# Nodal Analysis - No Resistor

Discussion in 'Homework Help' started by p75213, Aug 26, 2011.

1. ### p75213 Thread Starter Member

May 24, 2011
39
0
I am having problems with this circuit. The circuit has 3 nodes - v1,v2 and v3. Solve for the voltage across the 3 ohm resistor using nodal analysis. the 3 equations I get are as follows:
1) (v1-v3)/6-2+(v1-v2)/4+v1/0=0
2) (v2-v1)/4+v2/0+(v2-v3)/2=0
3) (v3-v1)/6+2+(v3-v2)/2+v3/3=0
This is obviously wrong. The 1st equation has v1/0 and the second equation has v2/0. How do I get rid of them?
Can somebody help with this please?

File size:
7.7 KB
Views:
82
2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Just to clarify your schematic. Is the earth [0V] connected to both the bottom "rung" and the center of the first "rung"?

3. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,993
1,116
Simply ignore V3
Write the nodal equation only for V1 and V2

File size:
13.9 KB
Views:
63

May 24, 2011
39
0
yes it is.

May 24, 2011
39
0
Yes it is.

May 24, 2011
39
0

7. ### p75213 Thread Starter Member

May 24, 2011
39
0
Is there no current through v3? Ignoring v3 I get:
1) (v1-v2)/6-2+v1/0=0
2) (v2-v1)/6+2+v2/3=0

I still have a divide by 0 in 1). Can v1/0 be replaced by -v2/3?

8. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
It would be useful for you to re-draw the schematic taking account of which elements are connected to the common [0V] rail. You'll find that apart from the common node there is only one other node.

9. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,993
1,116
Ok so the diagram look like this

And we only have one unknown node voltage V1.

File size:
13.2 KB
Views:
134