Black Body
In physics, a black body (United Kingdom black body) is an object that absorbsthe entire electromagnetic radiation that falls on him. Before continuing yourreading activities, help us to click the image on the side. There is no radiationcan exit or looking. However, in classical physics, theoretical black body mustalso emit a whole wavelength energy is possible, because it is only from thisenergy that objects can be measured.

Although his name is black body, he does not have to actually black because she was also emits energy. The number and type of electromagnetic radiationthat dipancarkannya depends on the temperature of the black body. Black bodywith a temperature below approx. 700 Kelvin almost all its energy emitted in the form of infrared waves, very little in the visible wavelengths. The higher thetemperature, the more energy is emitted in the visible wavelengths starts fromred, Orange, yellow and white.

The term "black body" was first introduced by Gustav Kirchhoff in 1862. The light emitted by a black body radiation blackbody is referred

In the laboratory, the most objects approaching the black body radiation isradiation from a small hole in a cavity. Any light entering the hole this will bereflected and its energy is absorbed by the walls of the cavity multiple times, without being concerned about your wall material and the wavelength ofincoming radiation (as long as the wavelengths smaller than the diameter of thehole). This hole (not the sockets) is the approach of a black body. If the cavity is heated, the spectrum emitted from the hole will be a continuous spectrum andis not dependent on the manufacturer of the cavity. A steady stream ofradiasinya following a general curve (see figure). Based on Kirchhoff's law of thermal radiation of this curve depends only on the temperature of the walls ofthe cavity, and every black body will follow this curve.

The observed spectrum can not be explained by classical electromagnetic theoryand statistical mechanics. This theory predicts high intensitasi at low wavelength(i.e., high frequency); a prophecy known as the ultraviolet catastrophe.

The theoretical problem is solved by Max Planck, who consider thatelectromagnetic radiation can propagate only in packets, or quanta (seeultraviolet catastrophe for details). This idea was later used by Einstein to explain the photoelectric effect. This theoretical developments eventually led to the classical electromagnetic theory replaces with quantum mechanics. Currently,these packets are called photons.
There are objects that are easy to absorb radiation, there is also an easily emitradiation and vice versa. Objects that can absorb the whole radiation that he received and emits radiation throughout the issue are known as black body.Black body is modeled as a cavity with a slit aperture is very small. If there areincoming radiation into the cavity through holes, the radiation will be reflectedover and over by the wall in the cavity so that the absorbed energy is exhausted.

There is no radiation reflected radiates out of the hole because the hole is very small. So, these little hollow cavity behaves as a blackbody radiation can absorbthe whole because he received. Similarly, if the cavity is emitting radiation, noradiation back into the cavity. Thus, the cavity will also radiate the whole energyissue. In physics, a black body (United Kingdom black body) is an object that absorbs radiation falling all over him. There is no radiation can exit or looking.However, in classical physics, theoretical black body must also emit a wholewavelength energy is possible, because it is only from this energy that objectscan be measured. Although his name is black body, he does not have to actuallyblack because she was also emits energy. 

The number and type of radiation thatdipancarkannya depends on the temperature of the black body. Black body with a temperature below approx. 700 Kelvin almost all its energy emitted in the form of infrared waves, very little in the visible wavelengths. The higher thetemperature, the more energy is emitted in the visible wavelengths starts fromred, Orange, yellow and white. The term "black body" was first introduced byGustav Kirchhoff in 1862. 

The light emitted by a black body radiation blackbody is referred to. Black bodysurface is a surface that has the properties as a transmitter or a very goodradiation absorber. If the surface temperature is higher than the surrounding environment, it will be emitting radiation. However, if the temperature is low, it will be absorbing radiation.
Black body is a system that can absorb all the heat radiation on the object. But actually in this life there is no perfect black body, such as the definition above.However, black body can be assumed as a small hole in the hollow objects.

