Lab 2A: Superposition Experiment
Note: This part of the lab is just to develop your intuition about superposition. There are no responses that need to be checked.
Circuits with multiple sources can be hard to analyze as-is. For example, what is the voltage between the two terminals on the right of Figure 1?
Figure 1. Example multi-source circuit
We can use superposition to make the analysis much easier. The circuit in Figure 1 can be decomposed into two separate subcircuits: one involving only the voltage source and one involving only the current source. We'll analyze each circuit separately and combine the results using superposition. Recall that to decompose a circuit for analysis, we'll pick each source in turn and set all the other sources to zero (i.e., voltage sources become short circuits and current sources become open circuits). The circuit above has two sources, so the decomposition produces two subcircuits, as shown in Figure 2.

(a) Subcircuit for analyzing contribution of voltage source | (b) Subcircuit for analyzing contribution of current source

Figure 2. Decomposition of Figure 1 into subcircuits
Let's use the DC analysis capability of the schematic tool to see superposition in action. The sliders below control the resistances of R1, R2, R3 and R4 in all the diagrams. As you move the sliders, the schematic tool will adjust the appropriate resistance, perform a DC analysis and display the node voltages on the diagrams. Here's what you want to observe as you play with the sliders:

The voltage for a node in Figure 1 is the sum of the voltages for that node in Figures 2(a) and 2(b), just as predicted by superposition. (Note that due to round-off in the display of the voltages, the sum of the displayed voltages in Figure 2 may only be within .01 of the voltages displayed in Figure 1.)

R1 |
R2 |
R3 |
R4 |