Physics307L:People/Frye/SppedOfLight

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Speed of Light

SJK 21:29, 25 October 2010 (EDT)
21:29, 25 October 2010 (EDT)This summary is a bit thin, but on the otherhand, there's not a whole lot to summarize, so that's probably OK.  Comparison with accepted and discussion of systematic error could have been taken further. In combination with primary notebook, there was not enough description of your analysis methods.
21:29, 25 October 2010 (EDT)
This summary is a bit thin, but on the otherhand, there's not a whole lot to summarize, so that's probably OK. Comparison with accepted and discussion of systematic error could have been taken further. In combination with primary notebook, there was not enough description of your analysis methods.

This lab was performed in the senior laboratory in the UNM physics building on September 27th and October 4th with Alex Benedict

Summary and Results

For this experiment we followed the procedure of lab number 10 in Dr. Gold's lab manual.

We used a PMT, LED, and TAC to measure the time it took for a pulse of light to travel a distance. We started with the LED at some distance from the PMT. We then measured the voltage from the TAC, recorded it in our google docs spreadsheet then moved the LED closer and repeated.

On September 27, we moved the LED by 25cm each measurement and did 6 trials. We were still getting familiar with the technique on the first day so we did more runs the next week and changed the distance by less each measurement. On October 4, we moved the LED 10cm closer each time and did this 10 times to cover 1.0m each trial. We did 10 trials. We then did a linear fit of each trial to obtain the slope of the line. The we averaged the slopes from all 10 trials to obtain our final result. Our measured speed of light is 32.685 cm/ns +/- (2.448 cm/ns). The accepted value of the speed of light is 29.979 cm/ns SJK 20:51, 25 October 2010 (EDT)
20:51, 25 October 2010 (EDT)The final step here is to compare your discrepancy from the accepted speed (roughly 2.7 cm/ns) to the level of uncertainty (2.5 cm/ns).  You're slightly outside of the 68% confidence interval, but not too much.  However as will be noted elsewhere, I think you way overestimated your statistical uncertainty.Also, since you would find some systematic error, a discussion of possible sources and how to perhaps minimize it in the future would be warranted.Also, you have too many digits on your numbers.  There's some amount of personal preference, but your uncertainty will never have more than two digits of precision. So you would be better to write (32.7 +/- 2.5) cm/ns.
20:51, 25 October 2010 (EDT)
The final step here is to compare your discrepancy from the accepted speed (roughly 2.7 cm/ns) to the level of uncertainty (2.5 cm/ns). You're slightly outside of the 68% confidence interval, but not too much. However as will be noted elsewhere, I think you way overestimated your statistical uncertainty.

Also, since you would find some systematic error, a discussion of possible sources and how to perhaps minimize it in the future would be warranted.

Also, you have too many digits on your numbers. There's some amount of personal preference, but your uncertainty will never have more than two digits of precision. So you would be better to write (32.7 +/- 2.5) cm/ns.

Links

[Dr. Gold's Lab Manual]

My Lab Summary

Alex Benedict's Lab Summary

Alex Benedict's Lab Notebook

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