|
TheCow
Stranger

Registered: 10/28/02
Posts: 4,790
Last seen: 15 years, 6 months
|
Physics of a mirror
#8314994 - 04/22/08 03:57 PM (15 years, 9 months ago) |
|
|
I thought itd be amusing to have a thread devoted to how a mirror works. The idea of this thread is that one person says something, the following person has to try and delve deeper into what the above person said, or introduce the next step physically if they cannot. The caveat is that if someone else can delve deeper, then the discussion has to resume from that starting point ignoring the work after it. Of course the work after it would apply once we delved deep enough into the subject at hand to move on. For instance we can simply say that light hits a mirror and gets reflected back, however the actual mechanism is much much deeper than this. Each post should be limited to a single point only.
I expect this post to get deep into the physics of light, matter interaction,theoretically one could talk about this from an electromagnetic standpoint with wavefronts, going into a more micro view we can discuss the quantum mechanical aspects of this by discussing dipole moments witha perturbing electric field. If anyone wants to go deeper they are welcome to.
Unfortunately I have an extreme amount of work to do this week and possibly next week so I wont be able to add too much to this thread until then, assuming I dont procrastinate. Its possible this thread will never take off like I imagine it might, but if it does we could develop a fully explained theory of a mirror.
By mirror I mean metal with a layer of glass on top
Just for background, I chose a mirror because it is a common item that people take for granted.
Anyways to start things off, light rays from the sun head toward a mirror...
|
Visionary Tools



Registered: 06/23/07
Posts: 7,953
Last seen: 1 year, 7 months
|
Re: Physics of a mirror [Re: TheCow]
#8315016 - 04/22/08 04:03 PM (15 years, 9 months ago) |
|
|
And then the photons bounce off. My theory is all those free electrons metals have make them shiny, as they bounce off the photons, compared to black items, which do not have many free electrons, and absorb photons.
Am I right? What am I missing out?
--------------------
|
TheCow
Stranger

Registered: 10/28/02
Posts: 4,790
Last seen: 15 years, 6 months
|
|
Let me explain further, take it one step at a time. For instance you could have said light hits the glass. Then someone else would talk about the refractive index change for example. Someone would explain the refractive index phenomena at a deeper level and so on, eventually we would make it to the metal
The idea is not to merely explain it at a superficial level, but to explain as many aspects of the action as possible. No real reason
|
Visionary Tools



Registered: 06/23/07
Posts: 7,953
Last seen: 1 year, 7 months
|
Re: Physics of a mirror [Re: TheCow]
#8315067 - 04/22/08 04:15 PM (15 years, 9 months ago) |
|
|
Oh, but there's lots of things I could mention about mirrors, and not just the physics behind them. I'm no good at those one sentence games.
--------------------
|
TheCow
Stranger

Registered: 10/28/02
Posts: 4,790
Last seen: 15 years, 6 months
|
|
Yea dont worry about one sentence. I just want to restrict this to one point. For instance if you wanted to talk about the refractive index, but had knowledge of how to define it immensely, then you would be allowed to present the whole of your derivation on the subject. I just dont want someone to talk about the refractive index, then talk about what happens after this. One idea per post. There is indeed a lot of interactions that most people do not think about, thats why I think this thread could get interesting
This is just a physics discussion however
|
sleepy
zZzZzZzZz


Registered: 01/17/05
Posts: 3,888
Loc:
|
Re: Physics of a mirror [Re: TheCow]
#8315368 - 04/22/08 05:36 PM (15 years, 9 months ago) |
|
|
i don't understand mirrors, glass, or computer/tv screens.
they are magical and the only explaination is we are in a matrix.
Edited by sleepy (04/22/08 05:56 PM)
|
TheWall
DayTripper



