Since ancient times, people have collected information about the world in which they live. There was only one science that combined all the information about nature that mankind had accumulated at that time. At that time, people did not know that they were observing examples of physical phenomena. At present, this science is called "natural science".

What does physical science study

Over time, scientific ideas about the world around us have noticeably changed - there are much more of them. Natural science has split into many separate sciences, including: biology, chemistry, astronomy, geography and others. In a number of these sciences, physics occupies not the last place. Discoveries and achievements in this area have allowed mankind to acquire new knowledge. These include the structure and behavior of various objects of all sizes (starting with giant stars and ending with the smallest particles - atoms and molecules).

The physical body is...

There is a special term "matter", which in the circles of scientists refers to everything that is around us. A physical body consisting of matter is any substance that occupies a certain place in space. Any physical body in action can be called an example of a physical phenomenon. Based on this definition, we can say that any object is a physical body. Examples physical bodies: button, notepad, chandelier, cornice, moon, boy, clouds.

What is a physical phenomenon

Any matter is in constant change. Some bodies are moving, others are in contact with the third, the fourth is spinning. No wonder many years ago the philosopher Heraclitus uttered the phrase "Everything flows, everything changes." Scientists even have a special term for such changes - these are all phenomena.

Everything that moves is a physical phenomenon.

What are the types of physical phenomena

• Thermal.

These are phenomena when, due to the influence of temperature, some bodies begin to transform (shape, size and state change). An example of physical phenomena: under the influence of the warm spring sun, icicles melt and turn into liquid, with the onset of cold weather, puddles freeze, boiling water becomes steam.

• Mechanical.

These phenomena characterize a change in the position of one body in relation to the rest. Examples: the clock is running, the ball is bouncing, the tree is swinging, the pen is writing, the water is flowing. All of them are in motion.

• Electrical.

The nature of these phenomena fully justifies its name. The word "electricity" is rooted in Greek language where "electron" means "amber". The example is quite simple and probably familiar to many. With a sharp removal of a woolen sweater, a small crack is heard. If you do this by turning off the light in the room, you can see the sparks.

• Light.

The body participating in the phenomenon, which is associated with light, is called luminous. As an example of physical phenomena, one can cite the well-known star of our solar system- The sun, as well as any other star, lamp, and even a firefly.

• Sound.

The propagation of sound, the behavior of sound waves in collisions with an obstacle, as well as other phenomena that are somehow related to sound, belong to this type of physical phenomena.

• Optical.

They happen because of the light. So, for example, man and animals are able to see because there is light. This group also includes the phenomena of propagation and refraction of light, its reflection from objects and its passage through different media.

Now you know what physical phenomena are. However, it should be understood that there is a certain difference between natural and physical phenomena. Yes, at natural phenomenon several physical phenomena occur simultaneously. For example, when lightning strikes the ground, the following phenomena occur: magnetic, sound, electrical, thermal and light.

We are surrounded by an infinitely diverse world of substances and phenomena.

It is constantly changing.

Any changes that occur to bodies are called phenomena. The birth of stars, the change of day and night, the melting of ice, the swelling of buds on trees, the flashing of lightning during a thunderstorm, and so on - all these are natural phenomena.

Recall that bodies are made up of substances. Note that in some phenomena the substances of bodies do not change, while in others they change. For example, if you tear a piece of paper in half, then, despite the changes that have occurred, the paper will remain paper. If the paper is burned, it will turn into ashes and smoke.

Phenomena in which may change the size, shape of bodies, the state of matter, but substances remain the same, do not change into others, are called physical phenomena(evaporation of water, the glow of an electric bulb, the sound of strings musical instrument etc.).

Physical phenomena are extremely diverse. Among them are distinguished mechanical, thermal, electrical, lighting and etc.

Let's remember how clouds float across the sky, an airplane flies, a car drives, an apple falls, a cart rolls, etc. In all of these phenomena, objects (bodies) move. Phenomena associated with a change in the position of a body in relation to other bodies are called mechanical(translated from the Greek "mechane" means machine, tool).

Many phenomena are caused by the change of heat and cold. In this case, the properties of the bodies themselves change. They change shape, size, the state of these bodies changes. For example, when heated, ice turns into water, water into steam; When the temperature drops, steam turns into water, water into ice. The phenomena associated with the heating and cooling of bodies are called thermal(Fig. 35).

Rice. 35. Physical phenomenon: the transition of matter from one state to another. If you freeze drops of water, ice will reappear

Consider electrical phenomena. The word "electricity" comes from the Greek word "electron" - amber. Remember that when you quickly take off your woolen sweater, you hear a slight crackle. If you do the same in complete darkness, you will also see sparks. This is the simplest electrical phenomenon.

To get acquainted with another electrical phenomenon, do the following experiment.

Tear off small pieces of paper and place them on the table surface. Comb clean and dry hair with a plastic comb and bring it to the pieces of paper. What happened?

Rice. 36. Small pieces of paper are attracted to the comb

Bodies that are capable of attracting light objects after rubbing are called electrified(Fig. 36). Lightning during thunderstorms, auroras, electrification of paper and synthetic fabrics - all these are electrical phenomena. The operation of the telephone, radio, television, various household appliances are examples of human use of electrical phenomena.

