, second edition. We dont learn mesh analysis till next week, and I have to learn to solve it with nodal because I know she will ask for it on the midterm.

 

[RaynorWolfcastle]

I did a quick mesh analysis and came up with Vo = 30/29, I may have made a math mistake though as my RREF skills are somewhat lacking 😛

 

[jmcoreymv]

My friend came up with 6/5, Ive come up with 10/9 and various other fractions where the numerator is 1 more then the denominator.

 

[cressida]

Here are the formulas I got (it's been a while so I might totally off)

for Node V1: (V1 - V0)/2 + (V1 - 3) + (V1 - 4V0) / 5 = 0
for Node V0: (V0 - V1)/3 + (V0)/2 = 0

My answers:
V1 = 25/9
V0 = 10/9

let me double check, I hate my algebra

 

[NutBucket]

That sounds right, but I think V1 should be (V1-V0)/3 + (V1-3) + (V1-4V0)/5=0

 

[jmcoreymv]

Originally posted by: Synergy
Here are the formulas I got (it's been a while so I might totally off)

for Node V1: (V1 - V0)/2 + (V1 - 3) + (V1 - 4V0) / 5 = 0
for Node V0: (V0 - V1)/3 + (V0)/2 = 0

My answers:
V1 = 25/9
V0 = 10/9

let me double check, I hate my algebra

Thats what I got...awesome.

 

[RaynorWolfcastle]

I rechecked with nodal, 10/9th is right, lemme recheck my meshes. Found a sign mistake in my RREF, 10/9 is verified by mesh analysis as well.

 

[cressida]

Originally posted by: jmcoreymv

Originally posted by: Synergy
Here are the formulas I got (it's been a while so I might totally off)

for Node V1: (V1 - V0)/2 + (V1 - 3) + (V1 - 4V0) / 5 = 0
for Node V0: (V0 - V1)/3 + (V0)/2 = 0

My answers:
V1 = 25/9
V0 = 10/9

let me double check, I hate my algebra

Thats what I got...awesome.

Not even a thanks :frown:

oh well time for more HW :beer:

 

[jmcoreymv]

Haha thanks, got another if you want to practice....

 

[BullsOnParade]

for Node V1: (V1 - V0)/2 + (V1 - 3) + (V1 - 4V0) / 5 = 0
for Node V0: (V0 - V1)/3 + (V0)/2 = 0

the (V1-3) part doesn't make any sense. basically when you
do node analysis you are doing currents going into or out of
the nodes. V1-3 itsn't a current so that equation is fud.

~bulls

 

[cressida]

Originally posted by: BullsOnParade
for Node V1: (V1 - V0)/2 + (V1 - 3) + (V1 - 4V0) / 5 = 0
for Node V0: (V0 - V1)/3 + (V0)/2 = 0

the (V1-3) part doesn't make any sense. basically when you
do node analysis you are doing currents going into or out of
the nodes. V1-3 itsn't a current so that equation is fud.

~bulls

When you do the equation for V1 - 3 you notice the ohm value 1 (V1 - 3)/1 so what is something over 1? Back to basics for you 😛

 

[tigerbait]

whoa..I totally don't remember how to do that.... graduated from EE in 2002, took circuits I back in 2000.... I better start studying for my PE now.

😱

after reading this thread, though, it came back to me a little bit.... never have to do anything like this at work though... thank goodness for ETAP and Aspen.

 

[jmcoreymv]

So if I ever graduate as an EE, I wont have to worry about doing this sort of stuff? Awesome....