Physics307L:People/Wilkinson/SpeedofLight

Speed of Light Summary

Steve Koch 01:17, 22 December 2010 (EST):The notes here are very thin and would seriously preclude any kind of reproducibility.

Motivation

The speed of light is one of the fundamental constants in nature. Indeed, its importance spans from general relativity to quantum mechanics making an appearance in many physics equations. Einstein was the first to not that the speed of light is something special. He showed, through his theory of special relativity, that the speed of light is the largest speed anything can travel through space. The basis of this lab is to measure the speed of light in a basic laboratory setup.

Theory

The theory behind this lab is very simple. We prescribe a distance between a LED and a detector and measure the time it takes a light pulse to traverse the distance.
[math]\displaystyle{ c = \frac{L}{t} }[/math]
The distance is measured with a meter stick. The time derived from measuring a voltage off of an oscilloscope. See the Lab Notebook for further details on how the voltage is measured.

Data

The data was analysed using Google Docs and the linest function. Here is the data taken and the subsequent analysis.

{{#widget:Google Spreadsheet |key=0AunM4cHOH1N7dENZdXAwUHBOMWZTVl9BN29wb2VjVEE |width=900 |height=400 }}

Results

I report the speed of light as [math]\displaystyle{ 28(6) \frac{cm}{ns} }[/math].

Error

There is a large amount of error in this lab. The data was not taken very well and quite honestly I don't think we knew what we were doing. The three runs have very different results the first run gave the best result at [math]\displaystyle{ 28(6) \frac{cm}{ns} }[/math]. The other two were [math]\displaystyle{ 40(9) \frac{cm}{ns} }[/math] and [math]\displaystyle{ 80(8) \frac{cm}{ns} }[/math]. Obviously these results vary WIDELY and have no correlation with one another. Therefore, I rest my case that this lab was a failure.