# Node-Voltage Analysis

Discussion in 'Homework Help' started by Teszla, Jun 19, 2013.

1. ### Teszla Thread Starter Member

Jun 7, 2013
43
0

I'm wondering here, when writing an expression for Vx, I had assumed that it would correct to say that

$V_{x}=\frac{V_{3}-V_{1}}{R_{1}}$

Why is this not correct in this case?

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
It's not correct because the units for (V3-V1)/R1 would be ampere not volt. Surely Vx is simply (V3-V1).

3. ### Teszla Thread Starter Member

Jun 7, 2013
43
0
Ah yes of course... seems sometimes the logical part of my brain is turned off...

4. ### WBahn Moderator

Mar 31, 2012
18,079
4,917
You need to get in the habit of always, always, ALWAYS checking if the units work out. Always. I can't even begin to count how often I catch mistakes because the units aren't working out. Sometimes is a math goof, sometimes my thinking about the problem when I set it up is flawed, sometimes I go off on a tangent and start solving for something other than what I intended. But the vast majority of these mess up the units.

If you get in that habit (and it truly becomes an ingrained habit in short order), you will look at the above equation and immediately gasp thinking, "Voltage equals Current!? WRONG! WRONG! WRONG!" Far better that happen on line six than on line twenty-six.