Registered: 04/02/08
Posts: 101
Loc: BigEasy
Last seen: 13 years, 6 months
|
Re: Physics of a mirror [Re: sleepy]
#8316041 - 04/22/08 08:00 PM (15 years, 9 months ago) |
|
|
So now that weve made clear that the photons bounce off of the mirror, now what? They enternally travel and bounce off things, considering they are at the speed of light? not quite sure how this topic works.
|
Epigallo
Stranger
Registered: 09/17/06
Posts: 8,155
Last seen: 6 years, 10 months
|
Re: Physics of a mirror [Re: TheCow]
#8321101 - 04/23/08 09:43 PM (15 years, 9 months ago) |
|
|
So now that weve made clear that the photons bounce off of the mirror, now what?
Some of the photons bounce off of the mirror at an angle of reflectance equal to the angle of incidence and some are absorbed and converted to heat due to the reflective index of the surface.
(moving along)
|
johnm214



Registered: 05/31/07
Posts: 17,582
Loc: Americas
|
Re: Physics of a mirror [Re: TheWall]
#8321915 - 04/24/08 02:42 AM (15 years, 9 months ago) |
|
|
Quote:
TheWall said: So now that weve made clear that the photons bounce off of the mirror, now what? They enternally travel and bounce off things, considering they are at the speed of light? not quite sure how this topic works.
I don't think this is what he's asking for.
he's askig step by step
So he said light heads towards a mirror.
The next step would be light contacts the mirror/ glass covering the metal.
I might participate if I can figure this stuff out, but I'm no good at physics
|
Cepheus
Balance




Registered: 04/19/06
Posts: 8,266
Loc: the space between reality...
Last seen: 1 year, 1 month
|
Re: Physics of a mirror [Re: Epigallo]
#8322933 - 04/24/08 12:11 PM (15 years, 9 months ago) |
|
|
I'm going to talk about the actual absorption:
All electromagnetic waves carry (?) energy, via Planck's E=hf. The absorption of electromagnetic waves depends on a key factor: The electron configuration of the atoms at the surface of a material. If the material has a lot of double bonds (which means delocalization of electrons) it will have smaller energy gaps which corresponds to smaller frequencies of light (again via E=hf). The area of a molecule responsible for its colour is known as the chromoaphor.
(now its time for some speculation):
Glass (generally) for the most part is a Sillicon Dioxide, with a few other transition metal elements thrown in the mix. It forms a giant covalent lattice, which has very large areas of delocalization (due to all of the double bonds; O=S=O ). This means the energy gaps between electrons will pretty damn small; which means that glass will absorb high frequency electromagnetic waves (which it does in the form of UV radiation).
As a mirror absorbs only high energy electromagnetic radiation, it reflects all of the visible spectrum back to our eyes hence why we can see everything.
The actual image reflected is to do with the refractive index of the glass and the coating material used, but that has already been mentioned.
-------------------- "I only ever hope to reach equilibrium, in Nature's matrix, in line with the meridian" ~ Jehst
"...and I know that I have to keep breathing, as tomorrow the sun will rise, who knows what the tide will bring?" Free Spore Ring Europe Send any spare spore prints you might have and help the distribution
Open Source. Freedom. GNU/Linux Addicting is not a word.
|
Epigallo
Stranger
Registered: 09/17/06
Posts: 8,155
Last seen: 6 years, 10 months
|
Re: Physics of a mirror [Re: Cepheus]
#8325204 - 04/24/08 10:37 PM (15 years, 9 months ago) |
|
|
The glass absorbs and reflects all wavelengths at exactly the same rate - at the speed of light, 3 * 10^8 m/s. The wavelength of each light wave determines how much energy is reflected or absorbed when it meets the glass. Using f = c/w (where f is frequency, w is wavelength, and c is the speed of light) and plank's equation E = hf, the amount of energy absorbed per photon in each lightwave can be calculated. These photons shake the glass molecules, generating a quantity of heat equal to their embodied energy.
|
2sky
a friend of Narnia


