All physical phenomena in physics. Examples of physical phenomena and their description. The physical body is

Man lives in the natural world. You yourself and everything that surrounds you - air, trees, river, sun - these are different objects of nature... The objects of nature are constantly undergoing changes, which are called natural phenomena.
Since ancient times, people have tried to understand: how and why do various phenomena occur? How do birds fly and why do they not fall? How can a tree float on water and why doesn't it sink? Some natural phenomena - thunder and lightning, solar and lunar eclipses - frightened people until scientists figured out how and why they occur.
Observing and studying the phenomena occurring in nature, people have found their application in their lives. Observing the flight of birds (Fig. 1), people constructed an airplane (Fig. 2).

Rice. 1	Rice. 2

Observing a floating tree, man learned to build ships, conquered the seas and oceans. Having studied the method of movement of the jellyfish (Fig. 3), scientists came up with rocket engine(fig. 4). By observing lightning, scientists discovered electricity, without which people today cannot live and work. All kinds of household electrical devices (lighting lamps, televisions, vacuum cleaners) surround us everywhere. Various electrical tools (electric drill, electric saw, sewing machine) are used in school workshops and in production.

Scientists have divided all physical phenomena into groups (Fig. 6):

Rice. 6

Mechanical phenomena are phenomena that occur with physical bodies when they move relative to each other (revolution of the Earth around the Sun, movement of cars, swing of a pendulum).
Electrical phenomena- These are the phenomena that arise when electric charges appear, exist, move and interact (electric current, lightning).
Magnetic phenomena - these are phenomena associated with the appearance of magnetic properties in physical bodies (the attraction of iron objects by a magnet, the rotation of the compass needle to the north).
Optical phenomena- these are phenomena that occur during the propagation, refraction and reflection of light (reflection of light from a mirror, mirages, the appearance of a shadow).
Thermal phenomena- these are the phenomena associated with the heating and cooling of physical bodies (boiling of a kettle, the formation of fog, the transformation of water into ice).
Atomic phenomena- these are phenomena that arise when the internal structure of the substance of physical bodies changes (glow of the Sun and stars, atomic explosion).
Observe and explain. 1. Give an example of a natural phenomenon. 2. What group of physical phenomena does it belong to? Why? 3. Name the physical bodies that participated in physical phenomena.

Ticket number 1

1. What physics studies. 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 natural phenomena, gaining scientific knowledge about him?

A person gets the very first knowledge from observations for nature.

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

Experiments are carried out by scientists a pre-planned plan with a specific purpose .

During experiments measurements are taken with the help of special devices for physical quantities. Examples physical quantities are: distance, volume, speed, temperature.

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

Physical laws are based and verified on empirically established facts. An equally important way of knowing is theoretical description of the phenomenon . Physical theories allow one to explain known phenomena and predict new ones that have not yet been discovered.

The changes that take place in 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, airplanes, celestial bodies, fluid flow).

2. Electrical phenomena (for example, electric current, heating of conductors with current, electrification of bodies).

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

4. Optical phenomena (for example, reflection of light from mirrors, 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 atomic reactors, the decay of nuclei, the processes taking place inside the 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 around us. (Showing physical bodies: pen, book, desk)

Substance is all that the physical bodies are made of. (Showing physical bodies consisting of different substances)

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

Physical phenomena- these are changes taking place with physical bodies.

Physical quantities are measurable properties of bodies or phenomena.

Physical devices- 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)

Basic:

Length - 1 m - (meter)

Time - 1 s - (second)

Weight - 1 kg - (kilogram)

Derivatives:

Volume - 1 m³ - (cubic meter)

Speed ​​- 1 m / s - (meter per second)

In this expression:

number 10 - numerical value of time,

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

and the combination of 10 s is the time value.

Unit names prefixes:

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

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

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

What physical science studies

Over time, scientific ideas about the world around them have changed markedly - 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 does not occupy the last place. Discoveries and achievements in this area have allowed humanity to possess new knowledge. These include the structure and behavior of various objects of all sizes (from giant stars to the smallest particles - atoms and molecules).

The physical body is ...

There is a special term "matter", which in the circles of scientists is called 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 of physical bodies: button, notebook, chandelier, cornice, moon, boy, clouds.

What is a physical phenomenon

Any matter is in constant change. Some bodies move, others touch the third, the fourth rotate. It is not for nothing that 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.

Physical phenomena include everything that moves.

What are the types of physical phenomena

• Thermal.

These are phenomena when, due to the effect 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, the puddles freeze, boiling water becomes vapor.

