What material absorbs all radiation?
Light absorption is a process by which light is absorbed and converted into energy. An example of this process is photosynthesis in plants. However, light absorption doesn’t occur exclusively in plants, but in all creatures/inorganic substances. Absorption depends on the electromagnetic frequency of the light and object’s nature of atoms. The absorption of light is therefore directly proportional to the frequency. If they are complementary, light is absorbed. If they are not complementary, then the light passes through the object or gets reflected. These processes usually occur at the same time because the light is usually transmitted at various frequencies. (For instance, sunlight also comprises lights of various frequencies; from around 400 to 800 nm). Therefore, most objects selectively absorb, transmit, or reflect the light. When light is absorbed heat is generated. So the selective absorption of light by a particular material occurs because the frequency of the light wave matches the frequency at which electrons in the atoms of that material vibrate.
Absorption depends on the state of an object‘s electron. All electrons vibrate at a specific frequency, which is known as their «natural» frequency. When light interacts with an atom of the same frequency, the electrons of the atom become excited and start vibrating. During this vibration, the electrons of the atom interact with neighboring atoms and convert this vibrational energy into thermal energy. Consequently, the light energy is not to be seen again, that is why absorption differs from reflection and transmission. And since different atoms and molecules have different natural frequencies of vibration, they selectively absorb different frequencies of visible light.
- 1 Examples
- 2 Applications
- 3 Light absorption and colors
- 4 Links
- 4.1 Related articles
- 4.2 External links
- 4.3 Bibliography
Examples [ edit | edit source ]
As was mentioned above, everything is capable of absorbing light. For example, organic molecules are good at absorbing light. If an organic molecule has electrons that have a high natural frequency then they absorb the light which has a high frequency as well. The longer the conjugated system(conjugated system is a system of connected pi-orbitals with delocalized electrons), the longer the wavelength of the light absorbed.
Another example. Let’s imagine that we are walking around a park with a lot of grass and plenty of beautiful flowers. As you already know, all living things have their own color. We can infer from this that all living or inorganic things reflect, absorb, and transmit light at the same time. Every matter has its own specific frequency at which its electrons vibrate so if the frequencies are complementary then the light is absorbed but on the other hand, if the frequencies are not complimentary light is reflected or transmitted. Colors we can see around us are the result of transmission, absorption, and reflection of light caused by non-complementary frequencies.
Applications [ edit | edit source ]
By relying on this method, physicists are able to determine and identify the properties and material composition of an object by observing which frequencies of light it absorbs. While some materials are opaque to some wavelengths of light, they are transparent to others. Wood, for example, is opaque to all forms of visible light. Glass and water on the other hand are opaque to ultraviolet light, but transparent to visible light.
Light absorption and colors [ edit | edit source ]
Absorption of electromagnetic radiation requires an opposite-field i.e. the field which has the opposite coefficient in the same mode. A good example of this is color. If a material or matter absorbs light of certain wavelengths (or colors) of the spectrum, an observer will not see these colors in the reflected light. On the other hand, if certain wavelengths of colors are reflected from the material, these are the colors that the observer will see. For example, leaves contain the pigment chlorophyll, which absorbs the blue and red colors of the spectrum and reflects green therefore leaves appear green. To the naked eye, reflected light often appears to be refracted into several colors of the spectrum. As a result, light absorption is related to matter’s frequency (and frequency of light also) and wavelength of light.
Within the one-electron approximation, this is described by the promotion of an electron from a filled orbital to an unfilled orbital (in the case of diamagnetic materials). The difference in energy between those levels, (the excited state and the ground state), gives the energy of the photons that can be absorbed.
Several parameters can be used to characterize this transition, including the energy of the incident radiation required for the efficient absorption of the light and the inherent ability of the molecules to absorb radiation of the appropriate energy by the Planck relation:
This graphic shows what color will be perceived when a material absorbs in certain regions of the visible spectrum.
If wavelengths of light from a certain region of the spectrum are absorbed by a material, then the materials will appear to be the complementary color Thus, for instance, if violet light with wavelength of 400nm is absorbed, the material will look yellow. If the material absorbs blue you will see the color orange.
Color absorbed Color seen Violet Yellow Blue Orange Green Red Yellow Violet Orange Blue
Note that green is not indicated in the figure; this is because materials that appear green actually absorb in the red and the blue (i.e., about 650 nm and 425 nm) band shape and color
Our ability to perceive very small differences in color is rather extraordinary; for instance, two solutions which appear to have virtually identical absorption spectra, with minute differences in their tails, can be recognized as clearly different hues. Very small changes in the shape of an absorption band (not only the position) will cause materials to appear different shades
Bright and Dull
A sharp absorption peak results in the perception of a saturated color.
In general, colors that we perceive as brilliant and bright have strong narrow absorption bands whereas dull colors tend to have weaker and broader absorption bands.
