Physics307L:People/Carrillo/Speed of Light

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Speed of Light Lab Summary

SJK 12:33, 22 October 2010 (EDT)
12:33, 22 October 2010 (EDT)
The scope of this summary is good. The main things missing, which are very important, are the uncertainty and statistical comparison with the accepted value, as noted below.

Brief Overview

The purpose of this lab was to measure the speed of light, Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle c\,\!} . To measure this, we used pulses from an LED light with a high speed detector and a delay module in a direct time of flight measurement over varied distances. The PMT, TAC module, and the o-scope helped us succeed in making mearurements for this lab. We graphed the voltage readings from the o-scope versus the distances between the PMT and LED light, and therefore we were able to calculate the speed of light by finding the best fit linear slope.

Our Data Results

SJK 12:32, 22 October 2010 (EDT)
12:32, 22 October 2010 (EDT)
See your primary notebook for comments about the analysis. For here, let's assume your numbers are correct. Here's how to improve this section: First, you need uncertainty on your measurement. Assuming your uncertainty was, say 0.5 cm / ns, you would want to trim a bunch of digits from your best value. You would write it (11.7 +/- 0.5) cm / ns. Then, to compare with the accepted value, you would compare your discrepancy (about 18 cm / ns) with your uncertainty (0.5 cm / ns). You would see that you are something more than 30 times further from the accepted value than your standard error of the mean. This would mean for sure that you have huge systematic error. This is the way to compare with the accepted value--the relative error that you calculate below is not as important, and not very meaningful without an estimate of uncertainty.
Our average measured value of the speed of light is...
  • Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle c_{measured, average}=11.69289469\frac{cm}{ns}\,\!}
The accepted value of the speed of light from Wikipedia is...
  • Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle c_{accepted}=29.98\frac{cm}{ns}\,\!}

Error

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle \% error=\frac{c_{accepted}-c_{measured, average}}{c_{accepted}}\,\!}

therefore our percent error is...

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle \simeq61%\,\!}
  • Please see the section about our error in my lab notebook.

Conclusion

In conclusion, I learned a lot from this lab and I thought that the lab was really interesting. The hardest part of this lab to me was getting started with the setup and figuring out what types of settings we needed to have for the equipment. We did not get a close value to that of the accepted value of the speed of light, so therefore we got a pretty bad percent error. If you would like to see the reasons for this error please click on the link above in the error section. Perhaps we did not really understand the concept of timewalk, which may have given us bad data.SJK 12:33, 22 October 2010 (EDT)
12:33, 22 October 2010 (EDT)
I think you learned a lot about the equipment, and with more time, probably would have obtained better data. Please see Ginny's pages for some more comments.