Based on the discussions in class that I intended to preceed this RC lab it became apparent that it might be valuable to actually construct a prelab activityto provide some insight into the meaurements you will be expected to make the following week.b
Purpose:
To explore the relationship between what we calculate/analyze in an academic setting and what that looks like in the wild where the resistors and capacitors are not some Purdue like object but rather free range devices with a mind of their own.
We analyzed the following circuit when the impedance of the capacitor was much less than, equal to, and much greater than the impedance of the resistor.
Procedure:
1) Wire the illustrated circuit on a small project board. We will use the function generator as the power supply. Be careful to define a clear ground point in your circuit layout as well as where you will connect the function generator. After having the circuit verified by the instructor you may set up the function generator and begin your measurements.
You will be making measurements of the input waveform and the output waveform. If you can do these both simultaneously it will make things go quicker. To accomplish this you will need to use both "channels" or inputs on your oscilloscope simultaneously. There are some additional settings you will need to check and set to make this happen. Check with your lab instructor if you have questions.
2) Set up your function generator to provide a 3 V peak to peak sine function at an w of 1 kHz. Use the oscilloscope to verify this set up. Determine the capacitance that you need so that the impedance of the capacitor and the resistor are equivalent. Calculate the expected AC voltage across the resistor under these circumstances. Locate the appropriate capacitance and replace the capacitor currently in your circuit.
3) Measure and observe the output voltage across the "load" resistor and determine the phase shift between the source and the load. You should have a clear expectation for both the amplitude and the phase shift of the load voltage from the previous step. Sketch the traces you observe on the scope and indicate the amplitudes and phase relationships.
4) Explore how the phase and the amplitude of the load voltage change as you change the frequency of the source. How does this relate to the plot you generated for the first part of this lab?
5) Repeat steps 2 and 3 using capacitors 10 times larger and smaller than the one you originally used. Determine and sketch the amplitude and phase relationships that you observe in these two cases. You do NOT need to repeat step 4 unless you wish to.
6) Determine the capacitance of an unknown capacitor using your circuit. Document your data and your calculations that lead to your conclusion and discuss the accuracy with which you can make this determination.
Lab "Notebook":
The following information should be clearly presented in your lab "notebook" along with explanatory and insightful commentary.
I) A clear drawing of the circuit constructed including the connections to the function generator and oscilloscope.
II) Show how you calculated/determined the value of the capacitance that matched the impedance of the resistor.
III) Representative sketches of the output signals observed at various points in the process..
IV) Think about and articulate your understanding of the difference between a capacitive load and a resistive load in the context of this lab. What would you expect for a circuit which has an inductor in parallel with a resistor?
V) Present your results for the determination of the unknown capacitance.
