Leslie's cube is a device used in the measurement or demonstration of the variations in thermal radiation emitted from different surfaces at the same temperature.
Leslie's cube is a device used in the measurement or demonstration of the variations in thermal radiation emitted from different surfaces at the same temperature.
It was devised in 1804 by John Leslie (1766–1832), a Scottish mathematician and physicist. [1] In the version of the experiment described by John Tyndall in the late 1800s, [2] one of the cube's vertical sides is coated with a layer of gold, another with a layer of silver, a third with a layer of copper, while the fourth side is coated with a varnish of isinglass. The cube is made from a solid block of metal with a central cavity. In use, the cavity was filled with hot water; the entire cube has essentially the same temperature as the water. The thermal detector (on the far right in the figure) showed much greater emission from the side with varnish than from any of the other three sides.
In contemporary terms, the emissivities of shiny metals are low. Isinglass is an organic glue, and has a much larger emissivity than the metals. Leslie's cube is still in use to demonstrate and measure the variations in emissivities for different materials. [3] In the figure, the false color images ("thermographs") of a cube at about 55 °C were taken with an infrared camera; the black and white photographs are taken with an ordinary camera. The black face of the cube is highly emissive, as indicated by the reddish color of the thermograph. The mirror-like, polished face of the aluminum cube emits thermal radiation weakly, as indicated by the blue color. The reflection of the experimenter's hand is green, which corresponds to a high emissivity surface near body temperature (37 °C). The photographs also show that the white painted surface is nearly as emissive as a black surface.
A modern version of Leslie's Cube is part of the structure of a small earth-orbiting satellite known as FUNcube-1 and registered as a Dutch spacecraft. Launched in November 2013, it demonstrates the absorption and emission of solar radiation in space as the satellite orbits in full sunlight, eclipse and rotates around its three axes. [4]
The Crookes radiometer consists of an airtight glass bulb containing a partial vacuum, with a set of vanes which are mounted on a spindle inside. The vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity.
The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere.
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from the nominal red edge of the visible spectrum around 700 nanometers, to 1 millimeter (300 GHz). Black-body radiation from objects near room temperature is almost all at infrared wavelengths. As a form of electromagnetic radiation, IR propagates energy and momentum, with properties corresponding to both those of a wave and of a particle, the photon.
A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body also emits black-body radiation. In contrast, a white body is one with a "rough surface that reflects all incident rays completely and uniformly in all directions."
The Stefan–Boltzmann law describes the power radiated from a black body in terms of its temperature. Specifically, the Stefan–Boltzmann law states that the total energy radiated per unit surface area of a black body across all wavelengths per unit time is directly proportional to the fourth power of the black body's thermodynamic temperature T:
A pyrometer is a type of remote-sensing thermometer used to measure the temperature of distant objects. Various forms of pyrometers have historically existed. In the modern usage, it is a device that from a distance determines the temperature of a surface from the amount of the thermal radiation it emits, a process known as pyrometry and sometimes radiometry.
Radiative cooling is the process by which a body loses heat by thermal radiation. As Planck's law describes, every physical body spontaneously and continuously emits electromagnetic radiation.
Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material is converted to electromagnetic radiation. All matter with a temperature greater than absolute zero emits thermal radiation. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation.
Incandescence is the emission of electromagnetic radiation from a hot body as a result of its high temperature. The term derives from the Latin verb incandescere, to glow white. A common use of incandescence is the incandescent light bulb, now being phased out.
Infrared thermography (IRT), thermal video and thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are examples of infrared imaging science. Thermographic cameras usually detect radiation in the long-infrared range of the electromagnetic spectrum and produce images of that radiation, called thermograms. Since infrared radiation is emitted by all objects with a temperature above absolute zero according to the black body radiation law, thermography makes it possible to see one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature; therefore, thermography allows one to see variations in temperature. When viewed through a thermal imaging camera, warm objects stand out well against cooler backgrounds; humans and other warm-blooded animals become easily visible against the environment, day or night. As a result, thermography is particularly useful to the military and other users of surveillance cameras.
Black-body radiation is the thermal electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, emitted by a black body. It has a specific spectrum of wavelengths, inversely related to intensity that depend only on the body's temperature, which is assumed for the sake of calculations and theory to be uniform and constant.
A radiant barrier is a type of building material that reflects thermal radiation and reduces heat transfer. Because thermal energy is also transferred by conduction and convection, in addition radiation, radiant barriers are often supplemented with thermal insulation that slows down heat transfer by conduction or convection.
In solar thermal collectors, a selective surface or selective absorber is a means of increasing its operation temperature and/or efficiency. The selectivity is defined as the ratio of solar radiation absorption (αsol) to thermal infrared radiation emission (εtherm).
