It is the most basic form of heating known to man. Used by cavemen to heat themselves by fires; by Romans in their hypocausts, by log burners and tile stoves, Infrared heating has been favoured for millennia because like the heat of the sun on your surrounding environment — even during winter — Infrared heats objects, which then radiate back and keep the environment warm around you.
Radiant heat does not heat air — which holds little heat and rapidly disperses. Infrared waves travel through the air and when they touch a surface, heat energy is released regardless of the surrounding air temperature.
That heat energy excites the molecules in the object it meets which being to vibrate and gain energy and warm up. Far Infrared — unsurprisingly — the same band of infrared that the human body itself emits.
Everything with a temperature above around 5 degrees Kelvin minus degrees Fahrenheit or minus degrees Celsius emits IR radiation. The sun gives off half of its total energy as IR, and much of the star's visible light is absorbed and re-emitted as IR, according to the University of Tennessee. Household appliances such as heat lamps and toasters use IR radiation to transmit heat, as do industrial heaters such as those used for drying and curing materials.
Incandescent bulbs convert only about 10 percent of their electrical energy input into visible light energy, while the other 90 percent is converted to infrared radiation, according to the Environmental Protection Agency.
Infrared lasers can be used for point-to-point communications over distances of a few hundred meters or yards. The receiver converts the light pulses to electrical signals that instruct a microprocessor to carry out the programmed command. One of the most useful applications of the IR spectrum is in sensing and detection. All objects on Earth emit IR radiation in the form of heat. This can be detected by electronic sensors, such as those used in night vision goggles and infrared cameras.
A simple example of such a sensor is the bolometer, which consists of a telescope with a temperature-sensitive resistor, or thermistor, at its focal point, according to the University of California, Berkeley UCB. If a warm body comes into this instrument's field of view, the heat causes a detectable change in the voltage across the thermistor. Night vision cameras use a more sophisticated version of a bolometer.
These cameras typically contain charge-coupled device CCD imaging chips that are sensitive to IR light. The image formed by the CCD can then be reproduced in visible light. This being said, the reason why IR light is produced and associated with heat is that you are seeing molecules go from one vibrational quantum state to a lower vibrational quantum state by giving off a photon of appropriate energy in the IR region.
Note that vibrational states are only really accessible at higher near room temp generally temperatures. All matter in bulk radiates approximately as a black body radiator , approximately because there are coefficients of emissivity depending on the constituents.
For gases the functional form is different. The radiation has a specific spectrum and intensity that depends only on the temperature of the body. As the temperature decreases, the peak of the black-body radiation curve moves to lower intensities and longer wavelengths. The black-body radiation graph is also compared with the classical model of Rayleigh and Jeans. Heat may be defined as energy in transit from a high temperature object to a lower temperature object.
An object does not possess "heat"; the appropriate term for the microscopic energy in an object is internal energy. The internal energy may be increased by transferring energy to the object from a higher temperature hotter object - this is properly called heating. The energy loss by a black body is given by the Stefan-Boltzman law. Thus the energy carried away by the infrared radiation reduces the heat content of the radiating body.
This is the connection of infrared to heat. The microscopic interactions that give rise to the photons are explained in the other answers. This answer concerns the thermodynamic framework. I think I understand your confusion. The answer would be: You've been misguided. There is no special link between heat and infrared radiation, except for the fact that most bodies radiate most of their heat in the infrared spectrum because they don't have enough energy heat to radiate at a higher frequency.
See the graphs in this thread. So one could claim the same connection between X-rays and heat. In fact, it would be even more so, since interactions with X-rays are even higher energy, except that there aren't that many things radiating x-rays around.
The easiest answer is that below 3, Kelvin in temperature, heat radiates EM often referred to as light by physicists although it is all EM not just visible light in the infrared. Because most heat generates light in the infrared, scientists often refer to infrared light as heat.
This is a generalized term or a convention. Technically heat energy and light are different things, but heat energy can be measured by its EM radiation.
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