Phenomena that are associated with light are called light. Light comes from the sun, stars, lamps, and some living things, such as fireflies. Such bodies are called luminous.

We see when light hits the retina. We cannot see in absolute darkness. Objects that do not themselves emit light (for example, trees, grass, the pages of this book, etc.) are visible only when they receive light from some luminous body and reflect it from their surface.

The moon, which we often speak of as a night light, is in reality only a kind of reflector of sunlight.

By studying the physical phenomena of nature, a person has learned to use them in everyday life, everyday life.

1. What are called natural phenomena?

2. Read the text. List what natural phenomena are called in it: “Spring has come. The sun is getting hotter. Snow melts, streams run. Buds swelled on the trees, rooks flew in.

3. What phenomena are called physical?

4. From the physical phenomena listed below, write down the mechanical phenomena in the first column; in the second - thermal; in the third - electrical; in the fourth - light phenomena.

Physical phenomena: lightning flash; snow melting; coast; melting of metals; operation of an electric bell; rainbow in the sky; sunbeam; moving stones, sand with water; boiling water.

Ticket number 1

1. What does physics study. Some physical terms. Observations and experiments. Physical quantities. Measurement of physical quantities. Accuracy and error of measurements.

Physics is the science of the most general properties of bodies and phenomena.

How does a person know the world? How does he investigate the phenomena of nature, obtaining scientific knowledge about it?

The very first knowledge a person receives from observations behind nature.

To get the right knowledge, sometimes simple observation is not enough and you need to conduct experiment - a specially prepared experiment .

Experiments are carried out by scientists premeditated plan with a specific purpose .

During the experiments measurements are taken using special instruments of physical quantities. Examples physical quantities are: distance, volume, speed, temperature.

So, the source of physical knowledge is observations and experiments.

physical laws are based and verified on facts established by experience. Not less than important way knowledge - theoretical description of the phenomenon . Physical theories make it possible to explain known phenomena and predict new ones that have not yet been discovered.

Changes that occur with bodies are called physical phenomena.

Physical phenomena are divided into several types.

Types of physical phenomena:

1. Mechanical phenomena (for example, the movement of cars, aircraft, celestial bodies, fluid flow).

2. Electrical phenomena (for example, electricity, heating conductors with current, electrization of bodies).

3. Magnetic phenomena (for example, the effect of magnets on iron, the effect magnetic field Earth on the compass needle).

4. Optical phenomena (for example, the reflection of light from mirrors, the emission of light rays from various light sources).

5. Thermal phenomena (melting of ice, boiling of water, thermal expansion of bodies).

6. Atomic phenomena (for example, the operation of nuclear reactors, the decay of nuclei, processes occurring inside stars).

7. Sound phenomena (bell ringing, music, thunder, noise).

Physical terms are special words used in physics for brevity, definiteness and convenience.

Physical body is every object that surrounds us. (Display of physical bodies: pen, book, school desk)

Substance It is everything that physical bodies are made of. (Showing physical bodies consisting of different substances)

Matter is everything that exists in the universe regardless of our consciousness ( celestial bodies, plants, animals, etc.)

physical phenomena are changes that occur to physical bodies.

Physical quantities are the measurable properties of bodies or phenomena.

Physical Instruments- These are special devices that are designed to measure physical quantities and conduct experiments.

Physical quantities:
height h, mass m, path s, speed v, time t, temperature t, volume V, etc.

Units of measurement of physical quantities:

International system of units SI:

(international system)

Main:

Length - 1 m - (meter)

Time - 1 s - (second)

Weight - 1 kg - (kilogram)

Derivatives:

Volume - 1 m³ - (cubic meter)

Velocity - 1 m/s - (meter per second)

In this expression:

the number 10 is the numerical value of the time,

the letter "s" is an abbreviation for the unit of time (seconds),

and the combination of 10 s is the time value.

Prefixes to unit names:

To make it easier to measure physical quantities, in addition to the basic units, multiple units are used, which are in 10, 100, 1000, etc. more basic

g - hecto (×100) k - kilo (× 1000) M - mega (× 1000 000)

1 km (kilometer) 1 kg (kilogram)

1 km = 1000 m = 10³ m 1 kg = 1000 g = 10³ g

“Optical phenomena in nature”

1. Introduction

a) The concept of optics

b) Classification of optics

c) Optics in the development of modern physics

2. Phenomena associated with the reflection of light

4. Auroras

Introduction

The concept of optics

Very naive were the first ideas of ancient scientists about light. They thought that visual impressions arise when objects are felt with special thin tentacles that come out of the eyes. Optics was the science of vision, which is how the word can most accurately be translated.

Gradually, in the Middle Ages, optics turned from the science of vision into the science of light, facilitated by the invention of lenses and the camera obscura. At present, optics is a branch of physics that studies the emission of light and its propagation in various media, as well as its interaction with matter. Issues related to vision, the structure and functioning of the eye have emerged as a separate scientific area - physiological optics.

