Experimental special relativity with a meter stick and a clock

We present measurements of the velocity of electrons, performed with an apparatus using the time-of-flight method, to demonstrate that the speed of light c is the limiting speed for electrons. The results obtained show the applicability of relativity in a regime where nonrelativistic physics predicts velocities exceeding c. The main advantages of the apparatus are the simplicity of its operation and the data analysis. By using electrons from weak radioactive sources the experiment is suitable for the undergraduate laboratory. Furthermore, we show that with electrons from a linear accelerator and the same apparatus, excellent agreement between data and the relativistic expression for the speed of electrons in the keV-MeV energy range is observed. (C) 2009 American Association of Physics Teachers.