√ Definition of Black Body Radiation, Heat Radiation, Formulas & Example Problems
Definition of Black Body Radiation, Heat Radiation, Formulas & Example Problems – In this discussion we will explain about black body radiation. Which includes the notion of black body radiation, heat radiation, formulas and examples of black body radiation problems which are discussed in full and lightly. For more details, please see the review below carefully.
Definition of Black Body Radiation, Heat Radiation, Formulas & Example Problems
Let's discuss the meaning of black body radiation first carefully.
Definition of Black Body Radiation
Black is a color that absorbs all light or rays that fall on it, causing the object to heat up. An example is when you wear black clothes or shirts during the day, of course it is very hot. This event is called black body radiation.
Black body radiation is a type of thermal electromagnetic radiation that occurs around or within objects in a state of thermodynamic equilibrium with its environment or when there is a process of discharge from the body black. Meanwhile, a black body is an object that is opaque and cannot reflect light.
If we look in detail at an incandescent lamp, the filament on the lamp has a whitish yellow color even though the lamp is blue. This happens because the incandescent lamp has a temperature above 2000 K. All objects that have an angle above 2,000 K will emit white light.
Light propagates through a vacuum, light is considered a wave, almost the same as interference and diffraction. Which in the event of the interaction of light with atoms or molecules, light is considered as a particle. These events include heat radiation, photoelectric effect, and Compton's phenomenon.
Definition of Heat Radiation
Heat radiation or also called heat radiation is radiation emitted from an object as a result of its temperature. Each object emits heat radiation, but generally, we can see an object because the object reflects the light incident on it, not because the object emits radiation hot.
The object will be visible because it radiates heat when the temperature is over 1,000 K. At this temperature objects begin to glow red, such as the heating coil of an electric stove. At temperatures above 2,000 K the glowing object becomes whitish or yellow, like the white glow of an incandescent lamp filament.
If the temperature of the object is increased, the relative intensity of the emitted light spectrum changes. This causes a shift in the colors of the observed spectrum, which can be used in determining the temperature of an object.
In general, the detailed shape of the spectrum of heat radiation emitted from a hot body depends on the composition of the object. Even so, the experimental results state that there is one class of hot objects that emit hot spectra with universal characteristics. This object is a black body or black body.
As explained earlier, that a black body absorbs all incoming radiation. Another term is that no radiation is reflected out of a black body. So a black body has an absorbance and emissivity values equal to one.
Emissivity (emitting power) is a characteristic of a material, which describes the ratio of emitted power per unit area of a surface to the power emitted by a black body with the same temperature. Whereas absorption (Absorptive power) is the ratio of the flux of light emitted or absorbed from an object to the flux that comes from that object.
A black body is likened to a black cavity with a small hole. Very little light enters the cavity through the hole, the light beam will be reflected repeatedly inside the cavity without being able to come out again from the hole.
Every time it is reflected, the light will be absorbed by the black walls. A black body will absorb the light around it if the temperature is lower than the surrounding temperature and will emit light to the surroundings if the temperature is higher than the surrounding temperature. This can be seen in the image below, if a black object is heated to a high enough temperature it will look smoldering.
A perfect black body is a good emitter of heat (e = 1). An almost perfect example is a hermetically sealed box perforated with air inlets (vents) in the house.
Black Body Radiation Formula
Black body radiation spans all wavelengths. The energy distribution in this wavelength region has a special feature, namely a maximum value at a certain wavelength. The location of the maximum value depends on the temperature, which will move or shift towards the short wavelength direction as the temperature increases.
In 1879 the Austrian physicist named Josef Stefan carried out an experiment to find out the universal character of black body radiation. Later he found that the total power per unit area radiated at all frequencies from a hot black body (total intensity) is proportional to the fourth power of temperature absolutely. So it can be formulated:
I total = σ. T4 ………………………………………………. (1)
I shows that the intensity of radiation on the surface of the black body at all frequencies. T is the absolute temperature of the object and σ is the Stefan-Boltzman constant which is 5.67 x 10-8 Wm-2K-4
In the event of a hot body that is not a black body, it will fulfill a similar law, only given an additional emissivity coefficient which is smaller than 1 so that it becomes:
I total = e.σ.T4………………….. (2)
Intensity is power per unit area, so equation (2) can be written as:
P/A = e.σ.T4………………………..(3)
Under the condition:
P = radiation power (W)
A = Surface area of the object (m2)
e = emissivity coefficient
T = absolute temperature (K)
Several years later, on the basis of the theory of electromagnetic waves of light, Ludwih Boltzmann (1844 - 1906) theoretical inheritance of the laws expressed by Joseph Stefan (1853 – 1893) from the combined thermodynamics and equations Maxwell. Therefore, equation (2) is also known as the Stefan-Boltzmann Law, which reads:
"The amount of energy emitted per unit surface of a black body in unit time will be directly proportional to the fourth power of its thermodynamic temperature."
Examples of Black Body Radiation Problems
1.An incandescent lamp can be thought of as a sphere. The radius of the first incandescent lamp is 3 times the radius of the second incandescent lamp, the temperature of the first incandescent lamp is 67 oC and the temperature of the second is 407 oC. Then determine the ratio of the radiation power of the first incandescent lamp to the second incandescent lamp!
Is known:
T1 = (67 + 273)K = 340 K
T2 = (407 = 273)K = 680 K
R1 = 3 R2
Comparison of the radiation power of the (first) lamp to the second lamp.
Thus has been explained about Definition of Black Body Radiation, Heat Radiation, Formulas & Example Problems, hopefully can add to your insight and knowledge. Thank you for visiting and don't forget to read other articles.
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