# Help homework for nodal analysis

#### ZAID12

Joined Jul 25, 2020
1

In this circuit it's asking for nodal analysis to find Vo/Vs

And that's where I stopped I need help because I don't know what to do next

#### WBahn

Joined Mar 31, 2012
26,067
You actually skipped a very important step.

Your first step in any analysis should be to write down all of your setup equations. Don't try to manipulate them yet, just write them down. Then draw a big line underneath them. This is the part of your work in which you translated a graphical representation of the problem into a mathematical one, so before you go any further, get in the habit of checking whether you did the translation correct because it is very difficult, and often impossible, to catch mistakes you made at this point later on because you are simply solving the system of equations that match a different problem.

Your node equation is nothing more than an application of KCL and each term represents a current flowing out of the node in question. So examine your node equation and ask whether each term represents a current flowing out of that node.

Next, you need to track your units throughout your work. Look at your second equation. You have in the numerator of the second term (A-Va). Well, 'Va' is a voltage and has units of voltage. But 'A' is a gain and doesn't have units at all. You can add or subtract two quantities unless they have the same units. What is the output voltage of that dependent voltage source? It's not 'A'. Get in the habit of checking whether your equations are dimensionally sound at each step. We all make silly mistakes and most of those mistakes will mess up the units. If we are tracking the units throughout our work we will catch most of those mistakes on the very line that we make them, and not after wasting a couple hours slogging through two pages of algebra coming up with an answer that was guaranteed to be wrong two pages ago.

#### RBR1317

Joined Nov 13, 2010
554
My first step in a nodal analysis is to identify the nodes & color code them. Then specify the currents in terms of these node voltages.

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