Optics classification

Light rays are geometric lines along which light energy propagates; when considering many optical phenomena, one can use the concept of them. In this case one speaks of geometric (ray) optics. Geometric optics is widely used in lighting engineering, as well as when considering the actions of numerous instruments and devices - from a magnifying glass and glasses to the most complex optical telescopes and microscopes.

Intensive studies of the previously discovered phenomena of interference, diffraction and polarization of light unfolded in early XIX century. These processes were not explained within the framework of geometric optics, so it was necessary to consider light in the form of transverse waves. As a result, wave optics appeared. Initially, it was believed that light is elastic waves in a certain medium (world ether) that fills the world space.

But the English physicist James Maxwell in 1864 created electromagnetic theory light, according to which the light waves are electromagnetic waves with the corresponding range of wavelengths.

And already at the beginning of the 20th century, new studies have shown that in order to explain some phenomena, such as the photoelectric effect, there is a need to present a light beam in the form of a stream of peculiar particles - light quanta. Isaac Newton had a similar point of view on the nature of light as early as 200 years ago in his "light emission theory". Quantum optics is doing this now.

The role of optics in the development of modern physics.

Optics also played a significant role in the development of modern physics. Optical research is associated in principle with the emergence of two of the most important and revolutionary theories of the twentieth century (quantum mechanics and the theory of relativity). Optical methods of substance analysis for molecular level gave rise to a special scientific direction - molecular optics, which also includes optical spectroscopy, which is used in modern materials science, in plasma studies, and in astrophysics. There are also electron and neutron optics.

On present stage development, an electron microscope and a neutron mirror were created, and optical models of atomic nuclei were developed.

Optics, influencing the development of various areas of modern physics, is itself in a period of rapid development today. The main impetus for this development was the invention of lasers - intense sources of coherent light. As a result, wave optics rose to a higher level, the level of coherent optics.

Thanks to the advent of lasers, a lot of scientific and technological developing areas have appeared. Among which are such as nonlinear optics, holography, radio optics, picosecond optics, adaptive optics, etc.

Radio optics originated at the intersection of radio engineering and optics and is engaged in the study of optical methods for transmitting and processing information. These methods are combined with traditional electronic methods; the result was a scientific and technical direction called optoelectronics.

The subject of fiber optics is the transmission of light signals through dielectric fibers. Using the achievements of nonlinear optics, it is possible to change the wavefront of a light beam, which is modified during the propagation of light in a particular medium, for example, in the atmosphere or in water. Consequently, adoptive optics has arisen and is being intensively developed. To which closely adjoins the photoenergetics that is emerging before our eyes, dealing, in particular, with the issues of efficient transmission of light energy along a beam of light. Modern laser technology makes it possible to obtain light pulses with a duration of the order of only a picosecond. Such pulses turn out to be a unique “tool” for studying a number of fast processes in matter, and in particular in biological structures. A special direction arose and is developing - picosecond optics; photobiology closely adjoins it. It can be said without exaggeration that the wide practical use of the achievements of modern optics is a prerequisite scientific and technological progress. Optics opened the way to the microcosm for the human mind, it also allowed him to penetrate the secrets star worlds. Optics covers all aspects of our practice.

Phenomena associated with the reflection of light.

The object and its reflection

The fact that the landscape reflected in stagnant water does not differ from the real one, but is only turned “upside down” is far from being the case.

If a person looks late in the evening at how the lamps are reflected in the water or how the shore descending to the water is reflected, then the reflection will seem shortened to him and will completely “disappear” if the observer is high above the surface of the water. Also, you can never see the reflection of the top of a stone, part of which is immersed in water.

The landscape is seen by the observer as if it were viewed from a point as much deeper than the surface of the water as the observer's eye is above the surface. The difference between the landscape and its image decreases as the eye approaches the surface of the water, as well as as the object moves away.

It often seems to people that the reflection of bushes and trees in a pond is distinguished by greater brightness of colors and saturation of tones. This feature can also be noticed by observing the reflection of objects in the mirror. Here plays a big role psychological perception than the physical side of the phenomenon. The frame of the mirror, the banks of the pond limit a small section of the landscape, protecting a person’s peripheral vision from excessive scattered light coming from the entire sky and blinding the observer, that is, he looks at a small section of the landscape as if through a dark narrow pipe. Reducing the brightness of reflected light compared to direct light makes it easier for people to see the sky, clouds, and other brightly lit objects that, when viewed directly, are too bright for the eye.

The dependence of the reflection coefficient on the angle of incidence of light.

At the boundary of two transparent media, light is partially reflected, partially passes into another medium and is refracted, partially absorbed by the medium. The ratio of the reflected energy to the incident energy is called the reflection coefficient. The ratio of the energy of light passing through a substance to the energy of incident light is called the transmittance.

The reflection and transmission coefficients depend on the optical properties, the media adjacent to each other, and the angle of incidence of the light. So, if light falls on a glass plate perpendicularly (angle of incidence α = 0), then only 5% of the light energy is reflected, and 95% passes through the interface. As the angle of incidence increases, the fraction of reflected energy increases. At the angle of incidence α=90˚ it is equal to one.