• 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 jumping, the tree is swinging, the pen is writing, the water is flowing. They are all in motion.

• Electrical.

The nature of these phenomena fully justifies its name. The word "electricity" is rooted in the Greek language, where "electron" means "amber". The example is quite simple and probably familiar to many. When you take off your woolen sweater abruptly, you hear a slight crackling sound. If you do this by turning off the light in the room, then you can see sparks.

• Light.

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

• Sound.

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

• Optical.

They are due to 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 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. Thus, in a natural phenomenon, several physical phenomena occur simultaneously. For example, when lightning strikes the ground, the following sound, electrical, heat and light occur.

"Optical phenomena in nature"

1. Introduction

a) The concept of optics

b) Classification of optics

c) Optics in the development of modern physics

2. Light reflection phenomena

4. Aurora Borealis

Introduction

Optics concept

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

Gradually, in the Middle Ages, optics from the science of vision turned into the science of light, the invention of lenses and a pinhole camera contributed to this. At the present time, 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 became widespread 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 began at the beginning of the 19th century. These processes were not explained in terms 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 world space.

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

And already at the beginning of the 20th century, new studies carried out showed that to explain some phenomena, for example, 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 200 years ago in his "theory of the outflow of light." Now quantum optics is doing this.

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 for analyzing matter at the molecular level have given rise to a special scientific field - molecular optics, which also includes optical spectroscopy, which is used in modern materials science, in plasma research, in astrophysics. There are also electronic and neutron optics.

At the present stage of development, an electron microscope and a neutron mirror have been created, and optical models of atomic nuclei have been developed.

Optics, influencing the development of various areas of modern physics, and itself today is in a period of rapid development. 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 technical developing directions have appeared. Among which are such as nonlinear optics, holography, radio optics, picosecond optics, adaptive optics, etc.

Radio optics originated at the junction 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. Applying the achievements of nonlinear optics, it is possible to change the wavefront of a light beam, which is modified when light propagates in a particular medium, for example, in the atmosphere or in water. Consequently, adoptive optics arose and is intensively developing. To which is closely adjacent to the emerging before our eyes photoenergy, which deals, in particular, with the issues of effective transmission of light energy through a beam of light. Modern laser technology makes it possible to obtain light pulses with a duration of only a picosecond. Such impulses turn out to be a unique “tool” for studying a whole range of fast processes in matter, and in particular in biological structures. A special direction has arisen and is developing - picosecond optics; photobiology is closely related to it. It can be said without exaggeration that the widespread practical use of the achievements of modern optics is a prerequisite for scientific and technological progress. Optics opened the way to the microcosm for the human mind, it also allowed him to penetrate the secrets of the stellar worlds. Optics covers all aspects of our practice.

Phenomena associated with the reflection of light.

The subject and its reflection

The fact that the landscape reflected in the stagnant water does not differ from the real one, but is only turned upside down is far from 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 completely “disappear” if the observer is high above the surface of the water. Also, you can never see the reflection of the top of the stone, part of which is submerged in water.

The landscape is seen by the observer as if they were looking at it from a point located 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 a greater brightness of colors and saturation of tones. This feature can also be noticed by observing the reflection of objects in the mirror. Here psychological perception plays a greater role than the physical side of the phenomenon. The frame of the mirror, the banks of the pond limit a small area of ​​the landscape, protecting the person's peripheral vision from excess scattered light coming from the entire sky and a blinding observer, that is, he looks at a small area 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 border of two transparent media, light is partially reflected, partially passed into another medium and 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 transmitted through a substance to the energy of incident light is called the transmittance.

Reflection and transmission coefficients depend on the optical properties of the adjoining media and the angle of incidence of 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 an angle of incidence α = 90˚, it is equal to one.

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

It is also interesting to evaluate 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 allow heat rays to pass through. This is good for northern areas as well as greenhouses. In the south, the premises are so overheated that it is difficult to work in them. Sun protection comes down to either darkening the building with trees, or choosing a favorable orientation for the building during rebuilding. Both are sometimes difficult and not always feasible.

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

Solutions of film-forming salts are applied from a spray gun onto a hot glass surface during heat treatment or shaping. At high temperatures, salts transform into oxides, which are tightly bound to the glass surface.

Likewise, lenses for light-protective glasses are made.

Total internal light reflection

A beautiful sight is the 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). Drill a round hole in a tall tin can at a height of 5 cm from the bottom ( a) with a diameter of 5-6 mm. The light bulb with the socket must be carefully wrapped in cellophane paper and placed in front of the hole. You need to pour water into the jar. Opening the hole a, we get a stream 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 stream, then the water is sprayed and these droplets glow brightly.