The hue is that aspect of color usually associated with terms such as red, orange, yellow, and so forth.Hue distinguishes the color purity of the dominant color (i.e. red from yellow). The position of absorption maxima largely determines this property.
saturation (also known as chroma, or tone) refers to relative purity; when a pure, vivid, strong shade of red is mixed with a variable amount of white, weaker or paler reds are produced, each having the same hue but a different saturation; such paler colors are called unsaturated colors. You can define the amount of saturation of a given using a chromaticity diagram. For example, suppose you had a red color and you slowly increased the amount of blue and green light reaching the eye, then the mixture of the red, blue and green would contribute to the perception of white. White plus red would give pink. The hue would not have been altered, but the saturation would be lower
Light of any given combination of hue and saturation can have a variable brightness (also called intensity, lightness, or value), which depends on the total amount of light energy present. Lightness of a color is changed by varying the intensity of all three primary colors by the same amount. For example, if the intensity of a red were increased it would appear brown.
All colors can be create by the addition of the primary colors. Use this Flash application to explore color mixing.
An In Depth Guide To Understanding Black Bodies
A black body, also written as blackbody, is a theoretical construct describing an object that absorbs all electromagnetic radiation falling onto it, leaving all wavelengths of light to be absorbed as well. In turn, no light is reflected. Without reflected light, the object will appear black, hence the name “blackbody.” Contrary to popular belief, this construct is currently impossible for man to create–it is considered theoretical. It is possible to create an object that is almost a blackbody, meaning the object captures most of the radiation falling onto it, but not all.
What Are The Characteristics of a Black Body?
Black bodies are characterized by their ability to absorb all radiation they come in contact with. There are specific factors that go into the allowance of this mass absorption. Foremost, the coefficient for absorption must be equal to one. If the absorption coefficient is one, then the coefficient of reflection, when combined with the coefficient of transmission, is equal to zero. In simpler, less technical terms, black bodies will not reflect or transmit light, only heat in proportion to their temperature. This proportionate heat emission is what ensures objects don’t reach an infinitely hot temperature.
Examples of a Black Body
While stars are not technically a perfect example of a blackbody, they come quite close. Any photon that reaches a star gets completely absorbed. Furthermore, stars mirror black bodies: they emit heat in proportion to their current temperature. That is why stars, similarly to black bodies, vary in color, as different stars remain at different temperatures. Red stars, for example, are cool and emit the majority of their radiation in red wavelengths. A warmer star, such as the sun, emits the most radiation in yellow and green wavelengths. Despite this color variation, humans only see stars as white because our eyes combine the various wavelength colors all stars emit.
Cavity With a Hole
A straightforward example of a black body is a cavity with a small hole in it. The light entering the hole undergoes so many reflections within the cavity walls that no light can ever be reflected out. If the walls are painted black, making them absorptive, the cavity represents a perfect black body.
A black hole is an area in spacetime in which gravity is so strong that nothing, not even light, can escape. Black Holes are as close to a perfect black body as black bodies come. They absorb all the light that enters the horizon but have zero reflectivity.
Black Body Radiation
The term “black body radiation” defines the relationship between the temperature of an object and the wavelength of electromagnetic radiation it emits. The quantity of radiation a blackbody will emit is determined by the object’s temperature, regardless of the object’s size or shape. A “perfect” black body absorbs and re-emits all radiation, no matter the wavelength spectrum. The waves cold objects emit have low frequencies, whereas hot objects emit waves with higher frequencies and visible light or ultraviolet.
All objects are black body radiators, as all objects emit electromagnetic radiation according to their temperature. A few common day examples of black body radiators which utilize their radiation for other processes or emit visible light are:
- Electric heaters
- The stars and sun
- Incandescent light bulbs
- Warm-blooded animals
- Burglar alarms
The Emissivity of a Black Body
Emissivity is the ratio of the radiation emitted from an object to the radiation emitted from a blackbody when the temperatures and wavelengths are under the same viewing conditions. Emissivity is characterized as a number between zero and one. Zero represents a perfect reflector, whereas one represents a perfect emitter. Because black bodies are perfect emitters, or as close to perfect emitters as an object can be, they have an emissivity of one.
Understanding emissivity is a critical part of calculating reliable non-contact temperature measurements and carrying out heat transfer calculations.
One example of how emissivity can be used is during the process of launching vehicles and satellites into space. Companies, such as Acktar, use their understanding of black bodies and emissivity to create emissivity coatings which protect spacecrafts during atmospheric re-entry.
Using Black Bodies to Develop New Technology
The knowledge of black bodies and black body radiation has been a pivotal tool in the exploration of physics. In 1918 Max Planck even won a Nobel prize for using blackbody radiation to pave a path towards understanding quantum theory. Today, black bodies can be used for a range of projects and experiments including, heating, security, thermal imaging, lighting, and black or thermal coatings. They can also be used for measuring and testing applications such as radiation thermometers. Furthermore, black bodies have recently been adapted to progress climate change research.
Acktar Black for Black Bodies
The uniquely high emissivity of Acktar black coatings make them the coating of choice for black bodies. The fact that the emissivity is essentially constant over a broad range of wavelengths makes the coatings uniquely suitable for calibration black bodies – one of the largest black body application areas.
The Acktar coating process is environmentally clean and no acids or other harmful materials are used.