The dependence of the intensity of light reflected and passing through a glass plate can be traced by placing the plate at different angles to the light rays and estimating the intensity by eye.

It is also interesting to estimate by eye the intensity of light reflected from the surface of the reservoir, depending on the angle of incidence, to observe the reflection sun rays from the windows of the house at different angles of incidence during the day, at sunset, at sunrise.

Protective glasses

Ordinary window panes partially transmit heat rays. It is good for using them in northern areas as well as for greenhouses. In the south, the premises are so overheated that it is difficult to work in them. Protection from the sun comes down to either darkening the building with trees, or choosing a favorable orientation for the building when rebuilding. Both are sometimes difficult and not always feasible.

In order for the glass not to transmit heat rays, it is covered with thin transparent films of metal oxides. Thus, a tin-antimony film does not transmit more than half of the thermal rays, and coatings containing iron oxide completely reflect ultraviolet rays and 35-55% of thermal ones.

Solutions of film-forming salts are applied from a spray gun to a hot glass surface during its heat treatment or molding. At high temperatures, the salts turn into oxides, which are firmly bound to the glass surface.

Glasses for light-protective glasses are made in a similar way.

Complete internal reflection Sveta

A beautiful sight is a fountain, in which the ejected jets are illuminated from the inside. This can be depicted under normal conditions by doing the following experiment (Fig. 1). In a high tin can, at a height of 5 cm from the bottom, a round hole must be drilled ( A) with a diameter of 5-6 mm. An electric light bulb with a cartridge must be carefully wrapped with cellophane paper and placed opposite the hole. You need to pour water into the jar. Opening a hole A, we get a jet that will be illuminated from the inside. In a dark room, it glows brightly and looks very impressive. The jet can be given any color by placing colored glass in the path of the light rays. b. If you put your finger in the path of the jet, then the water is sprayed and these droplets glow brightly.

The explanation for this phenomenon is quite simple. A beam of light passes along a jet of water and hits a curved surface at an angle greater than the limit, experiences total internal reflection, and then again hits the opposite side of the jet at an angle again greater than the limit. So the beam passes along the jet, bending along with it.

But if the light were completely reflected inside the jet, then it would not be visible from the outside. Part of the light is scattered by water, air bubbles and various impurities present in it, as well as due to the uneven surface of the jet, so it is visible from the outside.

Cylindrical light guide

If you direct a light beam at one end of a solid curved glass cylinder, you can see that the light will come out of its other end (Fig. 2); through side surface cylinder light almost does not come out. The passage of light through a glass cylinder is explained by the fact that, falling on the inner surface of the cylinder at an angle greater than the limit, the light repeatedly undergoes total reflection and reaches the end.

The thinner the cylinder, the more often the beam will be reflected and the greater part of the light will fall on the inner surface of the cylinder at angles greater than the limit.

Diamonds and Gems

There is an exhibition of Russia's diamond fund in the Kremlin.

The lights in the hall are slightly dimmed. Jewelers' creations sparkle in the shop windows. Here you can see such diamonds as “Orlov”, “Shah”, “Maria”, “Valentina Tereshkova”.

The secret of the beautiful play of light in diamonds lies in the fact that this stone has a high refractive index (n=2.4173) and, as a result, a small angle of total internal reflection (α=24˚30′) and has a greater dispersion, causing the decomposition of white light for simple colors.

In addition, the play of light in a diamond depends on the correctness of its cut. The facets of a diamond repeatedly reflect light within the crystal. Due to the high transparency of high-class diamonds, the light inside them almost does not lose its energy, but only decomposes into simple colors, the rays of which then break out in various, most unexpected directions. When the stone is turned, the colors emanating from the stone change, and it seems that the stone itself is the source of many bright multi-colored rays.

There are diamonds painted in red, bluish and lilac colors. The brilliance of a diamond depends on its cut. When viewed through a well-cut water-clear diamond in the light, the stone appears completely opaque, and some of its facets look just black. This is because the light, undergoing total internal reflection, exits in the opposite direction or to the sides.

When you look at the top cut from the side of the world, it shines in many colors, and in places it glitters. The bright sparkle of the upper facets of a diamond is called diamond brilliance. The underside of the diamond from the outside seems to be silver-plated and casts with a metallic sheen.

The most transparent and large diamonds serve as decoration. Small diamonds are found wide application in engineering as a cutting or grinding tool for machine tools. Diamonds are used to reinforce the heads of drilling tools for drilling wells in hard rocks. This use of diamond is possible because of the great hardness that distinguishes it. Other gemstones in most cases are aluminum oxide crystals with an admixture of oxides of coloring elements - chromium (ruby), copper (emerald), manganese (amethyst). They are also hard, durable and have a beautiful color and “play of light”. At present, they are able to artificially obtain large crystals of aluminum oxide and paint them in the desired color.

The phenomena of light dispersion are explained by the variety of colors of nature. A whole complex of optical experiments with prisms in the 17th century was carried out by the English scientist Isaac Newton. These experiments showed that white light is not the main one, it must be considered as a composite (“non-uniform”); the main ones are different colors (“homogeneous” rays, or “monochromatic” rays). The decomposition of white light into different colors occurs for the reason that each color has its own degree of refraction. These conclusions made by Newton are consistent with modern scientific ideas.

