ray, in physics, term denoting the straight line along which light or other form of radiation is propagated from its source. It generally refers to the line of propagation of waves but is also applied to streams of particles such as the electrons emitted from a cathode or particles emitted by substances exhibiting radioactivity. See cosmic rays; X ray.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.