Light & Torches

Light, or visible light, is electromagnetic radiation of a wavelength that is visible to the human eye (about 400�700 nm). In a scientific context, the word light is sometimes used to refer to the entire electromagnetic spectrum. Light is composed of elementary particles called photons. In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. In thermodynamics, the quantity TdS is used as a representative measure of heat, which is the absolute temperature of an object multiplied by the differential quantity of a system's entropy measured at the boundary of the object. Heat can flow spontaneously from an object with a high temperature to an object with a lower temperature.