So why can't metals be transparent, some of their salts and compounds are?

It is the Atomic structure, size, resonant frequency, and manufacturing process. Salts are more likely to crystallize and form a patterned molecular structure which readily allows light to pass.

The large dense molecules of metal elements absorb or reflect light waves.

To allow light waves to pass you must have more of a crystalline structure, a loose atomic structure, or the ability to absorb light and re-radiate in the same frequency band.

The manufacturing process will determine the layout of molecules. A cast will have a random structure . Any rolling etc. only elongates this random structure.

One problem when you crystallize metal, is that it becomes brittle and loses its strength from its normal flexibility or ductility.

You would need to find a process to control the molecular structure and still maintain its strength. This is a partial paradox since most structured molecules are stiff. You will probably need to create a very long molecule alloy that has similar properties to clear plastics. The molecules are so long that they form patterns when melted and formed.

Thanks techno.

But metals are crystalline, body centered cubic, face centered cubic, close packed hexagonal. We did xray work to show this. So its not the crystal thing, although glass is not a crystal, and it is transparent...

"One problem when you crystallize metal, is that it becomes brittle and loses its strength from its normal flexibility or ductility." _ I'd love to get your reference for this- as when I was an undergrad we were working on growing single crystal jet engine turbine blades. They were'nt brittle, and they were single crystals. spring fractures look crystallized, but that is evidence of preexisting structure, not a new one.

I'm not sure I know what you mean by molecule, metals are generally discrete atoms rather than molecules. and those atoms are the same size and density in the transparent salts and gemstones I mentioned.

Thanks for trying. I'm hopeful somebody out there has an answer.

This one has me baffled. What material properties/attributes are associated with transparency?

milo

Cant give you a reference - Based on seeing metal crystallize with old age in ships.

Molecules- Alloys or metals with impurities. Maybe since the salts grow, there are no impurities.

I was just surfing the contents of CR4.......

and your comments.....Based on seeing metal crystallize with old age in ships

In my college course in Physical Metallurgy this was known as work hardening, The professor used the movie "For a few dollars more" with Clint Eastwood to demonstrate this. Commonly and incorrectly referred as Metal Fatigue.

p911

The physical properties of a crystalline material depend, to a large extent, on the spatial arrangement of atoms inside it - that is, on the crystal structure.

If you look at glass, you will notice that the bonding forces between the individual atoms is somewhat lower than in metals and this results in a longer distance between the individual atoms. On top of that if each atom only wants to bind to another atom on 3 of its 6 sides (only for arguments sake, not really glass), you will find that each atom is not so densely surrounded by others.

If you now look at metal, you will see that the crystal structure is still there, like stacking cubes repeatedly, but the linkages are shorter and there seem to be more other atoms binding with each-other which densely surrounds the inner atom.

glass

metals

enlarged piece

I hope this explains in really simple terms, I am only a simple boy, how some crystals are opaque, some translucent and some totally transparent.

Hey case491. Thanks for the response.

Bond length/interatomic distance/spacing seems to make sense.

You are dead on on the metallic crystal structure.

However, as the same metallic atoms are in the translucent salt of the metal, we need to find out if the bond length differs for that molecule rather than the pure metal?

Actually, in the salt the bonds are ionic, rather than metallic.

More to think about. its been too many years since chemistry. thanks for the very effective illustrations.

milo

HoooLyyyy..!

So technically the bonding stuff are a lot stronger attached it one each other. Awesone and well explained, much appreciated.

Really,

MC

Any metal is transperant when in very this foil shape.

But when we put many such thin foils together, it becomes opeque.

Doesn't it mean that the interatomic spaces of one thin foil fall against atom in another foil? May be this is what happens with no physical foils, but block of metal?

Metals are not transparent because the free electrons in their structure reflect light. The electrons have a wide range of energies and reflect a wide range of colours and therefore appear "silver" Gold misses a band and looks yellow, but still is shiny and metal like.

