Before working in any labs or class examples, we first set up accounts for everycircuit. In order to test our understanding of the program, we were instructed to create a sample circuit in everycircuit:
Lab 11: Thevenin's Theorem
In this lab, we analyzed a circuit to determine its Thevenin equivalent, then we experimentally determined the Thevanin resistance and the open-circuit voltage necessary to create the Thevenin equivalent circuit. We were then able to change the load resistance to determine the voltage and power given various resistances for the following circuit:
For the pre-lab, we first analytically determined the Thevenin equivalent resistance and voltage.
By removing the two power sources from the loop and adding up the resistors, we were able to easily determine the Thevenin resistance of 7.4 kOhms. Thevenin voltage was determined to be 54 mV using current loops.
In order to double check our results, we recreated the circuit in the Everycircuit program
According to this diagram, the voltage drop across the 1k resistor was 2.82V - 2.77 V = 50mV. The sig figs don't precisely match our results, but it can be seen that our analysis was at least in the ballpark of the true Thevenin voltage.
The picture below is a table we created of the resistors used. On the left are the resistors chosen, and on the right are the actual values of those resistors.
Below is a picture of the experimental circuit we built for this lab:
Pictured below is the multimeter reading across the 1k resistor:
The result shown in the multimeter confirms our prediction of 54 mV. The multimeter reads 52.3 mV, which is very close, but probably slightly off due to the error in the resistors, as well as internal resistance in the breadboard, wires, and the multimeter itself.
After confirming the Thevenin resistance and voltage, we replaced the 1k resistor between nodes a and b with a 10k potentiometer. Unfortunately, our pot only went up to 8.7k, but the results are shown in the table below:
We tested the voltage for every 1k resistor value up to 8.7k. The power values were calculated using the equation P = V^2/R.
Below is a graph of power vs. resistance according to the values obtained through this lab.
In-Class Exercises:
1. Find the Thevenin Equivalent as seen by R below
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