In the article, I try to tell why some substances are transparent for visible light, and others are not. Fully, this topic is very complex and goes into the most debris of physical processes, affecting optics, chemistry, quantum mechanics and many more adjacent disciplines and includes the output of the formulas and the divanctural matcharat. I consciously will make very wide assumptions, lowering 9 / 10x what is happening in the substance actually .

My goal is to tell so that it becomes clear to the schoolboy, who has not even began to study physics, i.e. Literally a five-grader.

So, as you know, all bodies consist of molecules, and molecules from atoms. Atoms are not difficult (in our promotion description on the fingers ™). In the center of each atom there is a kernel consisting of a proton, or a group of protons and neutrons, and around, round Electrons are rotated on their electronic orbits / orbitals.

The light is also pretty simple. Forget (who remembered) about the corpuscular-wave dualism and the Maxwell equation, let the light be a stream of photon balls, flying out of a flashlight directly to our eyes.

Now, if we put a concrete wall between a flashlight and eye - we will no longer see light. And if you delay a flashlight on this wall on our side - on the contrary, we will see, because the beam of light will affect the concrete, and will fall into our eyes. But through the concrete, the light will not go.

It is logical to assume that the balls - photons are reflected and do not pass through concrete wall Because they are fighting about the atoms of the substance, i.e. concrete. More accurately fighting about electrons, for electrons rotate so fastthat the photon does not penetrate the electronic orbital to the kernel, and bounces and reflects already from the electron.

Why light goes through glass wall? After all, inside the glass, too, molecules and atoms, and if you take a fairly thick glass, any photon should be encountered sooner or later, because the atoms are the same trillion in each grain grain!

The thing is as Electron collisions are occurring with photons. We take the easiest case, one electron rotates around one proton (this is a hydrogen atom) and imagine that by this electron shook the photon.

All photon energy has passed the electron. It is said that the photon is absorbed by the electron and disappeared. And the electron received an additional energy (which photon carried with him) and from this additional energy he jumped to a higher orbit and began to fly further From the nucleus.

The absorption of photon electron and the transition of the latter on a higher orbit

Most often, higher orbits are less stable, and after a while, the electron will empty this photon, i.e. "Let him go to freedom"And he will return to his low stable orbit. The emitted photon will fly in a completely random side, then it will be absorbed by another, adjacent atom, and it will remain wandering in the substance, as long as it will not be emitted back back, or will not ultimately be on the heating of the concrete wall.

And now the most interesting. Electronic orbits cannot be anywhere around atom's core. Every atom of each chemical element There is a clearly deterministic and finite set of levels or orbits. The electron cannot be slightly climbed above or drop down slightly. It can only jump on a very clear gap of up or down, and since these levels differ in energies, which means that only a photon with a certain and very precisely specified energy can push the electron to a higher orbit.

It turns out that if we have three photons with different energies, and only one it is exactly equal to the difference of energies between the levels of a particular atom, only this photon "collides" with an atom, the rest will fly by, in the literal sense "through atom" For it will not be able to provide an electron clearly specified portion of energy to go to another level.

And how can we find photons with different energies?

It seems that the more speed, the higher the energy, everyone knows, but all the photons fly from the same speed - the speed of light!

Maybe the brighter and more powerful the source of the light (for example, if you take an army spotlight, instead of a flashlight), the more energy will be at the photons? Not. In the powerful and bright beam of the searchlight, just a greater number of photon pieces themselves, but the energy of each individual photon is exactly the same as in those that fly out of a dead pocket lantern.

And here we will still have to remember that the light is not only a flow of particles balls, but also a wave. Different photons differ in different wavelengths, i.e. Different frequency of own oscillations. And the higher the frequency of oscillations, the more powerful energy charge carries the photon.

Low-frequency photons (infrared light or radio wave) carry little energy, high-frequency (ultraviolet light or x-ray) - a lot. Visible light - somewhere in the middle.