Salts do not have free electrons, and can transmit light. The electron that would have been free in the metal state is bound to the non metal anion in the salt.

I poked around a little and found a couple links with interesting perspectives.

http://arstechnica.com/journals/science.ars/2006/8/7/4905

http://www.cheresources.com/transmetalzz.shtml

http://www.sspectra.com/designs/TransMetal.html

Hi Milo, you are a fast keyboard-gunman than me (perhaps is the time lag).

Well, I'll try to put a bit more confusion:

1. Properties of metal salts are different from pure metals (not only the refraction index). In salts it's right to talk about "molecules".
2. Regarding atomic/molecular structures: what about polymers? None of them have free electrons like metals and some are transparent, some translucid and others opaques.
3. It's curious but is a fact that more amorphous structure of polymer results in the more transparency and as more crystalline like structure (ordered) more opaque.
4. It seems that doesn't fit in well with the previous answers, doesn't it?

I'm going to wait with you for a general solution.

Cheers

Good morning Kwetz. Actually, Blink's first link in the post just above seems to help, but it describes the problem as being the mismatch of refractive index between air and metal, without explaining the how or why that that happens, -ie. why is that so for metals and not for glass. as richard feynman noted, just because something has a name doesn't mean we understand it.

I am hopeful that someone will give us an answer that tells how and why. We have had some valiant attempts. Your questions just add to the value of this thread. I thought the earlier post about free electrons might be close, but your polymer comment puts that hypothesis back on its heels.

milo

I haven't take a look on the link, but in plastics is so, in amorphous ones, the refractive index remains more or less constant through the thickness and thus are more transparent, when structure is partially ordered the plastic becomes translucid and finally opaque.

If it's a question really of difference in refractive index, then is the same as what happen in ultrasonic NDT, even both are a different type of wave (mechanical, not electromagnetic as light) both comply with the reflection, refraction laws (Snell's law included).

In the ultrasonic waves, if you have a piece of material in the middle of some other ( a layer of air or water surrounded by steel or aluminum: A crack on those materials filled with air or water) the case is like the graph I'm trying to include:

T' is the percentage of wave pressure transmitted as a function of the frequency times the thickness (mm.MHz)

It's in Spanish, but sorry is my mother language and I'm a bit lazy to edit and translate the graph.

Any way there you have four curves the first two on the left are related to a layer of air (first in steel-"acero" and second on aluminum) and the two on the right part are equal bur the layer is water.

As you can see, if we take a normal ultrasonic frequency of 1 MHz to simplify,If the thickness of air is 10^-4mm or more, there is no transmitted wave either in steel or aluminum, but if the layer thickness is less than 10^-8mm, the percentage of transmission is 100%.

Of course transmission of sound between two material depends not only in the sound speed (similar to refractive index, which is the ratio between light speed in the material and in free space) but of acoustic impedance (the product of specific gravity of material times the sound speed)

For water case is the same but in a range of thicknesses a bit higher.

So, you see that a very thin layer of air between steel is "transparent to sound waves" but for thicker ones is "opaque".

I think isn't too bad comparison.

Cheers

Thanks for this. I am familiar with UT testing and you make a great case. SO how do we know if it is merely refraction, and again, why do metals refract different than other metal containing substances?

Thanks for responding.

Miles

AlO3 in amorphous state = Alumina. This is an ceramic material that is fully opaque.

In its single crystal form AlO3 = Sapphire. Which is completely transparent at visible wave lengths.

cURIOUSER AND cURIOUSER...

mILO

Yes, I know. But it doesn't invalidate what I posted that wasn't an assumption, it a fact in polymers. Salts or other inorganic compounds (most gems) behave in a different way and metals seems to behave different too.

But the transparency must have a common cause. I've read in some of the posts things about atoms/molecules arrangement, free electrons, etc. I'm sure that this have some effect on the optical behaviour of a material.

