Questions tagged [absorption]

A transition by which the energy of at least one photon is completely transferred to a material.

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Why does a yellow object turn white under a yellow light? Shouldn't it turn yellow instead?

Recently I was eating a yellow rice for lunch in a restaurant with only yellow lights. But the rice looked white! I was intrigued by this because I always thought it should look yellow since the ...
David A.'s user avatar
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How can an object absorb so many wavelengths, if their energies must match an energy level transition of an electron?

I believe I have a misunderstanding of some principles, but I have not, even through quite a bit of research, been able to understand this problem. My current understanding of transmission, ...
Ultralite's user avatar
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6 answers
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Where do photons go when they are absorbed?

The answer I usually get (and I'm paraphrasing here) is that they disappear and are instead absorbed as heat energy. But I find it hard to believe that the photon simply "disappears." Common sense ...
user3932000's user avatar
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43 votes
10 answers
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Why can't we see gases?

I am not sure what causes gas molecules to be invisible.This question may look silly but I really want to know the story behind it.
Praveen Kadambari's user avatar
35 votes
3 answers
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Why does a blackboard dry very quickly?

When you have made some stupid mistakes on a blackboard, you quickly want to erase it with a wet sponge before anyone sees them. So you clean the blackboard and within a minute the blackboard is clean ...
Yababaa's user avatar
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34 votes
4 answers
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Why is water a good neutron absorber?

I've seen this question asked multiple times, and the answer is never detailed. I initially assumed that either hydrogen or oxygen had relatively large neutron absorption cross sections, however that ...
ryani42's user avatar
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29 votes
1 answer
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How are photons "consumed"?

I have very little background in physics, so I apologize if this question is painfully naive. Consider the following thought experiment: an observer is in a closed room whose walls, floor, and ...
Adrian Petrescu's user avatar
29 votes
2 answers
6k views

Why do X-rays go through things?

I always heard that the smaller the wavelength, the more interactions take place. The sky is blue because the blue light scatters. So why is this not true for X-rays, which go through objects so ...
CognisMantis's user avatar
24 votes
4 answers
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Why can't sunlight reach the very deep parts of an ocean?

Sunlight reaches the surface of the ocean and refracts. So it is still there. And its speed is about $225000$ km/s in water which is still incredibly fast. Light is a massless electromagnetic wave. So ...
Snack Exchange's user avatar
23 votes
7 answers
57k views

Why do bass tones travel through walls?

I was in the shower while my roommate was listening to music and got to thinking about the fact that I could only hear the bass and lower drums through the walls. Why is this? The two possibilities I ...
Nick Van Hoogenstyn's user avatar
22 votes
3 answers
6k views

Why do lines in atomic spectra have thickness? (Bohr's Model)

Consider the atomic spectrum (absorption) of hydrogen. The Bohr's model postulates that there are only certain fixed orbits allowed in the atom. An atom will only be excited to a higher orbit, if it ...
Gerard's user avatar
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How does one account for the momentum of an absorbed photon?

Suppose I have an atom in its ground state $|g⟩$, and it has an excited state $|e⟩$ sitting at an energy $E_a=\hbar\omega_0$ above it. To excite the atom, one generally uses a photon of frequency $\...
Emilio Pisanty's user avatar
16 votes
4 answers
5k views

Why do colours of object change due to incident light?

A leaf is green, a pen is blue and so on because those objects absorb all colours and reflect only one colour. However when red light is incident on these objects, their colour becomes reddish. Why is ...
Ashwin's user avatar
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14 votes
3 answers
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Why don't absorption and emission lines cancel out in our Sun?

I was looking at this answer on why absorption lines and emission lines don't cancel out: An experiment shining light on the material and looking at the reflected spectrum will see absorption ...
macco's user avatar
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12 votes
2 answers
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How does a spectral line tell us about the magnetic field of a star?

An absorption line in the spectrum can indicate the abundance of a chemical element in a star; but according to NASA, it can also tell us about the magnetic field of the star. Can a spectral line ...
user6760's user avatar
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11 votes
1 answer
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Understanding the virtual states referenced in multiphoton absorption studies

The Heisenberg energy-time uncertainty tells us that we can have so-called virtual states between eigenstates as long as the lifetime of these states is at most: $\tau = (\frac{h}{4 \pi E_v})$ Where $...
RGrey's user avatar
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2 answers
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Why do you only hear the bass when someone nearby is wearing earphones?