Here and lies the rays of the transparency of the glass!
All the atoms in the glass have electrons in such orbits, which, to move to a higher energy, the impetus is needed, which is not enough in the photons of visible light. Therefore, it passes through the glass, practically not facing its atoms.

But ultraviolet photons - quite carry the energy necessary to translate electrons with orbit into orbit, therefore, in ultraviolet light, ordinary window glass is completely black and opaque.

And what is interesting. Too much energy is also bad. The photon energy should be precisely equal to the energy of the transition between orbits, from which any substance is transparent for one length (and frequencies) of electromagnetic waves, and not transparent for others, because all substances consist of different atoms and their configurations, i.e. molecules.

For example, concrete is transparency for radio waves, and infrared radiation, opaque for visible light and ultraviolet, is not transparent as well for X-ray, but is again transparent (to some extent) for gamma radiation.

It is about this that it is correct to say that glass is transparent for visible light. And for radio waves. And for gamma radiation. But opaque for ultraviolet. And almost not transparent for infrared light.

And if you still remember that the visible light is also not all white, but consists of different lengths (that is, the colors) waves from red to dark blue, it will become about it is clear why the items have different colors and shades, why red roses, and violets - blue. But, this is the topic for another post explaining complex physical phenomena simple language Analogies on the fingers ™.

Look in the window. If we carry glasses, put them. Take binoculars and do not forget about the Lupu. What do you see? To ensure that you will not interfere with the numerous glass layers to interfere with your eyesight. But how it turns out that such a solid is practically invisible?

To understand this, you need to know the structure of the glass and the nature of its origin.

All begins with the earth's crust, which is mostly from silicon and oxygen. These elements are formed in the reaction of silicon dioxide, the molecules of which are built into the correct crystal lattice quartz. Crystal quartz in particular rich on the manufacture of glass sand. You probably know that the glass is solid and does not consist of small pieces of quartz, and this is not good.

First, the coarse edges of the grains and microdefects in the crystal structure reflect and dissipate the light falling on them. But if you heat the quartz to high temperatures, the molecules will begin to fluctuate more, which will lead to a break of the link between them. And the crystal itself will turn into a liquid, as well as the ice turns into water. True, with the only difference: when cooled back into the crystal, the quartz molecules are no longer gather. On the contrary, as molecules lose energy, the probability of ordering only falls. As a result, it turns out an amorphous body. The solid with the properties of the liquid for which the absence of intercrystalline boundaries is characteristic. Due to this, the microscopic glass acquires homogeneity. Now the light passes through the material almost freely.

But this does not explain why the glass misses the light, and does not absorb it like the rest of the solid bodies. The answer lies on a small scale, intraatomic. Although many are aware that the atom consists of a kernel and rotating around electrons, many are it known that the atom is hardly an ideal emptiness? If the atom was the size of a football stadium, then the core of the pea size in the center of the field, and the electrons would be tiny sands somewhere in the rear rows. Thus, the place for the free passage of light is more than enough.

The question is not why the glass is transparent, but why other objects are not transparent. The whole thing in the energy levels on which electrons are located in the atom. You can imagine them in the form of various rows at our stadium. The electron has a certain place on one of the rows. However, if he has enough energy, it can jump over to another row. In some cases, the absorption of one of the photons passing through atom just ensures the necessary energy. But here snag. To transfer an electron from a number to a row, the photon must have a strictly defined amount of energy, otherwise it will fly by. So happens with glass. The rows are so far from each other that the energy of a photon of visible light is simply not enough to move the electrons between them.

And the photons of the ultraviolet energy spectrum is enough, so they are absorbed, and here, no matter how try, hiding behind the glass, you will not contradict. In the century, which has passed from the production of glass, people completely appreciated him unique property Being both solid and transparent. From windows, grubning daylight, and protecting from the elements, to devices that allow to look far into space, or observe microscopic worlds.