But I would put another bit confusion:

What we call "light" is just a small fraction of electromagnetic spectrum to which the human eyes react sending a signal to the brain which in turn identify the wavelength as a colour. But what about higher energy portion of electromagnetic spectrum? When wavelength is, say about 10^-12m (photon energy about 1 MeV), the nature of electromagnetic wave is the same and even the human eye cannot "see", a piece of steel 100 mm thick is "transparent". Just check it by placing a radiographic film on the opposite side (It's a fact too).

So even I'm a great ignorant, I've take a look on some links provided by Ken and it seems that extremely thin layers of metals (silver in the link) behave as transparent to visible light, so the general solution of the problem posted by Milo seems to be dependent not only on the refractive index, but on the wavelength of electromagnetic radiation (as in the ultrasonic similarity I commented before in another post) and I will bet that also to the relationship between the wavelength and structure of material.

Cheers

So, I guess the answer is that all materials are transparent at some frequency, just not necessarily in our limited visual spectrum.

The limitations are the space size, patterns of the structure, and angle of incidence.

The facts seems to demonstrate it both in mechanical and electromagnetic waves, but as I answered to another colleague in this thread, the main issue is still open: So why can't metals be transparent, some of their salts and compounds are?

I think they can with the right modifications.

They are transparent to different frequencies, Our perception is a small bandwidth. By changing the patterns and spacing of the atoms, you change what wavelengths are passed or interfered with.

If the wavelengths passed are in our perceptual range, we see it as transparent.

If the wavelengths passed are at the edge of our perceptual range we see it as opaque.

If the wavelengths passed are not in our perceptual range we see it as blocking the light.

To make Metals transparent we have to adjust the structure to pass frequencies within our visual bandwidth. Obviously the salts have a modified structure.

The tighter the structure, the higher the frequency must be to pass.

Hi, techno!

Outstanding observation, and well-put. It explains why metals are non-information-admitting to us (at least from their far side).

So now, since our perception capabilities are fixed without the assistance of artifical enhancers, and we really want to see those whales inside their aluminum tank, what must be done to the metal to make it transparent to us?

I think you're on the right track towards a solution. It seems to reside with changing the vibrational frequencies of metals to admit more information in our sensual ranges.

Perhaps this will require a molecular alteration, perhaps an atomic one. The two approaches are quite different, and I think the latter is the shortcut needed to achieve transparency. If the atoms of the metals can be rearranged, while maintaining their molecular identity, to admit frequencies within our sensing ranges, the metals can keep their innate properties and valued uses. How this might be achieved without allowing the metals to shred to bits due to molecular disassociation is an interesting question.

Special thanks to milo for bringing up the topic.

Mark

I don't think it is totally correct.

Opaque means no light comes through (in the visible wavelengths)

Opaque is the same as blocking the light in your terms. What you mean is translucent. And even then your description is not right as translucency lets part of the visible wavelengths of light through over the full range of those wave lengths but not all 100% of the transmitted light is passed through, only a proportion of.

You have now confused the concept of partially letting through the light in the full visible wavelengths with " only some wavelengths"

Thanks for your reframing the issue, Techno.

milo

Hi, Kwetz!

I think you've answered the question. We already know that metals are transparent. It just depends upon the strength and spectrum of the light wavelength passing through them. This brings to mind looking at a solar eclipse through a welding glass in order to keep its brightness safe at ordinary eyesight tolerances.

Opacity (and thus Transparency) seems to depend upon the amount of light resistance a substance possesses.

That being the case, Ohm's law or a variation thereof would seem to apply. Voltage could be supplanted by candle power (cp) to the integer represented by its wavelength (w), current by what? Lux? C²?, and resistance by an Opacity factor (O).

O = cp_w/C² or perhaps O = cp_w/L

Now we may be able to look at analogies in electricity to changing the resistance of a substance in order to render an opaque object transparent.

It's already been pointed out that dimension makes a difference. In that case, laws of thermodynamics might also apply. Two identically thin transparent layers of metal might inhibit the passage of light exactly 1.5 times as much as one.

