(Such behaviour is typified by water waves in the way they propagate and periodically reinforce and cancel one another.) Matter rays, on the other hand, were considered to be inherently particle-like in character-i.e., localized in space and incapable of interference. In the discussion that follows, those of the first category are referred to as “electromagnetic rays” (plus the neutrino) and those of the second as “matter rays.”Īt one time, electromagnetic rays were thought to be inherently wavelike in character-namely, that they spread out in space and are able to exhibit interference when they come together from two or more sources. In short, the two broad classes of radiation are unambiguously differentiated by their speed of propagation and corresponding presence or absence of rest mass. When such forms of particulate matter travel at high velocities, they are regarded as radiation.
In a state of rest, these particles have mass and are the constituents of atoms and atomic nuclei. The second type includes such particles as electrons, protons, and neutrons. These are all characterized by zero mass when (theoretically) at rest. The first type constitutes the spectrum of electromagnetic radiation that includes radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X rays, and gamma rays, as well as the neutrino (see below).
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Radiation may be thought of as energy in motion either at speeds equal to the speed of light in free space-approximately 3 × 10 10 centimetres (186,000 miles) per second-or at speeds less than that of light but appreciably greater than thermal velocities (e.g., the velocities of molecules forming a sample of air). Observe how radiation from atomic bombs and nuclear disasters remains a major environmental concern See all videos for this article SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.
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