Stefan-Boltzman Law
In the year 1879 physicist from Austria, Josef Stefan experiment to know theuniversal character of black body radiation. He found that the total poweremitted per unit area on all frequencies by a hot black body (total intensity) isproportional to the absolute temperature of four ranks. So it can be formulated:
E I = σ T4
I expressed the intensity of radiation on the surface of a black body at all frequency, T is the absolute temperature of the body, and σ is the Stefan-Boltzman constant, which is worth 5.67 × 10-8 Wm-2 k-4. The following imageshows the spectrum of light emitted from perfect blackbody at several differenttemperatures. The graph shows that between between wavelengths radiated byan object's temperature has a very complicated relationship.
In the case of an object that is not a hot black body, will meet the same legal, just given the additional coefficient emissivity smaller than 

1 so that:
I total = e. σ. T ^ 4
Intensity is the power per unit area, then the above equation can be written as:
P = power (W) radiation
Q = heat energy (J)
A = surface area (m2)
e = emissivity coefficient
T = absolute temperature (K)

A few years later, based on the theory of electromagnetic waves light, LudwigBoltzmann (1844 – 1906) theoretically lower the law expressed by the JosephStefan (1853 – 1893) of the thermodynamic and Maxwell's equations. Therefore,the above equation is also known as the law of Stefan-Boltzmann, which reads:
"The amount of energy radiated per unit surface of a black body in unit time isdirectly proportional to the cube of the four temperature termodinamikanya".

2. Formulation of Rayleigh and Jeans
The curves obtained from previous experiments is an empirical result, i.e.obtained and it was concluded as a result of observations or experiments. At that time the scientists tried to find explanation for the empirical reality. At the time of the two scientists, namely Lord Rayleigh (1842-1919) and Sir JamesHopward Jeans (1877-1946) try using the kinetic theory of gases in classical physics to manipulate the results of the empirical.

According to classical physics on ekuipartisi energy, the average energy perdegree of freedom at a temperature T is ½ kT. Then the total energy for everyvibe wave be kT, k is defined by Stefan-Boltzmann.

Although it is impossible to be able to calculate the magnitude of the velocity ofeach particle in a gas chamber, maxwell's theory of velocity of each particle can associate these against the number of particles in a box and elaborated throughthe distribution curve of Maxwell. Here the Rayleigh-Jeans look at that curve that spelled out by maxwell is similar to the results obtained on the intensity ofthe heat radiation spectrum due to the spread of kinetic energy represented bythe spread of speed due to the kinetic energy can be expressed in speed. They therefore assumed that there are similarities between the nature of hot objects and heat radiation.

A little radiation is in the ultraviolet wavelength region. l run low. Deviationequation of Rayleigh-Jeans very much this next term katastropi ultravioletbecause l approaches zero. This highly empirical results that deviate from theshow that the intensity would be close to zero if the waning intensity, l will beenlarged. Even the intensity will go to Infinity if l is great. But the mathematicalresults obtained them for l approaches infinity then the intensity will be close tozero. This corresponds to the empirical results for l that enlarges, the intensitywill be getting smaller and if lBerdasarkan persaman ekuipartisi energy principle,mathematically derived by Rayleigh and Jeans.

It is because they think that the energy possessed by any spectral bands arekotinu. That is, the wave energy can have any value within the limits specified.So the energy values obtained may be infinite numbers. And these assumptionsyield a function which resulted in discrepancies with the results of experimentson the short wavelength.

The legal shift in wien
When the temperature of the object is constantly improved, relative to the intensity of the emitted light spectrum changes. This caused a shift in coloursspectrum is observed, which can be used to estimate the temperature of an object as in the picture:

Graph Shifting Wien

The image above shows the graph between the intensity of radiation emitted bya black body against wavelength (graph I – l) at different temperatures. Total energy heat radiation emitted is proportional to the size at bawag graphs. It appears that the total heat energy radiation radiation increases with increasingtemperature (according to inform Stefan-Bolztman. Heat energy is proportional to the absolute temperature of four ranks.