Would temperature make a difference? Certainly a heated piece of metal begins to show the passage of infra red on the second side as it heats up.

Both of these conjectures regard metal in its altered-for-human-use molecular state. But it's been pointed out also in here that the structure of a transparent substance chain molecule has a larger interstitial volume. Would extending the molecular structure of manufactured metal make it transparent (short of blowing holes through it like swiss cheese )?

How about a process of alignment of the interstitial spaces? Can a magnetic metal be made transparent through an intensive process of depth magnetization (as compared to length or width magnetizing)? And if it could, would it have to be coated with a layer of glass or plastic to prevent it becoming permeable?

What kind of process might change metal's structure at the molecular level or even more basically? We already know how to affect the the processes of austenite and alloy.

How about a combination of some of the above processes? Super depth-magnetize a piece of metal that can then somehow be swollen or inflated to many times its normal size in order to stretch its molecular reaches, then slice it back to a useful size at the desired opacity.

Electrical engineers and nuclear physicists please have some fun with this. I just thought of a dozen really neat uses for it in addition to that mundane aquarium-izing of whales that everybody knows about.

Mark

as richard feynman noted, just because something has a name doesn't mean we understand it.

Feynman -- my hero.

I spend entirely too much time pondering why we see things, why we can't throw one material right through another, etc.

I've taken my kids on the 1000 meter walk, which gives one a good perspective on the tiny size of, and immense spacing between, the planets. Atoms are about 100 times less dense than our solar system, which has about the apparent density of a few grains of salt in a very large clean room. In my neighborhood, even with the planets laid out in line (a huge advantage for finding them) and even having placed them on the ground myself, if they were not marked by large cards, some of the smaller ones would be almost impossible to find on the walk back in toward the "sun".

As an adolescent boy, I wished my eyes were sensitive to xrays -- if they were, this would be a huge help in getting to know girls.

Thanks ken.

The x ray vision thing wouldn't be quite what you had hoped I'm afraid.

I can hear the locker room chatter, "did you see the three lobes of liver in her?" or "Checkout her femoral artery!"

There was a great line in one of the Dune books That I memorized: "Who knows what senses we lack that we might better see the world?" Are there similar invisible rainbows that would be apparent if we had increased spectral sensitivity?

Great response.

milo

In this book the transparency of gold leaf is discussed. When at room temperature gold leaf transmits green light, but at 250 C, it transmits white and is described as transparent.

I was looking for transparency of molten metals when I came across the above. Molten metals appear translucent or transparent, although I am not sure they really are. It would be easy to test with a larger puddle than I can create with my arc welder. I stumbled across a book from 1887 that debated the topic a little, although I didn't read much because my machine is acting slow.

The reason metals are not transparent is because the electron orbitals provide a conductance band (ergo conductors) and the surface eddy currents that are formed by photon adsorption keep light on the surface of the metal lattice....or something like that. This was all ,of what seemed like a rational explanation I got from a professor many years ago, that stuck.

I am not fully fluent in quantum mechanics, but it provides the best model for the interaction of materials with light. In the visible spectrum photons can be absorbed and emitted by electrons. Electrons in a conduction energy band in a metal have lots of available energy states to move into. Electrons in a semiconductor or insulator are more closely bound to their home states and have only a few bands to move into, and most of the energy gaps do not match the energy of visible light photons.

To find new insights, Google the color of metals. The color we perceive is based on the range of photon energies reflected by the metal.

One last insight. The refractive index of materials or even of free space is monotonic with the density of free electrons. I saw a report years ago postulating the use of explosives in orbit to create a cloud of free electrons that could be used to temporarily focus the light from a laser ... don't recall if it was a defensive or offensive weapons concept.

HAVE FUN

Hi, does it means that free space (no material) have a density of free electrons different from 0?

Great question!

The simple answer is No, free space does not have a high electron density ...although we are still trying to find the constituents of the dark matter.