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

But if the light was 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 irregularities in the surface of the jet, therefore it is visible from the outside.

Cylindrical light guide

If you direct the light beam into one end of a solid curved glass cylinder, you will notice that the light will come out from its other end (Fig. 2); almost no light escapes through the lateral surface of the cylinder. The passage of light through the glass cylinder is explained by the fact that, falling on the inner surface of the cylinder at an angle greater than the limiting one, the light repeatedly experiences full reflection and reaches the end.

The thinner the cylinder, the more often reflections of the beam will occur and the greater part of the light will fall on the inner surface of the cylinder at angles greater than the limiting one.

Diamonds and Gems

There is an exhibition of the Russian diamond fund in the Kremlin.

The light in the hall is slightly dim. The jewelers' creations sparkle in the windows. Here you can see such diamonds as "Orlov", "Shah", "Maria", "Valentina Tereshkova".

The secret of the charming 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 into simple colors.

In addition, the play of light in a diamond depends on the correct cut. The facets of a diamond reflect light multiple times 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 burst out in various, most unexpected directions. When the stone is turned, the colors emanating from the stone change, and it seems that it itself is the source of many bright multi-colored rays.

There are diamonds colored in red, bluish and lilac colors. The brilliance of a diamond depends on its cut. If you look through a well-cut water-transparent diamond into light, the stone appears completely opaque, and some of its edges look just black. This is because the light, undergoing total internal reflection, comes out in the opposite direction or to the sides.

If you look at the upper cut from the cardinal direction, it shines with many colors, and in some places glitters. The bright sparkle of the upper facets of a diamond is called diamond sparkle. The underside of the diamond from the outside seems to be silvered and casts a metallic sheen.

The most transparent and large diamonds serve as decoration. Small diamonds are widely used in technology as cutting or grinding tools for metalworking machines. Diamonds are used to reinforce the heads of drilling tools for drilling wells in hard rocks. This application of diamond is possible due to its great distinguishing hardness. Other gems in most cases, they are crystals of aluminum oxide 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". Currently, they are able to artificially obtain large crystals of aluminum oxide and paint them in the desired color.

The phenomenon of light dispersion is 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 should be considered as composite (“inhomogeneous”); the main ones are different colors (“uniform” 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, the dispersion of the absorption, transmission and reflection coefficients of light is observed. This explains the various effects when lighting bodies. For example, if there is some body transparent to light, for which the transmittance is large for red light, and the reflection coefficient is small, for green light, on the contrary: the transmittance is small, and the reflection coefficient 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 plant leaves and causing green color... A solution of chlorophyll in alcohol turns out to be red when viewed in light. In reflected light, the same solution looks green.

If some body has a high absorption coefficient, but the transmittance and reflection coefficients are small, then such a body will appear black and opaque (for example, soot). A very white, opaque body (for example, magnesium oxide) has a reflectance close to unity for all wavelengths, and very low transmittance and absorption coefficients. A body (glass) that is completely transparent to light has low reflection and absorption coefficients and a transmission coefficient close to unity for all wavelengths. For colored glass, for some wavelengths, the transmittance and reflection coefficients are practically 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. Of the larger variety of mirages, we can single out several types: “lake” mirages, also called lower mirages, upper mirages, double and triple mirages, ultra-long-range vision mirages.

Lower (“lake”) mirages appear over a highly heated surface. Upper mirages appear, on the contrary, 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.

The upper mirages are diverse. In some cases they give an upright 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 can be separated by a strip of air (one can be above the horizon line, the other below it), but they can directly close with each other. Sometimes another image appears - a third image.

The mirages of ultra-long-range vision are especially amazing. K. Flammarion in his book “Atmosphere” describes an example of such a mirage: “Based on the testimonies of several trustworthy persons, I can report on 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 the army, and it was so clear that it was possible to discern the costumes of the gunners and even, for example, a cannon with a broken wheel, which was about to fall off ... It was the morning of the battle at Waterloo! ” The described mirage is depicted in color 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. Air refractive index change n with height h near the 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 bend so that their trajectory is curved downward. Let an observer be at point A. Light beam from a certain area blue sky falls into the eye of the observer, experiencing the indicated curvature. 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 in front of him is an image of a blue sky. If we imagine that there are hills, palms or other objects near the horizon, then the observer will see them upside down, thanks to the marked bending of the rays, and perceive them as reflections of the corresponding objects in non-existent water. This is how an illusion arises, which is a “lake” mirage.

