Measuring the speed of light using a webcam

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    Teachers from the University of Innsbruck named after Leopold and Franz (Austria) offered students an updated installation for experiments on measuring the speed of light. It uses a laser, a rotating mirror from the printer, a webcam that catches the reflected light beam and a program for calculating the results.

    In the classic Foucault experiment on measuring the speed of light, a candle was used as a light source, and two mirrors were used to measure it. One mirror rotated quickly, the light reflected by it fell on the second, having a concave shape, and then returned back to the first. During the travel of light, the mirror managed to turn a certain angle, measuring which, we can calculate the time for which the light twice passed the known gap between two mirrors.

    Now the necessary equipment for such an experience can be bought on the Internet . Instead of a candle, a laser is used there. But university teachers decided to go further and introduce modern technology into their experience.

    “Among other things, we teach students how to handle image processing,” explains Gregor Weiss , one of the initiators of the experiment. - We get a good accuracy of the experiment, so we encourage students to search for those equipment imperfections that introduce error into the results. It’s very useful to check assumptions and think what could have gone wrong in real experience compared to schemes and theory. ”

    In the classical scheme of measuring the results of the experiment, mechanical means of measuring lengths and angles are used, and therefore the accuracy of these measurements leaves much to be desired - the result may differ from the known value by 5%. In the updated experiment, accurate measurements allow us to obtain an answer that differs from the standard by no more than 1%.

    Well, for those who want to measure the speed of light, even if not so accurately, but inexpensively, I propose using the well-known experience with a chocolate bar and a microwave. If you slightly warm the chocolate without rotation, then the distance between the centers of melting (about 6 cm) will be half the wavelength. If we multiply the wavelength of 12 cm by the frequency of the microwaves (it is indicated on the plate on the back of the microwave, and usually is 2.45 GHz), then we get a speed of 2.94 * 10 10cm / s, which is close enough to the real speed of light 2.9979 * 10 10 cm / s.

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