Having deprived modern glass civilization, and what will remain from it? Oddly enough, we rarely think about how important it is. Probably, it happens because, being transparent, the glass remains inconspicuous, and we forget about what it is.

Keywords: Structure of glass, the origin of glass, science on the portal Experiment, scientific articles

There were times when tanned skin was considered a sign of low origin, and noble ladies tried to protect her face and hands from sunlight, in order to preserve the aristocratic pallor. Later, the attitude to the tan has changed - it became an indispensable attribute of a healthy and successful person. Today, despite the unsuspicent disputes regarding the benefits and harm of insolation, the bronze shade of the skin is still at the peak of popularity. That's just the opportunity to visit the beach or solarium is not all, and in connection with this, many are interested, whether it is possible to light through through the window glass, located, for example, on a swollen sun of a glazed loggia or attic.

Probably, every professional driver or just a person who spends a long time behind the wheel of the car, noticed that his hand and face brushes and face are covered with a slight tan. The same refers to the office employees, forced to sit all the work shift in the unblocked window. On their faces, it is often possible to detect tan tracks even in winter. And if a person is not a regulance of solarium and does not make a daily promenade in the parks, it will not be possible to explain this phenomenon through the glass through the glass through the glass. So does the glass misses the ultraviolet and is it possible to tan through the window? Let's deal with.

Nature Zagara

In order to answer the question whether it is possible to get a tan through the usual window glass in the car or on the loggia, you need to figure out how exactly the process of skin coverings occurs and what factors have an impact on it. First of all, it should be noted that the tan is nothing more than a protective reaction of the skin for solar radiation. Under the influence of ultraviolet cells of the epidermis (melanocytes), the substance melanin (dark pigment) is beginning to produce, thanks to which the skin also acquires a bronze tint. The higher the concentration of melanin in the upper layers of the dermis, the more intense it turns out the tan. However, this reaction is not caused by all UV rays, but only lying in a very narrow range of wavelengths. Ultraviolet rays are conditionally divided into three types:

• A-rays (long-wave) - Practically do not delay the atmosphere and unhindered reach the earth's surface. Such radiation is considered the safest for the human body, because it does not activate the synthesis of melanin. Everything that it is capable is to cause a slight darkening of the skin, and then only with prolonged exposure. However, with excess insolation, the long-wave rays are destroyed by collagen fibers and skin dehydration, as a result of which it begins to grow faster. And for some people, allergic to the sun is developing because of A ray. Long-wave radiation easily overcomes the thickness of the window glass and leads to a gradual burnout of the wallpaper, the surface of furniture and carpets, but it is impossible to get a full tan with it.
• In-rays (middle-wave) - They are delayed in the atmosphere and reach the surface of the earth only partially. This type of radiation has a direct impact on the synthesis of melanin in skin cells and contributes to the appearance of a rapid tan. And with its intensive effects on the skin there are burns of varying degrees. Through the usual window glass in-rays are not capable of penetrating.
• C-rays (shortwave) - Present a huge danger to all living organisms, but fortunately, they are almost completely neutralized by the atmosphere, without reaching the surface of the Earth. You can only encounter such radiation in the mountains, however, it is extremely weakened there.

Physics allocate another type of ultraviolet radiation - extreme, for which the term "vacuum" is often used in view of the fact that the waves of this range are completely absorbed by the atmosphere of the Earth and do not fall on the earth's surface.

Is it possible to light through the glass?

It is possible to get a tan through the window glass or not, directly depends on what properties it has. The fact is that the glasses are different species, each of which UV rays affect differently. Thus, organic glass is characterized by high throughput, which makes it possible to ensure the passage of the entire spectrum of solar radiation. The same applies to the quartz glass, which is used in lamps for solarium and in devices for disinfection of rooms. The usual glass used in residential premises and cars is transmitted exclusively long-wave rays of type A, and it is impossible to tan through it. Another thing, if you replace it with plexiglass. Then it will be possible to take sunbathing and enjoy the beautiful tan almost all year round.

