Open AccessAn undergraduate laboratory experiment to accurately measure the speed of light
Author(s) -
Andrew Murray
Publication year - 2020
Publication title -
european journal of physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.421
H-Index - 51
eISSN - 1361-6404
pISSN - 0143-0807
DOI - 10.1088/1361-6404/ab923f
Subject(s) - physics , speed of light (cellular automaton) , voltmeter , measure (data warehouse) , optics , beam (structure) , light beam , set (abstract data type) , amplitude , metre , electronics , laser , computational physics , electrical engineering , voltage , computer science , quantum mechanics , database , programming language , engineering
In 1983 the speed of light was set as an exact quantity. It is now one of the fundamental constants in physics, with the meter being directly related to this speed and the definition of the second. As such, experiments that calculate the speed of light with high precision are important in university undergraduate laboratories. In the experiment discussed here, a method is described that allows the speed of light to be calculated using an apparatus that fits onto a 1 m bench-top. An advantage of this method is that a simple digital voltmeter can be used. This measures the amplitude-modulated output from a laser beam emerging from a multi-pass cell that is mixed with that from a reference beam. The relative phase shift is determined as the modulation frequency changes, allowing the speed of light to be ascertained. Full details of the apparatus and the electronics designed for the experiment are presented.