Scales of Energy

Scientists measure the energies of fast-moving particles like those in cosmic rays and particle accelerators in units called electron volts, abbreviated eV. An electron volt is the amount of energy that one electron gains when it is accelerated by an electrical potential of one volt. (A flashlight battery has about 1.5 volts.) Electrons in a television set are accelerated by the picture tube to an energy of about 50,000 electron volts. When they strike the screen, they make it glow.

The most powerful man-made particle accelerator, Fermilab's Tevatron, can accelerate protons to nearly one trillion electron volts. The highest-energy cosmic ray particle ever observed had an energy 300 million times higher than the protons at the Tevatron. Scientific notation, shown below, saves writing out the many zeros required for such large numbers.