Although sometimes there are cases when a person spends some time under the sunny rays passing through the window, and then detects light tan in open areas. Of course, he is in full confidence that he tanned precisely by insolation through the glass. But it is not so. There is a very simple explanation to this phenomenon: the change in the shade in this case occurs as a result of the activation of a small amount of residual, developed under the influence of the type ultraviolet in pigment (melanin) located in skin cells. As a rule, such a "tan" is temporary, that is, quickly disappears. In a word, in order to purchase a full tan, you need to either visit the solarium, or regularly take solar baths, and to achieve a change in the natural hue of the skin to the side of a darker through the usual window or automotive glass will not work.

Do you need to defend yourself?

Worried about whether it is possible to get a tan through glass, it is necessary only to those people who have very sensitive skin and predisposition to the emergence of pigment spots. They are recommended to constantly use special means with the minimum degree of protection (SPF). Apply such cosmetics should be mainly on the face, neck and zone. However, it is too much to protect against ultraviolet, all the more long-wave, still not worth it, because the sun's rays in moderate quantities are very useful and even necessary for the normal functioning of the human body.

As a child, I once asked Father: "Why does the glass misses the light?" By then, I learned that the light is a flow of particles, called photons, and it seemed to me awesome, as such a small particle can fly through thick glass. Father replied: "Because it is transparent." I was silent, since I understood that "transparent" there is only a synonym for expression "misses the light," and the father really does not know the answer. In school textbooks, there was also no answer, and I would like to know. Why is the glass misses the light?

Answer

The light of physics is not only visible light, but also invisible infrared radiation, ultraviolet radiation, X-rays, gamma radiation, radio waves. Materials transparent for one part of the spectrum (for example, for green light) can be non-transparent for other parts of the spectrum (red glass, for example, does not miss green rays). Conventional glass does not miss ultraviolet radiation, and quartz glass is transparent for ultraviolet. For X-rays, materials that do not miss visible light are transparent. Etc.

The light consists of particles called photons. Photons of different "color" (frequencies) carry different portions of energy.

Photons can be absorbed by the substance, transmitting energy and heating to it (well known to all who sunbathed on the beach). The light may be reflected from the substance, falling into our eyes, so we see the objects around them, and in full dark, where there are no light sources, we do not see anything. And the light can pass through the substance - and then we say that this substance is transparent.

Different materials in different proportions are absorbed, reflect and skip light and therefore differ in their optical properties (more dark and light, different colors, gloss, transparency): soot absorbs 95% of the light falling on it, and the polished silver mirror reflects 98% of light. Created material based on carbon nanotubes, which reflects only 45 thousandth percent of the incident light.

Questions arise: when the photon is absorbed by the substance when it is reflected and when it passes through the substance? We are now interested only in the third question, but in terms of us will answer the first.

The interaction of light and substance is the interaction of photons with electrons. The electron can absorb the photon and can emit a photon. There is no reflection of photons. The reflection of photons is called a two-stage process: the absorption of the photon and the subsequent radiation is exactly the same photon.

Electrons in the atom are able to occupy only certain orbits, each of which corresponds to their energy level. The atom of each chemical element is characterized by its set of energy levels, i.e, the permitted orbits of the electrons (the same refers to molecules, crystals condensed to the substance: in soot and diamond the same carbon atoms, but the optical properties of substances are different; metals, fine Reflective lights are transparent and even change the color (green gold), if there are thin film from them; amorphous glass does not miss ultraviolet, and from the same molecules of silicon oxide crystalline glass transparent for ultraviolet).

Absoring the photon of a certain energy (colors) electron goes to a higher orbit. On the contrary, by emptying the photon, the electron turns into a lower orbit. Electrons can absorb and emit not any photons, but only those whose energy (color) correspond to the difference in the energy levels of this atom.