Heat radiation appear comparable suatau spectra is continuous, not discretespectra such as streaks of light seen in the spectra of fire. Or dark streaks can be seen in the light of the Sun (Fraunhofer lines) (Spectra is the singular spectrum) instead, all the wavelength distribution of the heat energy present in this vast. If the temperature increases, the bendahitam wavelength for maximum intensity(lm) shifted to shorter wavelengths
The measurement of black body spectra show that ran from wavelengthmaximum intensity (lm) decreases with increasing temperature, as shown in thefollowing equation:

λm = wavelengths with the maximum intensity (m)
T = the absolute temperature of the black body (K)
C = constant shifting Wien = 2.90 x 10-3 m K
At higher temperatures (in respect of the order of 1000 K) object starts flashingred, as iron is heated. At temperatures above 2000 K yellow or incandescentobjects keputih-putihhan, such as iron or white flashing incandescent filamentof incandescent white.

If a solid object is heated then it would radiate heat radiation. At normal temperature, we are not aware of this electromagnetic radiation due to lowintensitasnya. At higher temperatures there is enough infrared radiation that we can not see but we can feel the heat if we are closer to the object.

The Theory Of Max Planck
Failure theory of Rayleigh-Jeans pushing a German physicist Max Planck (1858-1947) to try another approach.

Planck realized the importance of to include the concept of maximum energy in the calculation of the theoretical black body radiation. According to Planck, the energy absorbed or emitted by the vibrations arising within the black bodycavity is the packets or quanta. The magnitude of the energy of each package is a multiple of the original number of hf with h is Planck constant magnitude 6.63 ¬ ¬ ¬ x 10-34 Js and f is the frequency of the energy package. Mathematically,Planck's formulation can be written into
E = nhf
where n is a multiple of the natural numbers.

Planck made the rule that every energy vibrating mode should not be more thanthe average energy owned radiation (kT). However, because the energy of the vibrating mode may be dimilki by the nhf, meaning the higher the frequency,the less likely not to exceed kT.

Planck's quantum relationship suggests that ekuipartisi energy and any kind ofvibration has a total energy. According to Planck, classical theory failed toexplain blackbody radiation at shorter wavelengths because in that area quantaenergy so great that only a few types of vibration. The reduced type vibrationexcited vibration resulting in depressed and radiation will decrease towards zeroat high frequencies. Hence Planck's formula can be spared from ultravioletcatastropi.

The equation shows the magnitude of the energy per unit area emitted by ablack body that was distributed among the various length has been lowered by Max Planck in 1900 by using quantum theory, i.e. as follows,

E = (2πc ^ 2 h)/λ ^ 2 [1/(e ^ (hc/λkT)-1)]
In the equation, c is the speed of light, your vines are the wavelength λ and T isthe absolute temperature of the surface of the black body. The constant k and hare calculated based on experimental data, i.e. the klPada equation, c is the speed of light, the vines

k = 1.38 x 10-11 JK-1 ¬ (called the Boltzmann constant)
h = 6.63 x 10-34 Js (called Planck's constant)
Max T = 3 x 10-2.898 ¬ ¬ mK. lmaks) and the absolute temperature (T) of a black body has been lowered by Wien shift law known as wien, yaknilHubungan between the wavelength of maximum energy.

According to Planck, atoms in cavity wall black objects have properties such asharmonic oscillator. The energy possessed by the harmonic oscillator-oscillatoronly at certain values of f. Values are multiples of the original number of hf, namely hf, 2hf, 3hf, and so on. The harmonic oscillator may not have energy in addition to the prices. By Planck's oscillator energies that are said to bequantized.

Application Of Black Body Radiation
Home KacaSalah GlobalEfek Warming symptoms one cause of global warming is the increase in greenhouse gases (greenhouse effect). The greenhouse effect the Earth's temperatures have increased an average of 1 to 5 degrees Celcius. simple Analogy to describe the greenhouse effect is when we Park the car in the parking lot are open during the day. When we returned to the car in the afternoon, usually the temperature in the car is hotter in the compare the temperature outside. Since most of heat energy from the Sun has been in absorbency by the seats, dashboard and car carpets. When the objects heat energy, not everything can get out through the window but some pantulkan back. The reason is the difference in the wavelengths of sunlight that enters the car and heat energy is released again by the Chair. So the amount of energy that goes more than energy out. As a result of gradual increase in temperature inside the car. If there were no atmosphere, the energy of the Sun to the Earth will be able to heat the Earth until it reaches a temperature of 800C in the region of the equator. Fortunately, the layer of the Earth's atmosphere is capable of reflecting about 34% of the energy of the Sun to the earth so that a return to outer space. About 19% absorbed by the clouds and dust in the atmosphere and about 47% of its total energy reaching the Earth's surface. The earth does not get warm up evenly. Near the equator, the Earth absorbs radiation heat greater than near the polar regions. Thanks to the flow pattern heat energy is absorbed. The earth does not become too hot.

