Absorption Definition and 534 Threads

Black hole is considered an almost ideal black body by being a perfect black hole. But does it ideally absorb everything coming in the vicinity of its impact? Is it really possible for anybody to either ideally absorb or ideally radiate energy?

A friend of mine heard a popular science show on the radio. A caller asked what is better to wear on a hot day, white clothes or black clothes. The answer given was that it did not matter because although black absorbs more readily it also radiates it more readily. My friend said of course that...

Hi, I have a question. If a crystal absorbs light and the absorption process leads to some excess energy being released as heat . Can one calculate the temperature rise or an experiment would most certainly need to be done? Apart from the heat capacity of the crystal before light absorption...

Hi, I have a tricky question regards the absorption of photons by semiconductor. Say I got a piece of semiconductor with Eg=4eV. Inside the bandgap, there are two defect levels, and each of them have a trapped electron. One of the defect has the energy level that is 1eV below conduction...

From this article on the monitoring of the solar Lyman Alpha emission line, a diagram (attached below) shows the 'mother of all absorption wavelength measurements': namely the geo coronal absorption of solar Lyman Alpha radiation at 1215.664 A or 121.5664 nm. Is this still the most accurate...

I am reading the text 'thermal radiation heat transfer' by Howell et al. (2011). In it they describe normal spectral emission by an isothermal volume element dV as 4\pi \kappa_\lambda I_{\lambda b}(S)dVd\lambda where \kappa_{\lambda} is the absorption coefficient and I_{\lambda b} is the...

In modern nanotechnologies, metals can be vapourized to coat onto the surface of another material as a thin but hard protective layer. How much energy would it take to heat 0.55 kg of iron from 1400oC to vapour at 2050oC?

What happens on the atomic level when light is reflected or refracted? Also why do some objects absorb light as heat?

Hi I want to ask which of the cast steels or forged steels provide with better shock absorption? The component has to be used in the under chassis of heavy trucks in bumpy roads. Can anyone help me with that? Thank You

Hi All, Kindly find here 2 questions, i was wondering about: 1) Will (helium cooled) Mono C-silicon be able to absorb a high intensity laser of about 900-1100 nm ? 2) How can Ultra-violet and visible light cause rise in material temperatures. Thanks.

Hi guys I just wanted to make sure I was thinking about this the right way. So in indirect bandgap semiconductors absorption needs a phonon to assist the electron to the conduction band from the valence band because a photon has virtually no momentum and only contributes energy to the electron...

I mean the photoelectric effect of the hydrogen atom. It is weird. By the Fermi golden rule, the transition or absorption rate is proportional to the density of the final states. At threshold, the electron has zero momentum and thus zero density of state. Therefore, the absorption coefficient...

I am familiar with the explanations for atomic absorption and emission line spectra and how the existence of discrete, fixed energy levels can give rise to the absorption/emission lines that are seen at only very particular frequencies of EM radiation. However, I have no intuitive understanding...

I'm having a bit of trouble understanding this. I am going through the section in Griffith's regarding Einstein's Coefficients. For a system in equilibrium, the rate of particles undergoing emission needs to equal the rate of particles undergoing absorption in order to maintain equilibrium...

Please explain me 1. How Absorption and Re-emission happens in an atom 2. A common explanation that has been provided is that a photon moving through the material still moves at the speed of c, but when it encounters the atom of the material, it is absorbed by the atom via an atomic transition...

Hydrogen - Halpha cross section i need the absorption cross section for the absorption of an H-alpha photon by a hydrogen atom, in the correct state of course, which I'm pretty sure is neutral hydrogen, n=2. I am needing this for a project, so i also need a reliable source where this comes...

Hi I am currently trying to find the water absorption lines by using a Michelson interferometer, as a detector I am using an ocean spectrometer. The data obtained is thus the spectrum's "received" by the spectrometer. Am I right to assume that in order to find the absorption peak/peaks I should...

Hi I was wondering if anyone could tell me what gasses are absorbed between 800 and 1000nm wavelength and weather there is a book that lists all the gas wavelengths that can be absorbed in this region Thanks bertopolis

Hi, I am doing a drop impact testing on a football shin guard. I know how to find the impact force but how do I determine the energy absorbed by shin guard during impact?

I was doing my homework and really got stuck on one question. Not looking for just an answer as that is useless, I really want to understand how to do this problem as I have no idea how to involve some of the givens. UO_2 is a common fuel for reactors. If the fuel is enriched to 4 atomic percent...

Homework Statement In this lab various thicknesses of a few materials are placed between a source of gamma radiation and a couple different detectors. It is reasonable to assume that some small change in the thickness of the shielding would produce a proportional change in the intensity of the...

So I've searched all over the internet for an explanation as to why when light of a certain wavelength hits an object, it absorbs it or reflects it. The best answer I've found is some light is absorbed and turned into heat, some is absorbed and re-emitted in the same direction (transmitted) and...

Is it true, as someone says, that molecular hydrogen in its fundamental state don't (almost?) absorb in the frequencis of the Balmer series of atomic hydrogen emission spectrum? Thanks. -- lightarrow

Hello, I was wondering how one would be able to tell the difference between an object emitting a certain wavelength of the EM spectrum, vs. an object reflecting that same wavelength of the EM spectrum. For example: 1) Suppose I have an IR source at 7 microns. I point this source at water, and...

Hi I am looking at the problem of optical absorption in direct gap semiconductors. It seems like the perturbing Hamiltonian is an oscillating perturbation , ie. an electromagnetic wave. Why can't the problem be treated as the absorption of a single particle , ie. a photon ?

