## DC Nodal Analysis Program

**What it teaches:** This program teaches the nodal analysis
method of solving DC electric networks. The basic idea is that applying Kirchhoff's Current Law at
the various nodes of the network yields a system of equations whose
simultaneous solution is the values of the node voltages. Here is a screen shot:

**How it works:** You draw an electric circuit by selecting various tools on the
toolbar and then clicking or dragging in the main drawing area in the middle of the screen.
Depending on the active button you can draw a piece of wire, a resistor, a current source, etc.,
or add, move, delete, change the value, direction, etc. of it.

When the circuit is complete, the program displays the nodes as red dots (and the supernodes as red lines) and you name the node voltages, which are the unknowns in the nodal analysis method. You may give some node voltage the name 0 (zero) and it then becomes the reference node.

The program then displays the system of equations and their solution. Here is a screen shot:

**Some ideas for teachers:**

- If you teach math, this application provides a good example of how systems of equations arise in
electrical engineering.
- If you teach electricity, then you can quickly show the effect of changing directions or
values of elements and of changing the reference node.
- You can show how the number of unknowns and the number of equations is affected by using
or not using a reference node, and by the presence of supernodes.
- You can set up homework and exam problems.

**Where to now?**