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amukher
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The energy emitted by a body in watts/m2 is = εσT4. In the case of a perfect black body, ε=1. If the body only emits IR light, what should be the value of ε?
If the "body" is a light source not due to thermal radiation, then there is no ε. A CO2 laser will not emit the same power as a remote control, even if they are at the same temperature.amukher said:If the body only emits IR light, what should be the value of ε?
The emissivity is material dependent and surface roughness dependent. For example polished metal and foil of the same metal will have different emissivities, as shown here.amukher said:The energy emitted by a body in watts/m2 is = εσT4. In the case of a perfect black body, ε=1. If the body only emits IR light, what should be the value of ε?
amukher said:If the body only emits IR light, what should be the value of ε?
DrClaude said:If the "body" is a light source not due to thermal radiation, then there is no ε. A CO2 laser will not emit the same power as a remote control, even if they are at the same temperature.
The emissivity depends on the body shape (e.g how smooth it is) and the material. There's no easy way to predict them, they are basically empirical valuesamukher said:Let us say that the atmosphere blocks all visible light wavelengths and allows only IR wavelengths to reach the earth. The Earth would then be a source of thermal radiation. To calculate the heat emitted by the earth, I would need the value of ε.
To calculate the energy emitted through IR waves, you will need to use the Stefan-Boltzmann law. This law states that the energy (E) emitted per unit time (t) from a black body is proportional to the fourth power of its absolute temperature (T) and its surface area (A). The equation is written as E = σAT^4, where σ is the Stefan-Boltzmann constant (5.67 x 10^-8 W/m^2K^4).
A black body is an idealized object that absorbs all radiation incident on its surface and emits radiation at the maximum possible rate at any given temperature and wavelength. In other words, it is a perfect absorber and emitter of radiation. This concept is important in calculating energy emitted through IR waves because it allows us to use the Stefan-Boltzmann law, which is based on black body radiation.
Yes, the energy emitted through IR waves can also be calculated for non-black body objects. However, in this case, we need to use a modification of the Stefan-Boltzmann law called the emissivity (ε). Emissivity is a measure of how well an object emits IR radiation compared to a perfect black body at the same temperature. The equation for calculating energy emitted from a non-black body object is E = εσAT^4.
The temperature of an object has a direct effect on the amount of energy emitted through IR waves. As the temperature increases, the energy emitted also increases according to the Stefan-Boltzmann law. This means that hotter objects will emit more energy through IR waves compared to cooler objects.
Yes, it is possible to measure the energy emitted through IR waves using a device called an infrared (IR) thermometer. This device uses a lens to focus IR energy from an object onto a detector, which then converts the energy into an electrical signal. The signal is then displayed on a screen as a temperature reading. However, it is important to note that IR thermometers can only measure the surface temperature of an object, not the internal temperature.