User:Randy Jay Lafler/Notebook/Physics 307L/Speed of Light Summary
The purpose for this lab was to measure the speed of light by using an LED to send photons across a tube to a PMT. We had to incrementally change the distance between the LED and the PMT, the distance the photon traveled, in order to generate a graph of travel time verse distance traveled. From this graph we calculated C as the inverse of the slope of the linear fit line. Link to my notebook
- We calculated C for two different data sets.
- This value we obtained from 16 measurements of the voltage as we decreased the distance by 10cm.
- This value we obtained for 8 measurements of the voltage, half as many as in data set 1, as we increased the distance back over the same distances by 20cm.
We obtained these values in the following way:
- At each distance we measured a voltage, and we converted the voltage to ns by the conversion: 1v=10ns.
- We then plotted time verse distance for each data point, and used the linest function in Excel to produre a linear fit to our graph.
- We calculated our best answer for C by inverting the slope, and we calculated our standard diviation by using the diviation in the slope given by Excel to calculate a range in C and subtracting the best answer from the high range. This assumes symmetric diviation, but it appears to be a good approximation.
The accepted value:
Thanks to Professor Koch and Katie for helping us understand the equipment and what we wanted to do, as well as explaining to us how to get time from our voltages. Emram for the pictures, graphs, and Excel sheet.