Questions tagged [absorption]

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

Atoms and molecules can absorb electromagnetic radiation in many different ways. The transitions between rotational, vibrational, electronic and nuclear states are some of the possibilities. In a magnetic field, nuclear and electron spin states may also be quantized, so transitions between these states are possible.

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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 yellow pigment reflects only yellow light, but the…
David A.
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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 tells me it must turn into something or other, not…
user3932000
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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, reflection and absorption is as follows: transmission…
Ultralite
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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
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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 and dry again! I was wondering why the board is…
Yababaa
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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 is not the case, so what actually makes water a…
ryani42
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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 readily that we need often use lead to absorb it?
CognisMantis
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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 ceiling are made entirely of mirrors, with a single…
Adrian Petrescu
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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 why does it fade away to a complete darkness at…
Snack Exchange
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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 $\omega$ equal (or sufficiently close to) the…
Emilio Pisanty
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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 could think up were: For some reason, sound waves…
Nick Van Hoogenstyn
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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 is supplied with light that precisely matches the…
Gerard
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Why does skin-sparing occur in photon travel through material?

I'm taking a course on medical physics, and our lecturer has told us that the energy deposted as a function of distance of photons is zero right at the surface. Apparently, this phenomenon is called 'skin sparing'. You can see it in this plot…
Jack
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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 that the case?
Ashwin
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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 lines at those frequencies, because the relaxation of the…
macco
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