Thus, as the light will behave when meeting with the substance (it will reflect, it will be swallowed, pass through) it depends on what is the allowed energy levels of this substance and what energy photons have (i.e. what color falling on the substance light).

So that the photon is absorbed by one of the electrons in the atom, it should have a strictly defined energy corresponding to the difference of energies of any two energy atoms, otherwise it flies past. In the glass, the distance between the individual energy levels is large, and no photon of visible light has an appropriate energy, which would have enough electron, absorbing the photon, could jump over to a higher energy level. Therefore, the glass skips the photons of visible light. But the photons of ultraviolet light have sufficient energy, so electrons absorb these photons and glass detains ultraviolet. In quartz glass, the distance between the permitted energy levels (energy slit) is even greater and therefore photons not only visible, but also ultraviolet light do not have enough energy so that the electrons can absorb them and go to the upper allowed levels.

So, the photons of visible light fly through the glass, because they do not have the corresponding energy for the transition of electrons to a higher energy level, and the glass is therefore seen transparent.

When adding impurities in the glass, having another energy spectrum, it can be made color - glass will absorb the photons of certain energies and skip the rest of the photons of visible light.

As is known, all bodies consist of molecules, and molecules - from atoms. Atoms are also not difficult (in our, the promotion description on the fingers). In the center of each atom there is a kernel consisting of a proton, or a group of protons and neutrons, and around, electrons are rotated in a circle on their electronic orbits / orbitals.

The light is also easy. Forget (who remembered) about the corpuscular-wave dualism and the Maxwell equation, let the light be a stream of photon balls, flying out of a flashlight directly to our eyes.

Now, if we put a concrete wall between a flashlight and eye - we will no longer see light. And if you delay a flashlight on this wall on our side - on the contrary, we will see, because the beam of light will affect the concrete, and will fall into our eyes. But through the concrete, the light will not go.

It is logical to assume that the photon balls are reflected and do not pass through the concrete wall because they are fighting about the atoms of the substance, i.e. concrete. It is more accurate about the electrons, for electrons rotate so quickly that the photon does not penetrate the electronic orbital to the kernel, and bounces and reflects already from the electron.

Why is the light pass through the glass wall? After all, inside the glass, too, molecules and atoms, and if you take a fairly thick glass, any photon should be encountered sooner or later, because the atoms are the same trillion in each grain grain! The thing is how the collisions of electrons with photons occur. We take the easiest case, one electron rotates around one proton (this is a hydrogen atom) and imagine that by this electron shook the photon.

All photon energy has passed the electron. It is said that the photon is absorbed by the electron and disappeared. And the electron received an additional energy (which was carried with him with himself) and from this additional energy he jumped to a higher orbit and began to fly further from the nucleus.

Most often, higher orbits are less stable, and after a while, the electron will empty this photon, i.e. "Let him go to freedom," and will return to his low stable orbit. The emitted photon will fly in a completely random side, then it will be absorbed by another, neighboring atom, and it will remain wander in the substance, until it is accidentally emitted back, or does not ultimately be on the heating of the concrete wall.

And now the most interesting. Electronic orbits cannot be anywhere around atom's core. Each atom of each chemical element has a clearly deterministic and final set of levels or orbits. The electron cannot be slightly climbed above or drop down slightly. It can only jump on a very clear gap of up or down, and since these levels differ in energies, which means that only a photon with a certain and very precisely specified energy can push the electron to a higher orbit.

It turns out that if we have three photons with different energies, and only one is exactly equal to the difference of energies between the levels of a particular atom, only this photon "collides" with the atom, the rest will fly by, in the literal sense "through the atom" For it will not be able to provide an electron clearly specified portion of energy to go to another level.

And how can we find photons with different energies?

It seems that the more speed, the higher the energy, everyone knows, but all the photons fly from the same speed - the speed of light!