When someone nearby is listening to music through earphones or headphones, usually you can only hear the bass (unless it’s really loud, where you can hear the singer and the other instruments too). ...
hb20007's user avatar
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Absorption of dark matter by black holes

Our Universe consists of about 22% Dark Matter (DM). Such matter is the main stuff of galaxies. Also, Black Holes (BH) live in galaxies. We know that DM is subject to gravitational interaction. So, ...
Sergio's user avatar
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9 votes
4 answers
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Why can Einstein coefficients be derived based on thermodynamically equilibrium relations when they are basically intrinsic?

Einstein coefficients for emission and absorption ($A_{21}$, $B_{12}$, $B_{21}$) are often derived from a consideration of thermodynamic equilibrium using Boltzmann statistics and comparison with ...
MichaelW's user avatar
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9 votes
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Can a photon be absorbed by a proton?

When incident light passes through a hydrogen gas, for example, does it have 50% chance (since it's a 1:1 ratio of protons to electrons) of getting absorbed by the proton? Any chance at all? If no, ...
Sparkler's user avatar
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9 votes
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What "happens" to the energy of a photon after it is absorbed?

The simple model of the colour of reflected light from objects (yes, colour perception is a function of the eye/brain) as I understand it is: Firstly I will write what I understand happens - which ...
Clive Long's user avatar
9 votes
1 answer
1k views

Shouldn't sound travel better through doors?

Sound travels much faster in solids than liquids and gases. Then why do we hear a fainter sound from the other room if we close the door than open it? As sound travels faster through solids......
MartianCactus's user avatar
8 votes
2 answers
2k views

What is cross section?

I am learning about unit Barn, it is a unit of cross section. I know it means how likely a particle is to interact with the material, it's like opacity or transparency in optics. What I don't ...
Soliton's user avatar
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8 votes
3 answers
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How does radiation shielding using absorbing materials work?

I understand that, for example, a thick enough sheet of lead can absorb gamma radiation, but I want to understand what actually happens at the molecular/atomic/subatomic level. Also, can the same ...
Icarus's user avatar
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1 answer
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How does the atmospheric UVB attenuation of terrestrial planets compare?

On Earth, UVB (280nm - 315nm or 320nm depending on the source) undergoes extensive attenuation through the atmosphere, when observed at the planet's surface, as illustrated below: Image source This ...
user avatar
7 votes
1 answer
967 views

Test whether a glass prevents you from getting your Vitamin D portion?

I work in an office with glass, which I believe filters the UV radiation of the sunlight. Is it possible to test if exposure to the light coming through the glass will supply Vitamin D for me as a ...
0x90's user avatar
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7 votes
3 answers
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Why are spectrums of incandescent light bulbs continuous despite the presence of Argon around them?

Incandescent bulbs emit light by heating a filament using electricity, this would lead to a continuous spectrum according to Kirchoff's first law. However, the glass casing around the filament is ...
Apporv's user avatar
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7 votes
1 answer
875 views

Could the solar shield on the James Webb telescope have been pitch black or does it need to be highly reflective?

When I look at pictures of the sun shield on the James Webb Space telescope (JWST), I see something that looks highly reflective (and hence must have a very low emissivity). My intuition tells me that ...
SalahTheGoat's user avatar
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7 votes
2 answers
600 views

How can absorption spectra form if atoms can't remain in an excited state?

I have been tasked to write a research paper on stars. However, I know very little about physics in general. I am learning about how we can glean information about stars by analyzing the light that ...
Luke's user avatar
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7 votes
3 answers
1k views

How precise must the energies match for absorption of photons?

According to Quantum Mechanics, in order for an atom to absorb a photon the energy of the photon must be precisely that of a "jump" between energy states of the atom. How precise must it be? If I ...
Tobias Tovedal's user avatar
7 votes
1 answer
807 views

Paint: "Darker When Dry"?

A great question I enjoy bringing up is why are things, in general, "darker when wet". This applies to porous and granular materials like wetted stone, paper, sand etc. It also comes up in ...
mittimithai's user avatar
6 votes
1 answer
314 views

Is there a zone where 'colour' overlaps between double rainbows?

Someone on social media posted this question based on a conversation with their (very cluey and creative) kid. Is there a zone between double rainbows where the 'colour' overlaps? This would be in ...
Errol Hunt's user avatar
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6 votes
3 answers
4k views

How do Black Bodies Absorb and Emit Radiation? [duplicate]

I have learnt how the gases of elements are able to absorb only certain wavelengths of EM radiation corresponding to the energy transitions between energy levels of orbitals. Furthermore, these ...
Nanoputian's user avatar
6 votes
1 answer
106 views

How do we know that the Sun is 71% Hydrogen by mass from emission/absorption spectra?

In my Intro to Astronomy ("intro" is very important, please keep responses as simple as possible) course, we're currently learning about light and electron orbitals and such, and I came ...
Sami Hanna's user avatar
6 votes
4 answers
5k views

Why can't electrons absorb any energy (i.e. absorb some energy of the photons necessary and emit the residual)?