I wrote a wave equation simulation in C# a while ago, and while everything works fine, I am running into the expected problem that my simulation boundaries (ie the edges of the grid) reflect the waves coming to them. Obviously I want to keep the grid of reasonable size, so I looked into what...

excuse me if this is too basic question. why is it that black materials BOTH "absorb" and "radiate" more heat ( energy ) and white materials do it less. i mean is there a rule that any material absorbs and radiate heat in the same amount and can't absorb more (like black materials) and...

Hi All, I am in need to calculate the ultrasound (20MHz) absorption of particles (polystyrene of size 15 microns) in water. I tried to search in the internet, but couldn't find any simple analytical expressions. Can someone please help me ! Thanks in advance! Regards, Radel...

Homework Statement In the photoelectric effect, it is assumed that a single electron absorbs a single photon. But, there is a certain probability that a single electron may simultaneously absorb two identical photons from a high-intensity laser. How would such an occurrence affect the...

Greetings, i need the absorption cross section for the absorption of an H-alpha photon by a hydrogen atom, in the correct state of course, which I'm pretty sure is neutral hydrogen, n=2. I am needing this for a project, so i also need a reliable source where this comes from. Thanks beforehand...

I understand photon absorption/emission by electrons in atoms, that transition them between energy levels, producing sharp spectral lines. However, I am having difficulty understanding photon absorption/emission by the vibrational and rotational modes of molecules, with respect to black body...

Hello, hello, I ask you to tell me the difference between the "absorbance" calculated from the dielectric function, and the "absorption cross section" calculated from Real-time TDDFT. is that they can give the same appearance spectrum? Thank you very much

As far as I know, bremsstrahlung radiation -especially cyclotron- can be absorbed by the plasma but it escapes because it is not dense enough etc. Have researchers tried to make lithium blankets reflect those radiations and trap the radiation inside, eventually increasing the absorption rate...

If the hydrogen gas is supposed to emit photons when the electrons undergo excitation, then why did the gas absorb energy earlier and got the electrons excited?

https://www.physicsforums.com/attachments/74483 https://www.physicsforums.com/attachments/74483 Based in the absorption spectra above, why is 595 nm the best wavelength to measure protein concentration with Bradford dye (Hint: there are two important reasons for choosing 595). I think it has...

I read in some place that the mirror be it 100 per cent reflective, will also absorb if a light strikes to it. Is it true? what does it absorbs?

I understand obviously that the image and light will be kept but it will become a little bit green. But what happen in a very specific way especially about absorption??

I recently thought about this. Let's say there's a hydrogen-like atom with a transition energy \omega. If it is hit with a photon of frequency \omega, it will make a transition to the excited state, so the change in internal energy is \omega. But by conservation of momentum, the atom will also...

Dear all, I would to like to ask do anyone have any idea on how to increase the COP and SCP(Specific Cooling Power) of a silica gel absorption chiller? COP= Heat removed by evaporator/ Heat supplied to system( normally is the hot water supplied to the absorption bed) SCP= heat removed at...

I saw this on Wikipedia http://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water Isnt it supposed to less than 1 ? maybe it has something to do with the unit ..why is it in m^-1?

Why are absorption cross sections for atoms so much larger than that of molecules. For example, the absorption cross section for the D2 line in Rubidium is ~1E-9 cm^2. Specifically, the cross section is basically σ~λ^2 The absorption cross sections for say, I2, is 9 orders of magnitude...

Hi guys! I have come across a problem I can't seem to wrap my head around. I've learned that E.M. radiation can be propagated by discrete packets of energy , photons. Is the energy of each photon discrete, or can it have a continuous range of energies depending on its frequency? I would be...

Hey, Just doing some reading on this and I'm a little confused as to why absorption produces a progressive lengthening of a seismic pulse. Quote from the textbook "In general, the effect of absorption is to produce a progressive lengthening of the seismic pulse". I understand how the...

Any object can emit and absorb radiation and the power of emission can be represented by the Stefan-Boltzmann law: P=AεσT4 In many texts the net power radiated is the difference between the power emitted and the power absorbed: Pnet=Aεσ(T4-Ts4) where Ts is the temperature of surrounding...

I need help with something that i seemed to remember was fairly easy, but just can't seem to find the simple formula for: I have an amount of hydrogen atoms at a temperature of 10000 Kelvin. What percentage of them are ionised and what percentage of them are in the n=2 excited state...

hello, i need the values for the absorption cross sections of positive hydrogen ions for a specific set of wavelengths, Halpha to start with. At first i thought finding this on the web was easy, but turns out to not be trivial at all. If you can help me, i also need the (reliable) source...

Hello all, I had a question out of curiosity. Say you have a green piece of paper. This paper is green because it absorbs the wavelength of lights corresponding to the other colors of the visible spectrum and reflects (transmits) green light, thus appearing green. If one were to shine a laser...

Hello. I have a question. I have two glasses - one is full, one is empty. And I will take a long paper towel to them - the first end to full glass and the second end to empty glass to same height. A paper towel is absorbent. Water from full glass rises to empty glass. It will stop when the...

Please tell me about common materials which absorb IR sunlight radiation in the band of spectrum 1.1-2,5 microns and which will not allow the penetration of IR if some surface is covered with thin layer of them ?

Supposedly devices use special algorithms to determine specific things about an object by its absorption or reflection of light, how exactly would such equations work? (if this isn't calculus then please tell me and ill post it somewhere else, i wasn't sure what type of mathematics this would be)