Mention any three properties of thermal radiation

Observe how radiation from atomic bombs and nuclear disasters remains a major environmental concern Radiation may be thought of as energy in 10 centimetres (186,000 miles) per second—or at speeds less than that of light but appreciably greater than thermal velocities (e.g., the velocities of molecules forming a sample of air). The first type At one time, electromagnetic rays were thought to be inherently wavelike in character—namely, that they spread out in space and are able to exhibit Electromagnetic rays and neutrinos Visible light and the other components of the electromagnetic spectrum According to the theory of

This chapter describes the basic theory of thermal radiation and electrodynamics, as well as the definition and prediction of optical and radiative properties of solid materials. This chapter describes the thermodynamics foundation of the Stefan-Boltzmann law and the Planck law of blackbody radiation. Definitions of the radiative properties and their relationships are then presented, for example, emissivity, absorptivity, and reflectivity for opaque materials, as well as the reflectance, transmittance, and absorptance for semitransparent materials. Brief discussions on effective emissivity and radiative transfer in participating media are also presented. Maxwell's electromagnetic wave theory is introduced for the prediction of reflection and transmission at the interfaces as well as in multilayer structures. Frequency-dependent dielectric function models are described for metals, dielectric materials or insulators, and semiconductors, in the visible (VIS) and infrared (IR) regions. In 1900, Planck introduced the concept of energy quanta in order to derive the law of thermal radiation. In 1905, Einstein used the concept of energy quantization to explain the phenomenon of photoelectric emission. Later in 1924, de Broglie hypothesized that a physical particle could also exhibit wave nature. Wave-particle duality became an established foundation of quantum mechanics and more broadly modern physics. According to this theory, radiation is made of discrete energy quanta, called p...

1)Thermal radiation emitted by a body at any temperature consists of a wide range of frequencies. The frequency distribution is given by Planck's law of black-body radiation for an idealized emitter. 2)The dominant frequency (or color) range of the emitted radiation shifts to higher frequencies as the temperature of the emitter increases. For example, a red hot object radiates mainly in the long wavelengths (red and orange) of the visible band. If it is heated further, it also begins to emit discernible amounts of green and blue light, and the spread of frequencies in the entire visible range cause it to appear white to the human eye; it is white hot. However, even at a white-hot temperature of 2000 K, 99% of the energy of the radiation is still in the infrared. This is determined by Wien's displacement law. In the diagram the peak value for each curve moves to the left as the temperature increases. 3)The total amount of radiation of all frequencies increases steeply as the temperature rises; it grows as T4, where T is the absolute temperature of the body. An object at the temperature of a kitchen oven, about twice the room temperature on the absolute temperature scale (600 K vs. 300 K) radiates 16 times as much power per unit area. An object at the temperature of the filament in an incandescent light bulb--roughly 3000 K, or 10 times room temperatureradiates 10,000 times as much energy per unit area. The total radiative intensity of a black body rises as the fourth power ...

Thermal radiation is one of the three basic forms of heat transfer (conduction, convection, and radiation), being a basic property of matter depending on its temperature. In microcosmic point of view, thermal radiation is the result of random particle motion (due to the material temperature) resulting in charge acceleration or dipole oscillation of the electrons and protons. In contrast to conduction and convection, thermal radiation has two unique properties: (1) it does not require a medium to be transferred but being electromagnetic energy can interact with intervening materials; and (2) during the emission/absorption of radiation, there is transfer between electromagnetic energy and kinetic energy of atoms, namely, thermal energy. These two properties result... • Bergman TL, Incropera FP, DeWitt DP, Lavine AS (2011) Fundamentals of heat and mass transfer. Hoboken, New Jersey, Wiley • Cohen JD, Butler BW (1998) Modeling potential structure ignitions from flame radiation exposure with implications for wildland/urban interface fire management. In: Proceedings of the 13th fire and forest meteorology conference, International Association of Wildland Fire. pp 81–86 • Finney MA, Cohen JD, McAllister SS, Jolly WM (2013) On the need for a theory of wildland fire spread. Int J Wildland Fire 22(1):25–36 • Frankman DJ (2009) Radiation and convection heat transfer in wildland fire environments[D], PhD Thesis, Brigham Young University • Hankinson G, Lowesmith BJ (2012) A considerati...

1)Thermal radiation emitted by a body at any temperature consists of a wide range of frequencies. The frequency distribution is given by Planck's law of black-body radiation for an idealized emitter. 2)The dominant frequency (or color) range of the emitted radiation shifts to higher frequencies as the temperature of the emitter increases. For example, a red hot object radiates mainly in the long wavelengths (red and orange) of the visible band. If it is heated further, it also begins to emit discernible amounts of green and blue light, and the spread of frequencies in the entire visible range cause it to appear white to the human eye; it is white hot. However, even at a white-hot temperature of 2000 K, 99% of the energy of the radiation is still in the infrared. This is determined by Wien's displacement law. In the diagram the peak value for each curve moves to the left as the temperature increases. 3)The total amount of radiation of all frequencies increases steeply as the temperature rises; it grows as T4, where T is the absolute temperature of the body. An object at the temperature of a kitchen oven, about twice the room temperature on the absolute temperature scale (600 K vs. 300 K) radiates 16 times as much power per unit area. An object at the temperature of the filament in an incandescent light bulb--roughly 3000 K, or 10 times room temperature—radiates 10,000 times as much energy per unit area. The total radiative intensity of a black body rises as the fourth power...

Blackbody Radiation It is known that the amount of radiation energy emitted from a surface at a given wavelength depends on the material of the body and the condition of its surface as well as the surface temperature. Therefore, various materials emit different amounts of radiant energy even whhen they are at the same temperature. A body that emits the maximum amount of heat for its absolute temperature is called a blackbody. A blackbody is an idealized physical body, that has specific properties. By definition, a black body in thermal equilibrium has an emissivity of ε = 1.0. Real objects do not radiate as much heat as a perfect black body. They radiate less heat than a black body and therefore are called gray bodies. The surface of a blackbody emits thermal radiation at the rate of approximately 448 watts per square metre at room temperature (25 °C, 298.15 K). Real objects with emissivities less than 1.0 (e.g. copper wire) emit radiation at correspondingly lower rates (e.g. 448 x 0.03 = 13.4 W/m 2). Emissivity plays important role in heat transfer problems. For example, solar heat collectors incorporate selective surfaces that have very low emissivities. These collectors waste very little of the solar energy through emission of thermal radiation. Since the absorptivity and the emissivity are interconnected by the Kirchhoff’s Law of thermal radiation, a blackbody is also a perfect absorber of electromagnetic radiation. Kirchhoff’s Law of thermal radiation: For an arbitrar...

Properties of thermal radiation: 1. It travels through a vacuum with the velocity of light. 2. It travels in a straight line. 3. It undergoes reflection, refraction and total internal reflection. 4. It exhibits the phenomenon of interference, diffraction and polarisation. 5. Intensity of radiation decreases with increase in distance.