The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that may include both visible radiation (light) and infrared radiation, which is not visible to human eyes. The thermal radiation from very hot objects is easily visible to the eye. Quantitatively, emissivity is the ratio of the thermal radiation from a surface to the radiation from an ideal black surface at the same temperature as given by the Stefan–Boltzmann law. The ratio varies from 0 to 1. The surface of a perfect black body emits thermal radiation at the rate of approximately 448 watts per square metre at room temperature ; all real objects have emissivities less than 1.0, and emit radiation at correspondingly lower rates.
Low emissivity refers to a surface condition that emits low levels of radiant thermal (heat) energy. All materials absorb, reflect, and emit radiant energy according to Planck's law but here, the primary concern is a special wavelength interval of radiant energy, namely thermal radiation of materials. In common use, especially building applications, the temperature range of approximately -40 to +80 degrees Celsius is the focus, but in aerospace and industrial process engineering, much broader ranges are of practical concern.
Calorescence is a term describing the process whereby matter absorbs infrared radiant energy and emits visible radiant energy in its place. For example, some kinds of flammable gas give off large amounts of radiant heat and very little visible light when burning, and if a piece of metal is placed into such a flame, the metal will become bright red-hot—which is to say the metal absorbs invisible infrared and emits visible radiation. The word calorescence was coined by John Tyndall in 1864 on the model of the word fluorescence which had been coined in 1852. At that time, fluorescence was defined as absorption in the ultraviolet part of the spectrum followed by emission in the visible part of the spectrum. Calorescence was defined complementarily as absorption in the infrared followed by emission in the visible. Earlier, George Stokes had shown the reverse phenomenon: the emission of infrared following the absorption of visible light.
Multi-layer insulation (MLI) is thermal insulation composed of multiple layers of thin sheets and is often used on spacecraft and Cryogenics. Also referred to as superinsulation, MLI is one of the main items of the spacecraft thermal design, primarily intended to reduce heat loss by thermal radiation. In its basic form, it does not appreciably insulate against other thermal losses such as heat conduction or convection. It is therefore commonly used on satellites and other applications in vacuum where conduction and convection are much less significant and radiation dominates. MLI gives many satellites and other space probes the appearance of being covered with gold foil which is the effect of the amber-coloured Kapton layer deposited over the silver Aluminized mylar.
An infrared heater or heat lamp is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the emitting body, the wavelength of the peak of the infrared radiation ranges from 780 nm to 1 mm. No contact or medium between the two bodies is needed for the energy transfer. Infrared heaters can be operated in vacuum or atmosphere.
Radiant heating and cooling is a category of HVAC technologies that exchange heat by both convection and radiation with the environments they are designed to heat or cool. There are many subcategories of radiant heating and cooling, including: "radiant ceiling panels", "embedded surface systems", "thermally active building systems", and infrared heaters. According to some definitions, a technology is only included in this category if radiation comprises more than 50% of its heat exchange with the environment; therefore technologies such as radiators and chilled beams are usually not considered radiant heating or cooling. Within this category, it is practical to distinguish between high temperature radiant heating, and radiant heating or cooling with more moderate source temperatures. This article mainly addresses radiant heating and cooling with moderate source temperatures, used to heat or cool indoor environments. Moderate temperature radiant heating and cooling is usually composed of relatively large surfaces that are internally heated or cooled using hydronic or electrical sources. For high temperature indoor or outdoor radiant heating, see: Infrared heater. For snow melt applications see: Snowmelt system.
In light-emitting diode physics, the recombination of electrons and electron holes in a semiconductor produce light, a process called "electroluminescence". The wavelength of the light produced depends on the energy band gap of the semiconductors used. Since these materials have a high index of refraction, design features of the devices such as special optical coatings and die shape are required to efficiently emit light. An LED is a long-lived light source, but certain mechanisms can cause slow loss of efficiency of the device or sudden failure. The wavelength of the light emitted is a function of the band gap of the semiconductor material used; materials such as gallium arsenide, and others, with various trace doping elements, are used to produce different colors of light. Another type of LED uses a quantum dot which can have its properties and wavelength adjusted by its size. Light-emitting diodes are widely used in indicator and display functions, and white LEDs are displacing other technologies for general illumination purposes.
draper, john william.In 1856, Draper described the device as a cubical brass vessel set upon a vertical rotatable stem. At a little distance is the blackened bulb of a differential thermometer. A mirror reflects the infrared rays of the cube onto the bulb. One of the sides of the cube is left with a clear surface, another with a coat of varnish, the third with two, and the fourth with three coats. It was found that more heat escaped as the number of coats increased. In the experiments of Macedonio Melloni, it was found that the maximum rate of radiation was at 16 coats.
John Leslie.
john leslie mathematics.
leslie cube.