Maybe the brighter and more powerful the source of the light (for example, if you take an army spotlight, instead of a flashlight), the more energy will be at the photons? Not. In the powerful and bright beam of the searchlight, just a greater number of photon pieces themselves, but the energy of each individual photon is exactly the same as in those that fly out of a dead pocket lantern.

And here we will still have to remember that the light is not only a flow of particles balls, but also a wave. Different photons differ in different wavelengths, i.e. Different frequency of own oscillations. And the higher the frequency of oscillations, the more powerful energy charge carries the photon.

Low-frequency photons (infrared light or radio wave) carry little energy, high-frequency (ultraviolet light or x-ray) - a lot. Visible light - somewhere in the middle. Here and lies the rays of the transparency of the glass! All the atoms in the glass have electrons in such orbits, which, to move to a higher energy, the impetus is needed, which is not enough in the photons of visible light. Therefore, it passes through the glass, practically not facing its atoms.

But ultraviolet photons are quite the energy needed to translate electrons with orbit into orbit, so in ultraviolet light, the usual window glass is completely black and opaque.

And what is interesting. Too much energy is also bad. The photon energy should be accuracy equal to the energy of the transition between orbits, from which any substance is transparent for one length (and frequencies) of electromagnetic waves, and not transparent to others, because all substances consist of different atoms and their configurations.

For example, concrete is transparent for radio waves, and infrared radiation, opaque for visible light and ultraviolet, is not transparent as well for X-ray, but is again transparent (to some extent) for gamma radiation.

That is why it is correct to say that glass is transparent for visible light. And for radio waves. And for gamma radiation. But opaque for ultraviolet. And almost not transparent for infrared light.

And if you still remember that the visible light is also not all white, but consists of different lengths (that is, the colors) waves from red to dark blue, it will become about it is clear why the items have different colors and shades, why red roses, and violets - blue.

Why are gases transparent, and there are no solids?

The temperature plays a decisive role in whether this substance will be solid, liquid or gaseous. Under normal pressure on the surface of the Earth at a temperature of 0 degrees Celsius and below the water is a solid. At temperatures between 0 and 100 degrees Celsius water - liquid. At temperatures above 100 degrees Celsius water - gas. Couples from the pan applies to the kitchen evenly in all directions. Based on the foregoing, suppose that through gases can be seen, and through solid bodies it is impossible. But some solids, such as glass, are just as transparent as air. How does it work? Most solids absorb the light falling on them. Part of the absorbed light energy goes to heating the body. Most of the incident light is reflected. Therefore, we see a solid, but we cannot see through it.

conclusions

The substance looks transparent when the quanta of light (photons) pass through it, without absorbing. But photons have different energy, and each chemical compound absorbs only those photons that have a suitable energy. On visible light - from red to violet - there is a very small range of photon energies. And just this range is "not interested" of silicon dioxide, the main component of the glass. Therefore, photons of visible light almost freely pass through the glass.

The question is not why the glass is transparent, but why other objects are not transparent. The whole thing in the energy levels on which electrons are located in the atom. You can imagine them in the form of various rows at the stadium. The electron has a certain place on one of the rows. However, if he has enough energy, it can jump over to another row. In some cases, the absorption of one of the photons passing through atom just ensures the necessary energy. But here snag. To transfer an electron from a number to a row, the photon must have a strictly defined amount of energy, otherwise it will fly by. So happens with glass. The rows are so far from each other that the energy of a photon of visible light is simply not enough to move the electrons between them.

And the photons of the ultraviolet energy spectrum grabs, so they are absorbed, and here, no matter how try, hiding behind the glass, do not contradict. In a century, which has passed since the production of glass, people completely appreciated its unique property to be simultaneously solid, and transparent. From windows, grubning daylight, and protecting from the elements, to devices that allow to look far into space, or observe microscopic worlds.

Having deprived modern glass civilization, and what will remain from it? Oddly enough, we rarely think about how important it is. Probably, it happens because, being transparent, the glass remains inconspicuous, and we forget about what it is.