Registered: 08/08/07
Posts: 119
Loc: the Dawn
|
Re: Physics of a mirror [Re: TheCow]
#8340421 - 04/29/08 12:24 AM (15 years, 8 months ago) |
|
|
When you raise your right hand, why does the image raise it's left hand?
-------------------- To fly to the sun without burning a wing , and lie in the meadow and hear the grass sing - In Search of the Lost Chord / The Moody Blues - 1968 But for a tree to grow to the sky, it's roots must go to the very depths of hell itself - Tantra,the Supreme Understanding - osho
|
DieCommie


Registered: 12/11/03
Posts: 29,258
|
Re: Physics of a mirror [Re: 2sky]
#8340505 - 04/29/08 12:46 AM (15 years, 8 months ago) |
|
|
Thats a hard question to answer. Intuitively from the geometry, it makes sense right? Like if you face a person without a mirror, his left hand is in front of your right hand. There is a parity in the horizontal direction. BUT there is no such parity in the vertical direction. Why is there parity in one but not the other, when it seems all symmetrical. hmmm, I have to sleep on it
|
leoside
AKA cannon fodder
Registered: 01/18/08
Posts: 1,489
|
Re: Physics of a mirror [Re: 2sky]
#8340565 - 04/29/08 01:06 AM (15 years, 8 months ago) |
|
|
Quote:
Glass (generally) for the most part is a Sillicon Dioxide, with a few other transition metal elements thrown in the mix. It forms a giant covalent lattice, which has very large areas of delocalization (due to all of the double bonds; O=S=O ). This means the energy gaps between electrons will pretty damn small; which means that glass will absorb high frequency electromagnetic waves (which it does in the form of UV radiation).
Do you mean the gaps between the orbitals? If the gaps between the LUMO and the HOMO are small, as you seem to be suggesting, the compound should absorb light with longer wavelengths predominantly.
This is why normal, everyday, cheapass glass doesn't absorb UV radiation.
Hopefully I didnt just make the above up, it sure does make sense in my head 
Small energy gap --> absorb lower energy light
-------------------- I watched with glee While your kings and queens Fought for ten decades For the gods they made
|
Cepheus
Balance




Registered: 04/19/06
Posts: 8,266
Loc: the space between reality...
Last seen: 1 year, 1 month
|
Re: Physics of a mirror [Re: leoside]
#8341875 - 04/29/08 12:28 PM (15 years, 8 months ago) |
|
|
Yeah you're right. I get this confused quite regularly heh.
I'm glad you said this though, cause I have exams coming up and you just made me reinforce my knowledge .
More delocalization = more disorder = less energy required to excite = Smaller frequency = larger wavelength.
Glass doesn't absorb the visible spectrum though or infrared..
Well now I don't know what to think
-------------------- "I only ever hope to reach equilibrium, in Nature's matrix, in line with the meridian" ~ Jehst
"...and I know that I have to keep breathing, as tomorrow the sun will rise, who knows what the tide will bring?" Free Spore Ring Europe Send any spare spore prints you might have and help the distribution
Open Source. Freedom. GNU/Linux Addicting is not a word.
|
leoside
AKA cannon fodder
Registered: 01/18/08
Posts: 1,489
|
Re: Physics of a mirror [Re: Cepheus]
#8341991 - 04/29/08 12:57 PM (15 years, 8 months ago) |
|
|
I don't believe there are any available p-orbitals in the glass matrix (silica). I always saw it as sort of like polyethylene.. The monomer is unsaturated but the polymer contains no degrees of unsaturation.
There is no real delocalization of electrons in glass
The way they colour glass is by adding transition metal complexes.. then you can use crystal field theory pretty easily to predict the colour of the glass.
The lack of delocalization could mean that the gaps between the orbitals (HOMO/LUMO) is quite large and nothing that we are really concerned about should be absorbed
-------------------- I watched with glee While your kings and queens Fought for ten decades For the gods they made
|
deimya
tofu and monocle