The reality of plasma physics is that for every free electron there is a positive ion, usually an atom that is missing one or more orbital electrons, nearby. Any attempt to separate the unbound electron from a nearby atom must perform phenomenal work to overcome the electrostatic force of attraction between oppositely charged ions. As the electron has the smallest mass, by far, it is the particle that is accelerated through and by the local electric field.

I have not done the calculation, but was told by a respected nuclear physicist from Los Alamos National Laboratory that a mere 1 Farad of excess electrons on the moon would cause it to spiral out of its orbit and rendevous with the earth. This was his way of illustrating the remarkable balance of charge in the observable universe.

Back to the lens in space. An explosion would create a plasma cloud with positively charged nuclei and unbound electrons. Photons would interact with the electrons. Fairly quickly, the electrons would recombine with the positive ions and the refractive index would sink back towards unity.

Oh, and by the way, to this class of nuclear physicists, the refractive index is a complex number ... another feature I did not encounter in my physics courses while in undergraduate or graduate school many decades ago

I'll ask the dumb question that is on everyone's mind,

what's a Farad?

A farad is a measure of capacitance.

In electronic circuits, a Farad is a very large amount of capacitance. The black 1 Farad, 5.5V capacitor (2 cm in diameter or so) holds a very large charge in electronic terms but a very small charge in electromechanical terms. That capacitor would supply 2.75 volts x 1 amp for one second. A recent rechargeable AA battery is 2AH: 1.2 volts x 2 amps x one hour (3600 seconds!). So, you can see that a 1 Farad capacitor can store a tiny amount of "electricity".

When I found out how much a supercapitor able to accelerate my avatar vehicle just once to 60 mph cost, it brought tears to my eyes.

Thus, it is intriguing that such a tiny charge could dramatically alter the moon's orbit. I don't think I even understand the concept enough to comment on it.

I'll have to go back and read the post later, and sit in the corner and think.

More like go sit in a corner and cry.

Thats some incredible "balancing of forces."

Puts the idea of "tipping point" in a whole nother light.

So do you have links describing that avatar vehicle of yours?

milo

Some details on the vehicle are here:

www.gaiatransport.com

Hi, Blink!

As I was mentioning to the student who wondered whether mechanical or structural engineering was the right fit, "...make a contribution to the world".

You are.

Nice web site.

Mark

Added t o my favorites.

Some good thinking, my friend.

milo

You are correct ... I was in a hurry and meant to write Coulomb, not Farad.

Also, the little anectdote did not say how long it would take to deorbit the moon with the electrostatic force so created. I have not estimated that time, either ... but it is probably a short time on a cosmological time scale.

Well, I knew it even I'm not a nuclear physicist nor a specialist on dark matter, but just by intuition, if we assume matter and electromagnetic radiation are different forms of the same thing (a photon with an energy of few MeV in the vicinity of a nuclei field can transform in a couple of particles, 1 electron and 1 positron which in turn annihilate mutually giving a new photon), the dark matter I would bet is as electrically neutral as the known matter or otherwise we would have more knowledge about it.

But the main question posted by Milo and the additions made by myself are still open!

I don't get the Farad in the context you have used it is. The farad is defined as the amount of capacitance for which a potential difference of one volt results in a static charge of one coulomb. It has the base SI representation of s⁴ · A² · m^-2 · kg^-1. Since an ampere is the rate of electrical flow (current) of one coulomb per second, an alternate definition is that a farad is the amount of capacitance that requires one second for a one ampere flow of charge to change the voltage by one volt

This would mean that it equates to an amount of electrons that result in 1 coulomb of static current over one volt of potential. If this were to happen over one second you would have one ampere for one second over one volt.

Why do you then state the amount of electrons needed in Farad and not just in Coulombs?

One coulomb is a very large amount of charge, much larger than any seen in everyday experience. From Coulomb's Law one can calculate that two point charges of +1 C, one meter apart, would experience a repulsive force of 8.988×10⁹ N. This is roughly equal to the weight of 900,000 metric tons at the surface of the Earth.

