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Sunlight is the incandescence of the "white hot" surface of the Sun. Electromagnetic radiation from the sun has a peak wavelength of about 550 nm, [1] and can be harvested to generate heat or electricity. Thermal radiation can be concentrated on a tiny spot via reflecting mirrors, which concentrating solar power takes advantage of.
However, "heat" is a technical term in physics and thermodynamics and is often confused with thermal energy. Any type of electromagnetic energy can be transformed into thermal energy in interaction with matter. Thus, any electromagnetic radiation can "heat" (in the sense of increase the thermal energy temperature of) a material, when it is ...
Infrared radiation is popularly known as "heat radiation", [31] but light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun accounts for 49% [ 32 ] of the heating of Earth, with the rest being caused by visible light that is absorbed then re-radiated at longer wavelengths.
A diagram of the electromagnetic spectrum, showing various properties across the range of frequencies and wavelengths. The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band.
Radiative heat transfer is the transfer of energy via thermal radiation, i.e., electromagnetic waves. [1] It occurs across vacuum or any transparent medium ( solid or fluid or gas ). [ 15 ] Thermal radiation is emitted by all objects at temperatures above absolute zero , due to random movements of atoms and molecules in matter.
Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is not visible to human eyes. A portion of the thermal radiation from very hot objects (see photograph) is easily visible to the eye.
The radiation emitted covers the entire electromagnetic spectrum and the intensity of the radiation (power/unit-area) at a given frequency is described by Planck's law of radiation. For a given temperature of a black-body there is a particular frequency at which the radiation emitted is at its maximum intensity.
Bartoli in 1876 had derived the existence of radiation pressure from the principles of thermodynamics. Following Bartoli, Boltzmann considered an ideal heat engine using electromagnetic radiation instead of an ideal gas as working matter. The law was almost immediately experimentally verified.