Physics307L:People/Young/Young's Oscilloscope

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Oscilloscope Lab Summary

SJK 01:17, 20 September 2008 (EDT)

01:17, 20 September 2008 (EDT)
This is a very good lab summary (except for the massive error in the formula used!). You do a good job summarizing what was done and presenting final results with uncertainty. As of yet, you still have things to learn about how to deal with uncertainty, but it's great that you included your estimate and an explanation. As for the error in formula, of course that is a huge deal in any of the subsequent labs. This could have been avoided by plotting the function in matlab, or looking at low time and infinite time limits, etc. I'm guessing this mistake will be easy to avoid in the future!


The purpose of this experiment was to explore the functions of the oscilloscope and become familiar with their operation and use in a lab setting through a series of measurements using a wave function generator. Some of the functions used in this lab were Basic Waveform Measurement, AC Coupling, Triggering, and digital storage. In addition to the previous we also found the fall time of our oscilloscope and used our fall time to find the time constant K which is equal to RC.

What I learned

I have dealt with Oscilloscopes before (both analog and digital) ,but only in very simplistic cases to measure voltage. I found that there was much to be learned about an oscilloscope beyond voltage measurements. As was stated in my notes, the triggering function is an extremely useful method for exploring the parts of a wave with a high time resolution. Closely viewing the waves can be helpful when attempting to acquire accurate readings for voltage or fall time as we found for the end of our lab.


10% fall time = 2.8±.05ms (.05ms is to account for human error since my eyes can only get cursor so close to the correct position

Starting Voltage= 22±.05V (Again .05 is to account for human error.)

Then to find the fall time constant I used my experimental values in the following equation.

[math]V(t) = V_0(1-e^{-\frac{t}{\tau}})\quad\iff\quad\frac{V(t)}{V_0}=(1-e^{-\frac{t}{\tau}})[/math]

[Fall Time Equation taken from here]

This is my matlab code solving for K (the time constant.)


K=0.3453<-----incorrect read further


SJK 00:59, 20 September 2008 (EDT)

00:59, 20 September 2008 (EDT)
Since the "summary" is more like a publication, I think it would be appropriate to delete your incorrect results in favor of the corrected ones. On the other hand, since it's not a formal publication, it's also OK to leave the incorrect result up there. Either way is OK -- my preference leans towards deleting it. Whereas in the raw data and raw analysis pages, it is a really good thing to leave the incorrect entries there (but to mark them clearly as incorrect too!)

Thanks to Dr. Koch's observations I realized that my equation for fall time was incorrect. The actual equation is K=-t./log(V./Vo) and so with the code corrected my actual value for K is

K =0.0228


SJK 00:56, 20 September 2008 (EDT)

00:56, 20 September 2008 (EDT)
It will be fun to come back and look at this after you've been through the next 6 labs, to see how much you will have learned about uncertainty! In any case, it's perfectly understandable that you're not well versed in it yet, and actually your intuitive method of just looking at the range of readings is a great start. It really does hit on the general purpose of uncertainty: "I am pretty confident the "true value" is in this range." And yes, we'll learn a few methods for how to do this quantitatively when we make a few assumptions about our errors and take careful measurements.

Overall my understanding of data analysis is minimal and therefore my uncertainty is based solely on the range in which the oscilloscope would fluctuate when giving me readings. The fall time falls within the range of the class average shown on Monday in our class(around 50ms). This leads me to believe that my measurement was close to the true value for my oscilloscope. The K found generally refers to RC. So to take this experiment even further we could find the Capacitance of the system knowing that the systems Resistance.