Along with the dispersion of the refractive index, there is a dispersion of the coefficients of absorption, transmission, and reflection of light. This explains the various effects in the illumination of bodies. For example, if there is some body transparent to light, in which the transmittance is large for red light, and the reflection coefficient is small, for green light it is the other way around: the transmittance is small, and the reflectance is large, then in transmitted light the body will appear red, and green in reflected light. Such properties are possessed, for example, by chlorophyll, a green substance contained in the leaves of plants and causing green color. A solution of chlorophyll in alcohol when viewed through the light is red. In reflected light, the same solution appears green.

If some body has a large absorption coefficient, and the transmission and reflection coefficients are small, then such a body will appear black and opaque (for example, soot). A very white, opaque body (such as magnesium oxide) has a reflectance close to unity for all wavelengths, and very low transmittance and absorption. A body (glass) that is completely transparent to light has low reflection and absorption coefficients and a transmittance close to unity for all wavelengths. For colored glass, for some wavelengths, the transmittance and reflection coefficients are practically equal to zero and, accordingly, the value of the absorption coefficient for the same wavelengths is close to unity.

Phenomena associated with the refraction of light

Some types of mirages. From a larger variety of mirages, we single out several types: “lake” mirages, also called inferior mirages, superior mirages, double and triple mirages, ultra-long-range vision mirages.

Inferior ("lake") mirages arise over a strongly heated surface. Superior mirages, on the contrary, occur over a strongly cooled surface, for example, over cold water. If the lower mirages are observed, as a rule, in deserts and steppes, then the upper ones are observed in northern latitudes.

Superior mirages are diverse. In some cases they give a direct image, in other cases an inverted image appears in the air. Mirages can be double when two images are observed, a simple one and an inverted one. These images may be separated by a strip of air (one may be above the horizon, the other below it), but may directly merge with each other. Sometimes there is another - the third image.

Especially amazing are the mirages of ultra-long vision. K. Flammarion in his book “Atmosphere” describes an example of such a mirage: “Based on the testimony of several trustworthy persons, I can report a mirage that was seen in the city of Verviers (Belgium) in June 1815. One morning, the inhabitants of the city saw in the sky army, and so clearly that one could distinguish the suits of artillerymen and even, for example, a cannon with a broken wheel, which is about to fall off ... It was the morning of the Battle of Waterloo!” The described mirage is depicted in the form of a colored watercolor by one of the eyewitnesses. The distance from Waterloo to Verviers in a straight line is more than 100 km. There are cases when such mirages were observed at large distances - up to 1000 km. The “Flying Dutchman” should be attributed precisely to such mirages.

Explanation of the lower (“lake”) mirage. If the air at the very surface of the earth is very hot and, therefore, its density is relatively low, then the refractive index at the surface will be less than in higher air layers. Changing the refractive index of air n with height h near earth's surface for the case under consideration is shown in Figure 3, a.

In accordance with the established rule, light rays near the surface of the earth will in this case be bent so that their trajectory is convex downward. Let an observer be at point A. Light beam from some area blue sky hits the eye of the observer, experiencing the specified curvature. And this means that the observer will see the corresponding section of the sky not above the horizon line, but below it. It will seem to him that he sees water, although in fact he has an image of a blue sky in front of him. If we imagine that there are hills, palm trees or other objects near the horizon, then the observer will see them upside down due to the marked curvature of the rays, and will perceive them as reflections of the corresponding objects in non-existent water. This is how an illusion appears, which is a “lake” mirage.

Simple superior mirages. It can be assumed that the air at the very surface of the earth or water is not heated, but, on the contrary, noticeably cooled compared to higher air layers; the change in n with height h is shown in Figure 4, a. Light rays in the case under consideration are bent so that their trajectory is convex upwards. Therefore, now the observer can see objects hidden from him beyond the horizon, and he will see them above, as if hanging above the horizon line. Therefore, such mirages are called superior.

An superior mirage can produce both upright and inverted images. The direct image shown in the figure occurs when the refractive index of air decreases relatively slowly with height. With a rapid decrease in the refractive index, an inverted image is formed. This can be verified by considering a hypothetical case - the refractive index at a certain height h decreases abruptly (Fig. 5). The rays of the object, before reaching the observer A, experience total internal reflection from the boundary BC, below which, in this case, there is denser air. It can be seen that the superior mirage gives an inverted image of the object. In reality, there is no jump-like boundary between the layers of air, the transition takes place gradually. But if it is done sharply enough, then the superior mirage will give an inverted image (Fig. 5).

Double and triple mirages. If the refractive index of air changes first rapidly and then slowly, then the rays in region I will be bent faster than in region II. As a result, two images appear (Fig. 6, 7). The light rays 1 propagating within the air region I form an inverted image of the object. Beams 2, which propagate mainly within region II, are curved to a lesser extent and form a straight image.

