Measuring the Speed of Light John Klumpp And Ainsley Niemkiewicz

Why Measure The Speed of Light? Inherently Difficult Electrodynamics Theory of Relativity Actually, We Don’t

How We Do It Measure Travel Time of Laser Pulse

Oscilloscope Setup Pros: Simple Straightforward Direct Cons: Less Accurate More Time Consuming

Electronic Circuitry Setup Pros: More Accurate Faster Cons: More Complicated Requires Calibration Many Components

Data Total Round Trip Distance: D AC = 62.71m Short Trip Distance: D AB =.486m Measured Flight Path Distance: D BC = 62.71m -.486m = m

Oscilloscope Data % AmplitudeAmplitude (mV)T AC (ns) 15% % % % % T AB, T BC, calculation of SoL with signal amplitude 136.4mV: % Amplitude Amplitude (mV) T AB (ns) T BC (ns) c (10 8 m/s) 15% % % % % (T BC = T AC – T AB, SoL = D BC /T BC = /T BC ) Total round trip flight time, including lag, TAC, with signal amplitude 138.8mV:

Electronic Circuitry Data Calibration: Time Calibrator Set to 40nS MCA Histogram Peaks at 2570mV and 2970mV Conclusion: 400mV=40ns  10mV=1nS

Measurement of T BC : Short Trip Peak at 510mV ~T AB Long Trip Peak at 2599mV ~T AC T BC ~ 2599mV – 510mV = 2089mV Applying Calibration Constant, T BC = 208.9nS We thus have c=d/t = m/208.9nS =2.979 * 10 8 m/S = c

Data Analysis Oscilloscope: Average of five measurements Uncertainty comes from -distance measurement -correlating peak locations C = (2.983±.05)*10 8 m/s % Error =.498%

Data Analysis Electronic Circuitry Electronic time measurements Computer analysis of data Very precise time measurements Uncertainty comes from: -distance measurement -Do we trust our equipment? C = (2.978±.03)*10 8 m/s % Error =.664%

Conclusion Classical Experiment, New Technology Accurate, Straightforward Method %Error < 1% Speed of light = speed of propagation of Maxwell’s EM waves! We can now test predictions of relativity