Recently I had a question in mind about the absorption of photons. Why is it that only specific energy levels can be absorbed by electrons? I mean, I get the idea that electrons in an atom have only ...
Rab's user avatar
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6 votes
1 answer
124 views

How can daylight have a higher colour temperature (e.g. 6500 K or D65) than sunlight in space?

Supposedly, daylight at midday has a colour temperature of 6500 K. This reference is also the standard for calibrating computer screens (that's how I fell into this). However, outside the atmosphere ...
OsthatoAlfakyn's user avatar
6 votes
0 answers
581 views

Complex part of second-order susceptibility in nonlinear optics

In optics, the absorption of photons by a material can be described by considering the material's susceptibility. For linear absorption (involving a single photon), we think about the imaginary part ...
Liz Salander's user avatar
5 votes
4 answers
2k views

Aren't places where geodesics end singularities?

So of course when stuff falls into black holes, the geodesic for anything ends in that singularity. However, isn't it technically true that a light ray that originates from the sun and then hits the ...
MiltonTheMeme's user avatar
5 votes
2 answers
4k views

Different widths of spectral lines for different groups of stars

As seen in a Hertzsprung-Russell diagram, a specific stellar classification can correspond to more than one group/sequence of stars (a G5 star could for instance be either a giant, main sequence star ...
Jhonny's user avatar
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5 votes
4 answers
309 views

How to explain smooth absorption spectrum of nature (plants, etc.) while the atoms have discrete absorption lines?

From quantum mechanics, a photon of energy exactly equal $h\nu=E_2-E_1$ could be captured by an atom that has the energetic level levels $E_1$ and $E_2$ (with $E_1<E_2$). This corresponds to "...
Mathieu Krisztian's user avatar
5 votes
1 answer
1k views

How are problems in astronomical spectroscopy solved?

Astronomers based on the ground telescopes, watch the stars and make predictions about them based on the spectrum of light. But when the light from those stars reach the telescopes through the ...
Santhi Kabir's user avatar
5 votes
1 answer
2k views

Why are UV protective eyeware Orange?

Many industrial processes use uv as a curing agent. When one uses such a process, one must protect one's eyes from the radiation. Most uv protective gear I have seen is tinted orange? Does this ...
Cort Ammon's user avatar
5 votes
0 answers
83 views

What causes materials like Vantablack to have their high optical absorption properties?

As per the title of this post. From reading, I understand that blackbody radiation is a factor I should consider here, with light being absorbed and converted to heat etc. However, what I want to ...
Jenson Holden's user avatar
5 votes
0 answers
1k views

Absorption coefficient from HITEMP or HITRAN [closed]

How to calculate the absorption coefficient (for radiation) from HITEMP or HITRAN databases? Or where can I find some tables or plots for the absorption coefficient?
jokersobak's user avatar
4 votes
3 answers
4k views

Photoelectric effect absorption coefficient decreases with energy, why?

Consider the diagram below: (Author: Joshua Hykes source: Wikipedia) From this diagram we can see that the absorption coefficient for the photoelectric effect generically decreases with the increase ...
Quantum spaghettification's user avatar
4 votes
2 answers
3k views

Is a detailed absorption spectrum available for carbon dioxide from 300-1100nm?

I believe that carbon dioxide does not absorb light in the visible region, but is a spectrum available somewhere online that shows this as a fact? As in a straight horizontal line at 100% transmission?...
Slarty's user avatar
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4 votes
1 answer
656 views

Sunscreen protection, SPF, and amount applied: relationship?

In the article How SPF Changes with How Much Sunscreen You Use (last updated Dec 29, 2017), the author says that insufficient sunscreen disturbingly decreases protection exponentially, in other words, ...
ryang's user avatar
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4 votes
1 answer
4k views

What is absorption rate of WiFi and Bluetooth RF in water? [closed]

Specifically, frequencies 5.75GHz and 2.4-2.485GHz. I want to place a hermetically sealed circuit at the bottom of a gold fish bowl, and want to know if the water will significantly attenuate WiFi or ...
Doug Null's user avatar
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4 votes
4 answers
737 views

How can we prove that a photon is absorbed only once?

When I first heard about the photons and the double-slit experiment my immediate thought was the following: Alright, energy is not absorbed continuously but in discrete units, photons, but nature ...
Calmarius's user avatar
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4 votes
3 answers
1k views

A question about atomic clocks

I have a rather simple question about atomic clocks. I have read that: Microwave radiation with a frequency of exactly 9.192.631.770 cycles per second causes the outermost electron of cesium-133 ...
Bardo's user avatar
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