47% of the energy from solar radiation absorbed by the Earth's surface,approximately 23% is used to vaporize the water on the surface of the Earth.About 10% return in the form of keangkasa streamed of conduction and convection and about 14% of the wave in the form of elektromgnetik emittedinto space. The sunlight that enters the Earth's surface has a wide range ofwavelengths. The rays seemed to be on a wavelength between 400-700 nm,infrared light at wavelengths above 700 nm and ultraviolet light at wavelengthsbelow 400 nm.

Sun with short wavelengths, such as ultraviolet light and x-rays, can easilypenetrate the layers of Earth's atmosphere. When this solar energy heats theEarth, most of the energy emitted by the Earth into space as a wave length. The energy absorbed is reflected back in the form of infrared radiation by clouds and the Earth's surface. But the majority of the emitted infrared Earth held up bya cloud of gas and CO2 and other gases, to be returned to the Earth's surface. In fact under normal circumstances, the greenhouse effect is required, to maintain the heat on Earth. In the absence of the greenhouse effect, the Earth's conditionwill probably like Mars, where there is very cold conditions and does not allowthe existence of life.

The result of the behavior of humans causing a rise in the concentration ofcarbon dioxide (CO2) and other gases in the atmosphere. The increase in the concentration of CO2 increase is due to the burning of fuel oil (FUEL), coal andother organic fuel that exceeded the ability of the plants and the sea tomengabsorbsinya.

Temperature measuring MatahariPada temperature high enough, naturally instars, fusion reactions will occur i.e. light nuclei join to form heavier nuclei.Through a series of stages of the fusion reaction, hydrogen nuclei join to formhelium nuclei. The process of merging it used to generate energy in stars.

The energy produced by the Sun or the stars of comprising various forms ofelectromagnetic radiation that can be known through the frequency orwavelength. All electromagnetic waves that dpancarkan will propagate in spacewith the same speed, the speed of the light spectrum By examining the spectrum of a star, an astronomer will be able to know the temperature of the star. No closer to the Sun or a star with guided radiation spectrum of black body. During the day, we will feel more comfortable wearing white rather thanblack-colored shirt. However, at night the cold we'll feel warmer when wearing ablack shirt instead of a white shirt. It shows that a dark surface is absorbent anda good heat and transmitter surfaces white or shiny is absorbent and heattransmitters.

The working principle of the flask as follows: shiny silver lining to prevent heattransfer in radiation. The coating reflects the Sun's radiation back into the flask.Walls of glass, as a conductor, can not move the kalorRuang vacuum between two walls to prevent the transfer of heat, either by convection or conduction.The stopper is made from insulators. This is done with the intent to preventconvection with outside air occurs. In hot weather, our skin sweating. This sweatevaporates and kalornya taken from our own body so that our bodies become more cool. 

Unlike humans, dogs do not have sweaty skin. When the weather ishot, the dog poked his tongue in the evaporation of water on his saliva, and the body of a dog becoming more cold water dinginMengapa in the jar (made of clay) cooler than the water that is stored in a plastic vessel? On the wall of the jar there are pores (cracks). The heat required for the vaporization of water was taken from the jug and the water inside. This causes the water in a pitcher orcooler because it cannot be that heat out the jar.

SuryaPanel solar panel is a device used to absorb radiation from the Sun. Solar panel consists of a hollow metal container at the black cat with the front panel is made of glass. Heat radiation from the Sun is absorbed by the surface of theblack and generally consigned to the conduction through metal. The inside ofthe panel is kept warm by the greenhouse effect, then the circulation of water through the metal containers will carry heat away to be utilized on the systempamanas the domestic water and cooled for a swimming pool.

Postingan terkait:

Belum ada tanggapan untuk "BLACK BODY RADIATION"

Post a Comment