Physics307L F09:People/Andrego/Oscilloscope

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Brief Overview

SJK 23:02, 14 September 2009 (EDT)
23:02, 14 September 2009 (EDT)
This is a very good lab summary. You'll need to vary it for different labs, but I think you definitely have the idea of what I'm looking for in the informal lab summaries. I think you have a mistaken conception of the tau and expected value, which probably after reading what I wrote will be easily cleared up. Also, you should define "T" on this page, since the reader may not want to click through to your link. Overall, your primary lab notebook and summary were very good, and I think you and Anastasia did a very good job on this lab!

This lab focused on the uses and functions of the oscilloscope through procedures like measuring the fall-time of a sine wave through three different methods. Topics such as AC-DC Coupling were discussed, and I learned that the different modes of coupling depended on the the scale at which one wishes to observe shifts or ripples, in the smaller scale preference we discovered that the AC setting allows us to focus the screen more easily to the signal and hence see the ripples in the wave more easily. Other topics covered included the use of the trigger function, the "rising edge" of the wave, and the RC constant where we were able to compare the results on our oscilloscope screen with the examples described in the circuits web page that we consulted. We found that the RC constant we were looking at was RC<<T. When looking at the expected value of the fall-time "tau" (evaluated by using the equation -t/[ln(Vf/Vi)]=Tau) we discovered that our data varied largely from the expected value.

Data Results


  • With the Cursors = 50.4 ± 15 ms SJK 22:57, 14 September 2009 (EDT)
    22:57, 14 September 2009 (EDT)
    SAME NOTE COPIED FROM ANASTASIA'S SUMMARY: Kudos for reporting the measurement along with uncertainty! As I mentioned in class today, we'll spend the next couple months learning how to do this more and more rigorously. One very good thing about what you did is you very clearly discussed how you arrived at your uncertainty, so the read (me) could easily determine where your uncertainty statement came from. A final note, and we'll discuss this more in class: since your uncertainty was so large, you don't need the 3rd significant digit on your best guess value. So, it'd be better to say (50 +/- 15) ms
  • With the Measure Function = 83.8ms

Expected Value

SJK 22:51, 14 September 2009 (EDT)
22:51, 14 September 2009 (EDT)
Like I mentioned on your primary lab notebook page, I don't agree with the terminology "expected value." Rather, I think you mean "converted value," whereas the expected value would come if you happened to know what R and C were.
  • Tau=22.58 ms


My lab partner Anastasia and I had great difficulty getting consistent results from our oscilloscope readings. When we would use the measure function we noticed that our values were SIGNIFICANTLY larger than when we used the cursors. For this reason we noted in our oscilloscope lab notes that we did not trust these values at all. I believe that a lot of our relative error came from the fact that neither my lab partner nor I had ever used an oscilloscope before and hence we took a lot of time trying to figure out how to use the functions and read the screen. We were unable to complete enough trials to really get consistent data.