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

The superior mirage can give both a direct and an inverted image. The live image shown in the figure occurs when the refractive index of air decreases relatively slowly with height. When the refractive index decreases rapidly, an inverted image is formed. This can be verified by considering the 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 upper mirage gives an inverted image of the object. In reality, there is no abrupt boundary between the layers of air, the transition occurs gradually. But if it is done abruptly enough, then the upper mirage will give an inverted image (Fig. 5).

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

To understand how a triple mirage appears, you need to imagine three successive air regions: the first (near the surface), 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 the triple mirage arises. Beams 1 form the bottom image of the object, they propagate within the air region I. Beams 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-range vision. The nature of these mirages is the least studied. It is clear that the atmosphere should be transparent, free from water vapor and pollution. But this is not enough. A stable layer of cooled air should form at a certain height above the ground. Below and above this layer, the air should be warmer. A ray of light that has fallen into a dense cold layer of air is, as it were, "locked" inside it and spreads in it like a kind of light guide. The ray trajectory in Figure 8 is always convex towards the less dense regions of the air.

The emergence of ultra-long-range mirages can be explained by the propagation of rays inside such “light guides” that nature sometimes creates.

A rainbow is a beautiful celestial phenomenon - it has always attracted the attention of a person. 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 Iris.

A rainbow is observed in the opposite direction to the Sun, against a 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 droplets formed by fountains or water sprays.

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

At the moment of sunrise, the anti-sun point (point M) is on the horizon and the rainbow looks like a semicircle. As the Sun rises, the anti-sun point drops below the horizon and the size of the rainbow decreases. It represents only part of a circle.

A collateral rainbow is often observed, concentric with the first, with an angular radius of about 52º and reversed colors.

When the Sun's height is 41º, the main rainbow ceases to be visible and only a part of the subsidiary rainbow protrudes above the horizon, and when the Sun is more than 52º, the subsidiary rainbow is not visible either. Therefore, in mid-equatorial latitudes in the midday hours, this natural phenomenon is never observed.

The rainbow has seven primary colors, smoothly passing one into the other.

The type of 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 distinguished colors, small ones create a blurry, faded and even white arc. This 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 solving the complex nature of white light and its dispersion in the medium. The rainbow diffraction theory was developed by Erie and Partner.

We can consider the simplest case: let a beam of parallel sun rays fall on the drops having the shape of a ball (Fig. 10). A ray falling 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.

Beam AB goes in a straight line inside the drop. At point B, the ray is partially refracted and partially reflected. It should be noted that the smaller the angle of incidence at point B, and therefore 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 and hits point C, where partial reflection and partial refraction of light also occurs. The refracted ray leaves the drop at an angle γ, while the reflected ray can pass further, to point D, etc. Thus, the light ray in the drop undergoes multiple reflection and refraction. With each reflection, some part of the light rays goes out and their intensity decreases inside the droplet. The most intense of the rays that go out into the air is the ray that came out of the drop at point B. But it is difficult to observe it, since it is lost against the background of bright direct sunlight. On the other hand, the rays refracted at point C together create a primary rainbow against the background of a dark cloud, and rays refracted at point D produce 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 of different colors. This phenomenon is called dispersion. Due to dispersion, the angles of refraction γ and the angle of deflection of the rays Θ in the droplet are different for rays of different colors.

Most often we see one rainbow. There are frequent cases when two rainbow stripes appear simultaneously in the firmament, located one after the other; an even greater number of celestial arcs are observed - three, four and even five at the same time. This interesting phenomenon was observed by Leningraders 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; quite often it appears in the reflected rays of the sun. This can be seen on the shores of sea bays, large rivers and lakes. Three or four rainbows - ordinary and reflected - sometimes create beautiful picture... Since the rays of the Sun reflected from the water surface go from bottom to top, the rainbow formed in the rays can sometimes look completely unusual.

One should not think that a rainbow can only be observed during the day. It happens at night, but it is 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 experience: 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 in comparison with 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 colors of the rainbow except red disappear, it becomes very bright and visible even ten minutes after sunset.

A beautiful sight is the rainbow on the dew. It can be observed at sunrise on the dew-covered grass. This rainbow has a hyperbole shape.

Polar lights

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

In most cases, auroras are green or blue-green with occasional spots or a pink or red border.

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 tapes 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, its thickness does not exceed several hundred meters, and it is so delicate and transparent that the stars are visible through it. The lower edge of the curtain is quite sharply and distinctly outlined and is often tinted red or pinkish, reminiscent of the border of the curtain, the upper edge is gradually lost in height and this creates a particularly effective impression of the depth of space.