To understand how a triple mirage appears, one must imagine three successive air regions: the first (near the surface itself), where the refractive index decreases slowly with height, the next, where the refractive index decreases rapidly, and the third region, where the refractive index decreases slowly again. The figure shows the considered change in the refractive index with height. The figure shows how a triple mirage occurs. Rays 1 form the lower image of the object, they propagate within the air region I. Rays 2 form an inverted image; I fall into the air region II, these rays experience a strong curvature. Beams 3 form the upper direct image of the object.

Mirage of ultra-long vision. The nature of these mirages is the least studied. It is clear that the atmosphere must be transparent, free from water vapor and pollution. But this is not enough. A stable layer of cooled air should form at some height above the ground. Below and above this layer, the air should be warmer. A light beam that has fallen inside a dense cold layer of air is, as it were, “locked” inside it and propagates in it like a kind of light guide. The ray trajectory in Figure 8 is convex all the time towards the less dense regions of the air.

The emergence of ultra-distant mirages can be explained by the propagation of rays inside such “light guides”, which are sometimes created by nature.

The rainbow is a beautiful celestial phenomenon that has always attracted the attention of man. In the old days, when people still knew little about the world around them, the rainbow was considered a “heavenly sign”. So, the ancient Greeks thought that the rainbow is the smile of the goddess Irida.

The rainbow is observed in the direction opposite to the Sun, against the background of rain clouds or rain. A multi-colored arc is usually located at a distance of 1-2 km from the observer, and sometimes it can be observed at a distance of 2-3 m against the background of water drops formed by fountains or water sprays.

The center of the rainbow is on the continuation of the straight line connecting the Sun and the eye of the observer - on the anti-solar line. The angle between the direction to the main rainbow and the antisolar line is 41-42º (Fig. 9).

At the time of sunrise, the antisolar point (point M) is on the horizon line and the rainbow looks like a semicircle. As the sun rises, the antisolar point falls below the horizon and the size of the rainbow decreases. It is only part of a circle.

Often there is a secondary rainbow, concentric with the first, with an angular radius of about 52º and an inverse arrangement of colors.

At a Sun height of 41º, the main rainbow ceases to be visible and only a part of the secondary rainbow appears above the horizon, and at a Sun height of more than 52º, the secondary rainbow is not visible either. Therefore, in the middle equatorial latitudes, this natural phenomenon is never observed during the near noon hours.

The rainbow has seven primary colors that smoothly transition from one to another.

The shape of the arc, the brightness of the colors, the width of the stripes depend on the size of the water droplets and their number. Large drops create a narrower rainbow, with sharply prominent colors, small drops create an arc that is blurry, faded and even white. That is why a bright narrow rainbow is visible in the summer after a thunderstorm, during which large drops fall.

The rainbow theory was first given in 1637 by René Descartes. He explained the rainbow as a phenomenon associated with the reflection and refraction of light in raindrops.

The formation of colors and their sequence were explained later, after unraveling the complex nature of white light and its dispersion in the medium. The diffraction theory of the rainbow was developed by Airy and Partner.

We can consider the simplest case: let a beam of parallel solar rays fall on drops having the shape of a ball (Fig. 10). A beam incident on the surface of a drop at point A is refracted inside it according to the law of refraction:

n sin α=n sin β, where n=1, n≈1.33 –

respectively, the refractive indices of air and water, α is the angle of incidence, and β is the angle of refraction of light.

Inside the drop, the ray AB goes in a straight line. At point B, the beam is partially refracted and partially reflected. It should be noted that the smaller the angle of incidence at point B, and hence at point A, the lower the intensity of the reflected beam and the greater the intensity of the refracted beam.

Beam AB after reflection at point B occurs at an angle β`=β b hits point C, where partial reflection and partial refraction of light also occur. The refracted beam leaves the drop at an angle γ, and the reflected one can go further, to point D, etc. Thus, the light beam in the drop undergoes multiple reflection and refraction. With each reflection, some of the rays of light come out and their intensity inside the drop decreases. The most intense of the rays emerging into the air is the ray that emerged from the drop at point B. But it is difficult to observe it, since it is lost against the background of bright direct sunlight. The rays refracted at point C, together, create a primary rainbow against the background of a dark cloud, and rays refracted at point D give a secondary rainbow, which is less intense than the primary one.

When considering the formation of a rainbow, one more phenomenon must be taken into account - the unequal refraction of light waves of different lengths, that is, light rays different color. This phenomenon is called dispersion. Due to dispersion, the angles of refraction γ and the angle of deflection of rays Θ in a drop are different for rays of different colors.

Most often we see one rainbow. It is not uncommon for two rainbow stripes to appear simultaneously in the sky, located one after the other; watching and more more celestial arcs - three, four and even five at the same time. This interesting phenomenon Leningraders observed on September 24, 1948, when four rainbows appeared among the clouds over the Neva in the afternoon. It turns out that a rainbow can arise not only from direct rays; often it appears in the reflected rays of the sun. This can be seen on the coast of sea bays, large rivers and lakes. Three or four rainbows - ordinary and reflected - sometimes create a beautiful picture. Since reflected from water surface the rays of the Sun go from bottom to top, then the rainbow formed in the rays can sometimes look completely unusual.

You should not think that a rainbow can be observed only during the day. It happens at night, however, always weak. You can see such a rainbow after a night rain, when the moon looks out from behind the clouds.

