Mathematics and Physics Glossary

Rad, n. (Phys.) A unit of energy absorbed from ionizing radiation, equal to 100 ergs per gram or 0.01 joule per kilogram of irradiated material.

Radian, n. (Math.) An arc of a circle which is equal to the radius, or the angle measured by such an arc. There are 2π radians in a full turn. There are π radians in 180°

Radiance, n. (Phys.) The radiant energy emitted per unit time in a specified direction by a unit area of an emitting surface. Also radiancy.

Radiant, a. (Phys.) Emitted or transmitted by radiation; as, a radiant energy; radiant heat.

-- Radiant energy, (Phys.) Energy given out or transmitted by radiation, as in the case of light and radiant heat.

-- Radiant heat, heat proceeding in right lines, or directly from the heated body, after the manner of light, in distinction from heat conducted or carried by intervening media.

-- Radiant point (Astron.) See Radiant.

Radiant, n.

1. (Opt.) The luminous point or object from which light emanates; also, a body radiating light brightly.