This seems to already point to the attractive or repulsive force between the electrons, which is what you hinted at in your statement would knock the moon out of orbit. You therefor don't need to relate the unit to time or current (such as Farad), just stick with the amount of electrons needed or Coulomb!

Or do you think me wrong?

Refractive index is a complex number?? You mean... it's NOT the ratio of two speeds?? Or are you talking about the refractive index of your cloud of free electrons?

Also, while I'm at it, please explain the action of the 1 Farad of electrons on the moon that causes it to spiral out of its orbit.

The complex number carries the phase shift when it differs from 360 degrees for transmission or 180 degrees for reflection of a perpendicular incident beam. That is as simply as I can put it.

I already posted my apologies for typing Farad when I meant Coulomb ... perhaps others missed that pose as well. The 1 C charge imbalance causes the moon-earth capacitor to experience an electrostatic attraction. I also explained that this would not be a quick way to de-orbit the moon ... it is merely a convenience to illustrate the Exquisite balance of charge in the observable universe.

Thanks for asking for clarification.

Thanks for this.

milo

Dear Colleagues,

Suggest you look at the website found at the bottom of this post. It includes a remarkable photo named PLATE VIII. Antique engraved Czechoslovakian glass colored yellow with silver and red with gold (both Mie scattering from colloidal particles).

The web site discusses electron conduction bands in metals better than I did:

"When light falls onto a piece of iron, the electrons below the Fermi surface can also become excited into higher energy levels in the band by absorbing the energy from the light, as in Fig. 19, producing electron-hole pairs. The light is so intensely absorbed that it can penetrate to a depth of only a few hundred atoms, typically less than a single wavelength. Since the metal is a conductor of electricity, this absorbed light, which is, after all, an electromagnetic wave, will induce alternating electric currents on the metal surface. These currents immediately re-emit the light out of the metal, thus providing strong reflection of a polished metal surface.

The efficiency of this process depends on the selection rules that apply to the atomic orbitals from which the energy band had formed. If the efficiency of absorption and reemission is approximately equal at all optical energies, then the different colors in white light will be reflected equally well, thus leading to the "silvery" color of polished iron and silver surfaces. However, if the efficiency decreases with increasing energy, as is the case for gold and copper, the reduced reflectivity at the blue end of the spectrum results in yellow and reddish colors, respectively.

The colors of alloys follow a similar pattern, but are difficult to predict a priori. For example, the addition of 25 percent silver to pure gold produces a green alloy while a similar amount of copper produces a red one.

The direct light absorption of a metal in the absence of reflection is observed only in rare instances. Gold is so malleable that it can be beaten into gold leaf less than 100 nm thick, then revealing a bluish-green transmitted-light color. When gold is in metallic colloidal form, however, as in the 10-nm-diameter particles in "ruby glass," the very complex "Mie scattering theory" has to be used to explain the unexpected red color"

http://webexhibits.org/causesofcolor/9.html

Hi, jcrock!

"The light is so intensely absorbed that it can penetrate to a depth of only a few hundred atoms, typically less than a single wavelength. Since the metal is a conductor of electricity, this absorbed light, which is, after all, an electromagnetic wave, will induce alternating electric currents on the metal surface."

Which is the caressing effect of magnetron-emitted photons in the microwave. The photons caress the metal surface and brush the current off on the sharp edges of metal foil, fork tines, and sharp knife blades in the form of sparking. Something similar may occur in conductive crystals with sharp or ragged edges exposed to either rf or emf radiation. At constant frequency, the rf sparking is predictable because regardless of the currency increases in the gain, the frequency remains stable. The emf is not predictable because it oscillates with the gain.

Mark

MarkTheHandyman: I am a recent import to CR4, and am enjoying it very much so far. I am uncertain of the courtesy of replying to a post a year old... If this is considered inconsiderate or rude, please forgive me.