Some semblance of a rainbow can be obtained from this experiment: You need to illuminate a flask filled with water with sunlight or a lamp through a hole in the white board. Then a rainbow will become clearly visible on the board, and the angle of divergence of the rays compared to the initial direction will be about 41-42 °. Under natural conditions, there is no screen, the image appears on the retina of the eye, and the eye projects this image onto the clouds.

If a rainbow appears in the evening before sunset, then a red rainbow is observed. In the last five or ten minutes before sunset, all the colors of the rainbow, except for red, disappear, it becomes very bright and visible even ten minutes after sunset.

A beautiful sight is a rainbow on the dew. It can be observed at sunrise on the grass covered with dew. This rainbow is shaped like a hyperbola.

auroras

One of the most beautiful optical phenomena of nature is the aurora borealis.

In most cases, auroras are green or blue-green in color, with occasional patches or borders of pink or red.

Auroras are observed in two main forms - in the form of ribbons and in the form of cloud-like spots. When the radiance is intense, it takes on the form of ribbons. Losing intensity, it turns into spots. However, many ribbons disappear before they break into spots. The ribbons seem to hang in the dark space of the sky, resembling a giant curtain or drapery, usually stretching from east to west for thousands of kilometers. The height of this curtain is several hundred kilometers, the thickness does not exceed several hundred meters, and it is so delicate and transparent that stars can be seen through it. The lower edge of the curtain is quite sharply and distinctly outlined and often tinted in red or pinkish color, reminiscent of the border of the curtain, the upper one is gradually lost in height and this creates a particularly spectacular impression of the depth of space.

There are four types of auroras:

Homogeneous arc - the luminous strip has the simplest, calmest form. It is brighter from below and gradually disappears upward against the background of the glow of the sky;

Radiant arc - the tape becomes somewhat more active and mobile, it forms small folds and streams;

Radiant band - with increasing activity, larger folds are superimposed on small ones;

With increased activity, the folds or loops expand to enormous sizes, the lower edge of the ribbon shines brightly with a pink glow. When the activity subsides, the wrinkles disappear and the tape returns to a uniform shape. This suggests that the uniform structure is the main form of the aurora, and the folds are associated with an increase in activity.

Often there are aurora of a different kind. They capture the entire polar region and are very intense. They occur during an increase solar activity. These lights appear as a whitish-green cap. Such auroras are called squalls.

According to the brightness of the aurora, they are divided into four classes, differing from each other by one order of magnitude (that is, 10 times). The first class includes aurora, barely noticeable and approximately equal in brightness Milky Way, the radiance of the fourth class illuminates the Earth as brightly as the full moon.

It should be noted that the aurora that has arisen propagates to the west at a speed of 1 km/sec. The upper layers of the atmosphere in the area of ​​auroral flashes are warmed up and rush upwards, which affected the enhanced deceleration artificial satellites Land passing these zones.

During auroras, eddy electric currents arise in the Earth's atmosphere, capturing large areas. They excite magnetic storms, the so-called additional unstable magnetic fields. When the atmosphere shines, it radiates X-rays, which are most likely the result of deceleration of electrons in the atmosphere.

Frequent flashes of radiance are almost always accompanied by sounds resembling noise, crackling. The aurora borealis has a great influence on strong changes in the ionosphere, which in turn affects the conditions of radio communication, i.e., radio communication deteriorates greatly, resulting in strong interference, or even complete loss of reception.

The emergence of polar lights.

The earth is a huge magnet, the north pole of which is near the south geographic pole, and the southern one is close to the northern one. And the lines of force of the Earth's magnetic field are geomagnetic lines coming out of the area adjacent to the north magnetic pole of the Earth. They cover the entire globe and enter it in the area of ​​the south magnetic pole, forming a toroidal lattice around the Earth.

It was believed for a long period of time that the location of the magnetic field lines is symmetrical with respect to earth's axis. But in fact, it turned out that the so-called “solar wind,” i.e., the flow of protons and electrons emitted by the Sun, hits the geomagnetic shell of the Earth from a height of about 20,000 km. It pulls it away from the Sun, thereby forming a kind of magnetic “tail” near the Earth.

Once in the Earth's magnetic field, an electron or a proton moves in a spiral, winding around the geomagnetic line. These particles, which fell from the solar wind into the Earth's magnetic field, are divided into two parts: one part along the magnetic field lines immediately flows into the polar regions of the Earth, and the other part gets inside the teroid and moves inside it, as is possible according to the left hand rule, along closed curve ABC. In the end, these protons and electrons also flow along geomagnetic lines to the region of the poles, where their increased concentration appears. Protons and electrons produce ionization and excitation of atoms and molecules of gases. To do this, they have sufficient energy. Since protons arrive at the Earth with energies of 10000-20000 eV (1 eV = 1.6 10 j), and electrons with energies of 10-20 eV. And for the ionization of atoms, it is necessary: ​​for hydrogen - 13.56 eV, for oxygen - 13.56 eV, for nitrogen - 124.47 eV, and even less for excitation.

