Physics307L:People/Cordova/Matt's Speed of Light Lab Summary
My partner for this lab was Sebastian.
The notebook for this lab can be found here.
Purpose
SJK 18:43, 28 October 2010 (EDT)
This is a good summary. A bit more discussion of difficulties encountered and possible improvements in the future would be good. I really appreciate the hard work you and Sebastian put in, in order to get good measurements!
- The purpose of this lab, as the name might suggest, is to calculate the speed of light by measuring the 'time of flight' (literally the time it takes light to travel a distance). Supposedly this lab yields a fairly accurate result, within a few percent of the accepted value.
Safety
- There will be a voltage source being used for this lab. Don't mishandle equipment/wires.
- The PMT receiver is sensitive. Do not expose it to room light when it is operational or it will be damaged.
Equipment
- PMT (photomultiplier tube)
- LED
- Oscilloscope TDS Tektronix 1002
- Bertan Power Supply Model 313B
- Canberra Delay Module NSEC 2058
- Ortec TAC/SCA Model 567 (time amplitude converter)
- Harrison Laboratories Power Supply model 6207A
- Multiple BNC Cables
- Long Carboard Tube
Set Up
- A detailed set up procedure can be found in Prof. Gold's lab manual. Basically, we connected the PMT to the TAC in order to read the time delay between when the LED sent out a pulse of light and when the PMT received this pulse as a voltage on the oscilloscope.
Results
The results for this lab are as follows:
[math]\displaystyle{ c_{best}=\frac{1}{slope}\frac{1}{10^{-2}}=31.26\frac{cm}{ns} }[/math]
[math]\displaystyle{ c_{low}=\frac{1}{slope+uncertainty}\frac{1}{10^{-2}}=30.95\frac{cm}{ns} }[/math]
[math]\displaystyle{ c_{high}=\frac{1}{slope-uncertainty}\frac{1}{10^{-2}}=31.58\frac{cm}{ns} }[/math]
The accepted value of c, according to Wikipedia is [math]\displaystyle{ c=29.98\frac{cm}{ns} }[/math], which is not within our range. We can say with a good amount of confidence that there was some systematic error. This could contribute to the fact that we were measuring the fastest quantity known in physics, which would require very accurate equipment. Also, although we accounted for time walk, it is still a possibility that this effected our results. All in all, however, we achieved a fairly accurate measurement of the speed of light, with a %error of less than 5%.
[math]\displaystyle{ %error=\frac{calculated-actual}{actual}*100=4.27% }[/math]
