# Homework Help: Need help finding node equations

1. Feb 22, 2012

### elec_eng

Need help finding node equations!!

[url=http://www.0zz0.com][PLAIN]http://www11.0zz0.com/2012/02/22/06/267083816.jpg[/url][/PLAIN]

I need to find the node equations for node voltages 1 and 3 to find voltages V1 and V3 leaving R3 as a variable!

hope to get help soon!
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 22, 2012

### tiny-tim

welcome to pf!

hi elec_eng! welcome to pf!

show us what you've tried, and where you're stuck, and then we'll know how to help!

(btw, please don't post such wide pictures!)

3. Feb 22, 2012

### elec_eng

Re: Need help finding node equations!!

This is what i tried!
(v1-v4)/R1+ (v1-v3)/R4=0
(v3-v2)/R4+ (v3-v1)/R3+ (v3-v4)/R5= 0

4. Feb 22, 2012

### Staff: Mentor

Re: Need help finding node equations!!

Those equations don't appear to match the circuit. Perhaps you're not correctly identifying everything that comprises the individual nodes? Presumably the first equation is supposed to pertain to NODE 1? If so, what path does the second term describe? Where is the path from NODE 1 to NODE 2?

If the second equation pertains to NODE 3, then the last term is incorrect; it describes a path from NODE 3 to NODE 4 via resistor R5, but this path doesn't exist. Resistor R5 terminates at NODE 0 (Ground).