I find your quote regarding EM waves absorbed and converted to current to be fascinating. There are several posts orbiting around this idea, but no others reflect (pun unintended) nor illustrate my thought as well as yours.

I have been involved in the construction of several building that were 'Electromagnetically Non-transparent'. The facilities were for the tuning of Munitions Targeting radars, Flight radars, Voice/Data transmissions, as well as transmitter equipment for varied radio and radar equipment. All facilities have been on active USAF Airbases around the midwest. The need for such a facility is to be certain the tested equipment is receiving ONLY the test signals, and any transmitted EM radiation is contained inside the facility.

This was accomplished by surrounding the building (all 6 sides) with some type of a bronze cloth, and to Earth Ground this wrap at several places around the facility in a sump of high-carbon imbed (I once saw the contractor use bags of Kingsford Charcoal!).

This seems to be a paradigm of practical application of your quote in your post.

Fascinating!

Hi, Doorman!

Welcome to CR4! I hope you cintinue to find it a very interesting place on all kinds of levels.

No, there is no time limit for participating in older discussions. Many of us keep old discussions with a strong interest level on file just in case somebody has something to add later.

That's quite a solid RF cage you fellows built around your calibration plant.

Mark

Cool. The color theorie makes sense. but now the reflection process

"will induce alternating electric currents on the metal surface. These currents immediately re-emit the light out of the metal, thus providing strong reflection of a polished metal surface."

is what i'm fighting. You seem to be saying that reflection is not reflection at all, its re-emission.

I need a tums.

milo

Before I discuss your re-emission question, please let me reiterate that there are legions of folks in this world who profess and do understand quantum theory better than I. Perhaps one of them will jump in here and help all of us!

That said, the micro-model of reflection, refraction, absorption, scattering, photo-electron emission (and all other photon-electron interactions) includes an absorption and an emission event for each photon. When re-emitted at the same frequency the emitted photon maintains the same color and we say it has been reflected or refracted (the light ray bends, as in a prism or raindrop). When re-emitted at a lower frequency (red-shifted) the departing photon has less energy than the incident photon and under conservation of energy, the difference was used to excite an electron somewhere (leading to heating in the material that is doing the absorption).

I understand why you may be fighting this. The estimated size of an electron is several orders of magnitude smaller than a wavelength of visible light. On a macro-scale absorption tends to be maximum when the size of the irradiated body is ~ 0.4 wavelengths. At first blush, it is a surprise that absorption occurs at all. On second thought, the wavelength of AM radio waves is on the order of a kilometer, yet pocket radios do fine with an antenna about 3 inches long. The secret here is that the antenna is a ferrite rod with a coil wound around it in parallel with a capacitor that tunes the resulting resonant circuit to the frequency of the incoming wave. The resonant structure acts as a "flux sucker" concentrating the energy from the travelling AM radio wave into current and voltage that can be amplified by the radio.

Resonant absorption/emission is behind the colors in dyes, paints, crayons and nature. The shiny reflection of polished metal is due in part to such behavior and in part to the collective reaction of the electron cloud in the conduction band of the metal ... a place where the electron wavelength covers many lattice spacings and can match the wavelength of visible light.

I sort of glossed over it above, but Plank's constant links photon frequency to photon energy: E = h * f.

I leave you with this thought:

ALL MODELS are WRONG ... MOST are USEFUL

I am grateful for your patience and typing as well as your ability to get this into a digestible (or at least more easily chewed) form. Using the am antenna as analogous to matters of scale helps, I too made some coils of doom for cat whisker receivers once upon a time. The blue blades were the best.

My kudos.

milo

Just as an aside, The University of Dayton, in conjunction with the Army, Air Force and Raytheon has developed a process to make transparent Aluminum Oxy-Nitride sheets for use as ballistic windows in APC's and aircraft. it is 1/3 or less the thickness of the equivalent ballistic laminated glass window.

http://redinktexas.blogspot.com/2006/01/i-would-like-to-buy-some-transparent.html