Registered: 08/26/04
Posts: 825
Loc: ausländer.ch
|
Re: Physics of a mirror [Re: leoside]
#8342235 - 04/29/08 02:21 PM (15 years, 8 months ago) |
|
|
Mirrors are mostly made out of shiny metals. The glass only serves as a protector and transparent medium. Conduction electrons in metals behave roughly like a free electron gas. When you shine light on a metal you are applying an oscillating electric field upon this electron gas. Currents are thus induced at the surface and depending on properties of the metal these currents penetrate more or less deeply into the metal. If the penetration length is of the order of the thickness of your metal then it is transparent. For example silver is transparent in the ultraviolet range and above. If it is not, then the electron gas is effectively shielding the radiation propagation into the metal and instead reemitting, at an angle if it is the case, the radiation. The exact process might be interesting to look at.
Normally, metals are shiny for all frequencies under their plasma frequency. This plasma frequency is the frequency at which the whole electron gas is oscillating through the creation of a dipole between the (fixed) positive ionic core crystal and the collective motion of the electron gas. The fact that the reflectivity for frequency lower than the plasma frequency is virtually perfect explains the color of metals (not every of them, gold is special for example). Since the plasma frequency for copper is in the middle of the visible spectrum, the higher frequencies (green, blue, etc) are absorbed while the lower ones are reflected. Copper is thus reddish. The plasma frequency of silver is in the ultraviolet range and silver therefore appears to be a very good, "white" mirror for the whole visible spectrum.
In short, the mirror effect arises from the behavior of an electron gas at the surface of metals.
|
Baby_Hitler
Errorist



Registered: 03/06/02
Posts: 27,587
Loc: To the limit!
Last seen: 35 minutes, 57 seconds
|
Re: Physics of a mirror [Re: DieCommie]
#8342675 - 04/29/08 04:40 PM (15 years, 8 months ago) |
|
|
Quote:
DieCommie said: Thats a hard question to answer. Intuitively from the geometry, it makes sense right? Like if you face a person without a mirror, his left hand is in front of your right hand. There is a parity in the horizontal direction. BUT there is no such parity in the vertical direction. Why is there parity in one but not the other, when it seems all symmetrical. hmmm, I have to sleep on it
Consider this, if the mirror is on the floor or ceiling the person in the mirror is upside down. The plane of symmetry is dependent on the angle of reflection.
-------------------- Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ Ƹ̵̡Ӝ̵̨̄Ʒ (•_•) <) )~ ANTIFA / \ \(•_•) ( (> SUPER / \ (•_•) <) )> SOLDIERS / \
|
johnm214



Registered: 05/31/07
Posts: 17,582
Loc: Americas
|
Re: Physics of a mirror [Re: DieCommie]
#8344775 - 04/30/08 01:14 AM (15 years, 8 months ago) |
|
|
Quote:
DieCommie said: Thats a hard question to answer. Intuitively from the geometry, it makes sense right? Like if you face a person without a mirror, his left hand is in front of your right hand. There is a parity in the horizontal direction. BUT there is no such parity in the vertical direction. Why is there parity in one but not the other, when it seems all symmetrical. hmmm, I have to sleep on it
cuz left and right aren't independantly defined, they're relative to the refrence point. So from you're perspective, it IS the same hand that is raised in the mirror. The only anomaly is when you use a different refrence point for each measurment, i.e. this guy's left vs. my right, when really both directions are the same, i.e. to the north of the plane of the mirror.
|
leoside
AKA cannon fodder
Registered: 01/18/08
Posts: 1,489
|
Re: Physics of a mirror [Re: 2sky]
#8344786 - 04/30/08 01:21 AM (15 years, 8 months ago) |
|
|
Quote:
2sky said: When you raise your right hand, why does the image raise it's left hand?
Don't you know our universe is in enantiomeric excess to our mirror world?
-------------------- I watched with glee While your kings and queens Fought for ten decades For the gods they made
|
|