Ever since Galileo climbed a dark hill with a lamp, scientists have been experimenting with ways to measure the speed of light.1 Galileo’s method of sending a signal out to a distant hill and getting a response back did not prove accurate at the time. However, since the invention of lasers and oscilloscopes, this experimental method works well and provides fairly accurate results.2 In this paper, recent advances in technology are used to bring the experimental cost down to $100 while increasing the accuracy of the results to better than 3%.
Commercial systems, which use the Foucault method3 or a beam splitter,4 are available but are quite expensive. This method uses a modulated laser, modulation source, and detector as shown in Fig. 1. The output of the modulator and detector are compared on an oscilloscope. If an oscilloscope is not on hand, a basic model...
