Science Series Video Archive

The Ultimate Speed

Dr. William Bertozzi - Massachusetts Institute of Technology

Sometime in 1962

In his youth, Dr. William Bertozzi, an MIT professor who has long been a leader in experimental nuclear physics using beams of electrons, carried out an experiment in which he explored the relationship between the velocity of electrons and their kinetic energy by measurements over a range of accelerating voltages between 0.5 MeV and 15 MeV. The kinetic energy is measured using calorimetry and the velocity is measured by time-of-flight. This educational film, made in 1962, documents the experiment and shows that the electrons have a limiting speed equal to that of light, in agreement with Einstein's theory of relativity.