There are four types of auroras:

Homogeneous arc - the luminous strip has the simplest, quietest shape. 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 trickles;

Radiant stripe - with an increase in activity, larger folds are superimposed on small ones;

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

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

In terms of brightness, auroras are divided into four classes, differing from each other by one order of magnitude (that is, 10 times). The first class includes auroras, barely noticeable and approximately equal in brightness The milky way while the fourth-class aurora illuminates the Earth as brightly as the full moon.

It should be noted that the resulting aurora spreads westward at a speed of 1 km / sec. The upper layers of the atmosphere in the area of ​​auroral flares are warming up and rushing upward, which has affected the intensified deceleration of artificial Earth satellites passing through these zones.

During the auroras, vortexes appear in the Earth's atmosphere. electric currents capturing large areas. They excite magnetic storms, the so-called additional unstable magnetic fields. When the atmosphere is glowing, it emits X-rays, which are most likely the result of the braking of electrons in the atmosphere.

Frequent flashes of aurora are almost always accompanied by sounds resembling noise, crackling. Auroras have a great influence on strong changes in the ionosphere, which in turn affect the conditions of radio communication, i.e. radio communication is greatly deteriorated, resulting in strong interference, or even complete loss of reception.

The emergence of aurora borealis.

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

It was believed for a long period of time that the location of the magnetic lines of force was symmetrical about the earth's axis. But in fact, it turned out that the so-called "solar wind", that is, the flux of protons and electrons emitted by the Sun, hits the geomagnetic shell of the Earth from an altitude of about 20,000 km. It pulls it away from the Sun, thereby forming a kind of magnetic "tail" at the Earth.

Trapped in the Earth's magnetic field, an electron or a proton moves in a spiral, winding on the geomagnetic line. These particles, caught 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 falls inside the theroid and moves inside it, as is possible according to the left-hand rule, along closed curve ABC. Eventually, these protons and electrons along geomagnetic lines also flow down to the region of the poles, where their increased concentration appears. Protons and electrons produce ionization and excitation of atoms and molecules of gases. For 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, for excitation it is even less.

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

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

After solar flares, auroral flares usually occur in a day or two. This indicates a connection between these phenomena. A rocket study showed that in areas of higher auroral intensity, more high level ionization of gases by electrons. According to scientists, the maximum intensity of the auroras is achieved near the shores of the oceans and seas.

There are a number of difficulties in the scientific explanation of all the phenomena associated with aurora borealis. That is, the mechanism of acceleration of particles to certain energies is not fully known, their trajectories in near-Earth space are not clear, the mechanism of the formation of glow is not entirely clear. different types, 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 "Education", Moscow, 1988.
2. "Optical phenomena in nature", author - VL Bulat, publishing house "Prosveshchenie", Moscow, 1974.
3. “Conversations on Physics, Part II”, author - MI Bludov, Publishing House “Prosveshchenie”, Moscow, 1985.
4. "Physics 10", authors - G. Ya. Myakishev BB Bukhovtsev, publishing house "Education", Moscow, 1987.
5. "Encyclopedic Dictionary of a Young Physicist", compiled by V. A. Chuyanov, publishing house "Pedagogy", Moscow, 1984.
6. “Schoolchild's Handbook on Physics”, compiled by the Philological Society “Slovo”, Moscow, 1995.
7. "Physics 11", N. M. Shakhmaev, S. N. Shakhmaev, D. Sh. Shodiev, publishing house "Education", Moscow, 1991.
8. “Solving problems in physics”, V. A. Shevtsov, Nizhne-Volzhsky book publishing house, Volgograd, 1999.

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 the trees, the flashing of lightning during a thunderstorm, and so on - all these are natural phenomena.

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

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

Physical phenomena are extremely varied. Among them there are mechanical, thermal, electrical, light and etc.

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

Many phenomena are caused by changes in heat and cold. In this case, changes in the properties of the bodies themselves occur. 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 a substance from one state to another. If you freeze water droplets, ice will reappear

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

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

Pick up small pieces of paper and place them on the table top. Comb through clean, dry hair with a plastic comb and bring it up to the pieces of paper. What happened?

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

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

The phenomena that are associated with light are called light. Light is emitted by the Sun, stars, lamps and some living things, such as firefly beetles. Such bodies are called luminous.

We see under the condition of exposure to light on the retina of the eye. We cannot see in absolute darkness. Objects that do not emit light themselves (for example, trees, grass, 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 talk about as a night light, is in reality only a kind of reflector of sunlight.

Studying the physical phenomena of nature, man 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 warmer. The snow is melting, streams are running. The 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 - electric; in the fourth, light phenomena.

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