By the principle of how it happens in tubes with a rarefied gas, when currents are passed through them, the excited gas atoms give back the received energy in the form of light.

The green and red glow, according to the results of the spectral study, belongs to excited oxygen atoms, and the infrared and violet glow belong to ionized nitrogen molecules. Some emission lines of oxygen and nitrogen are formed at an altitude of 110 km, and the red glow of oxygen is formed at an altitude of 200-400 km. The next weak source of red light is hydrogen atoms, formed in the upper atmosphere from protons that arrived from the Sun. Such a proton, after capturing an electron, turns into an excited hydrogen atom and emits red light.

After flares on the Sun, aurora flares usually occur in a day or two. This indicates a connection between these phenomena. A study using rockets showed that in places of greater intensity of auroras, more high level ionization of gases by electrons. According to scientists, the maximum intensity of auroras is achieved off the coast of oceans and seas.

There are a number of difficulties in scientifically explaining all the phenomena associated with the auroras. That is, the mechanism of acceleration of particles to certain energies is not completely known, their trajectories of movement in near-Earth space are not clear, the mechanism for the formation of luminescence is not entirely clear. various kinds, the origin of sounds is unclear, not everything converges quantitatively in the energy balance of ionization and excitation of particles.

Used Books:

1. “Physics in nature”, author - L. V. Tarasov, publishing house “Prosveshchenie”, Moscow, 1988.
2. “Optical phenomena in nature”, author - V. L. Bulat, publishing house “Prosveshchenie”, Moscow, 1974.
3. “Conversations on Physics, Part II”, author - M.I. Bludov, Prosveshchenie publishing house, Moscow, 1985.
4. "Physics 10", authors - G. Ya. Myakishev B. B. Bukhovtsev, publishing house "Prosveshchenie", Moscow, 1987.
5. “Encyclopedic dictionary of a young physicist”, compiled by V. A. Chuyanov, publishing house “Pedagogy”, Moscow, 1984.
6. “Schoolchildren's Handbook of Physics”, compiled by the Philological Society “Slovo”, Moscow, 1995.
7. “Physics 11”, N. M. Shakhmaev, S. N. Shakhmaev, D. Sh. Shodiev, Prosveshchenie publishing house, Moscow, 1991.
8. “Solution of problems in physics”, V. A. Shevtsov, Nizhne-Volzhsky book publishing house, Volgograd, 1999.

Everything that surrounds us: both animate and inanimate nature, is in constant motion and is constantly changing: planets and stars move, it rains, trees grow. And a person, as we know from biology, constantly goes through some stages of development. Grinding grains into flour, falling stone, boiling water, lightning, glowing light bulbs, dissolving sugar in tea, movement Vehicle, lightning, rainbows are examples of physical phenomena.

And with substances (iron, water, air, salt, etc.) various changes or phenomena occur. The substance can be crystallized, melted, crushed, dissolved and again separated from the solution. However, its composition will remain the same.

So, granulated sugar can be ground into a powder so fine that at the slightest breath it will rise into the air like dust. Sugar specks can only be seen under a microscope. Sugar can be divided into even smaller parts by dissolving it in water. If water is evaporated from the sugar solution, the sugar molecules will again combine with each other into crystals. But when dissolved in water, and when crushed, sugar remains sugar.

In nature, water forms rivers and seas, clouds and glaciers. During evaporation, water turns into steam. Water vapor is water in the gaseous state. When exposed to low temperatures (below 0˚С), water turns into a solid state - it turns into ice. The smallest particle of water is a water molecule. The water molecule is also the smallest particle of steam or ice. Water, ice and steam are not different substances, but the same substance (water) in different states of aggregation.

Like water, other substances can be transferred from one state of aggregation into another.

Characterizing one or another substance as a gas, liquid or solid, they mean the state of the substance under normal conditions. Any metal can not only be melted (translated into a liquid state), but also turned into a gas. But this requires very high temperatures. In the outer shell of the Sun, metals are in a gaseous state, because the temperature there is 6000 ° C. And, for example, carbon dioxide by cooling it can be turned into "dry ice".

Phenomena in which there is no transformation of one substance into another are referred to as physical phenomena. Physical phenomena can lead to a change, for example, in the state of aggregation or temperature, but the composition of substances will remain the same.

All physical phenomena can be divided into several groups.

Mechanical phenomena are phenomena that occur with physical bodies when they move relative to each other (the revolution of the Earth around the Sun, the movement of cars, the flight of a parachutist).

Electrical phenomena are phenomena that arise from the appearance, existence, movement and interaction electric charges(electric current, telegraphy, lightning during a thunderstorm).

Magnetic phenomena are phenomena associated with the appearance of physical bodies magnetic properties(magnet attraction of iron objects, turning the compass needle to the north).

Optical phenomena are phenomena that occur during the propagation, refraction and reflection of light (rainbow, mirages, reflection of light from a mirror, the appearance of a shadow).

Thermal phenomena are phenomena that occur when physical bodies are heated and cooled (melting snow, boiling water, fog, freezing water).

Atomic phenomena are phenomena that occur when there is a change internal structure substances of physical bodies (glow of the Sun and stars, atomic explosion).

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