Dynamic change is built into nature itself. Everything changes one way or another every moment. If you look around carefully, you will find hundreds of examples of physical and chemical phenomena that are quite natural transformations.
Change is the only constant in the universe
Ironically, change is the only constant in our universe. To understand physical and chemical phenomena (examples in nature are found at every step), it is customary to classify them according to types, depending on the nature of the end result caused by them. Distinguish between physical, chemical and mixed changes, which contain both the first and the second.
Physical and chemical phenomena: examples and meaning
What is a physical phenomenon? Any changes that occur in a substance without changing its chemical composition are physical. They are characterized by changes in physical attributes and material state (solid, liquid or gaseous), density, temperature, volume, which occur without changing its fundamental chemical structure. There is no creation of new chemical products or a change in the total mass. Moreover, this type of change is usually temporary and in some cases completely reversible.
When you mix chemicals in the laboratory, it is easy to see the reaction, but there are many chemical reactions going on in the world around you every day. A chemical reaction changes molecules, while a physical change only rearranges them. For example, if we take chlorine gas and sodium metal and combine them, we get table salt. The resulting substance is very different from any of its constituent parts. It's a chemical reaction. If we then dissolve this salt in water, we simply mix the salt molecules with the water molecules. There is no change in these particles, it is a physical transformation.
Examples of physical changes
Everything is made of atoms. When atoms join together, different molecules are formed. The different properties that objects inherit are the result of different molecular or atomic structures. The main properties of an object depend on their molecular location. Physical changes occur without changing the molecular or atomic structure of objects. They simply transform the state of the object without changing its nature. Melting, condensation, volume change and evaporation are examples of physical phenomena.
Additional examples of physical changes: metal expanding when heated, sound transmission through air, water freezing into ice in winter, copper is drawn into wires, clay forming on different objects, ice cream melts to liquid, metal heating and transforming it into another form, iodine sublimation when heating, falling of any object by gravity, ink absorbed by chalk, magnetization of iron nails, snowman melting in the sun, glowing incandescent bulbs, magnetic levitation of an object.
How to distinguish between physical and chemical changes?
Many examples of chemical and physical phenomena can be found in life. It is often difficult to tell the difference between the two, especially when both can happen at the same time. To identify physical changes, ask the following questions:
- Is the state of the state of an object a change (gaseous, solid, and liquid)?
- Is the change a purely limited physical parameter or characteristic such as density, shape, temperature, or volume?
- Is the chemical nature of the object a change?
- Do chemical reactions occur that lead to the creation of new products?
If the answer to one of the first two questions is yes, and there are no answers to the following questions, it is most likely a physical phenomenon. Conversely, if the answer to either of the last two questions is yes, while the first two are negative, it is definitely a chemical phenomenon. The trick is to just clearly observe and analyze what you see.
Examples of chemical reactions in everyday life
Chemistry takes place in the world around you, not just in the laboratory. Matter interacts to form new products through a process called chemical reaction or chemical change. Every time you cook or clean, this is chemistry at work. Your body lives and grows through chemical reactions. There are reactions when you take medication, light a match, and sigh. Here are 10 chemical reactions in everyday life. This is just a small selection of the physical and chemical phenomena in life that you see and experience many times every day:
- Photosynthesis. Chlorophyll in plant leaves converts carbon dioxide and water into glucose and oxygen. This is one of the most common daily chemical reactions, and also one of the most important because this is how plants produce food for themselves and animals and convert carbon dioxide into oxygen.
- Aerobic cellular respiration is a reaction with oxygen in human cells. Aerobic cellular respiration is the opposite process of photosynthesis. The difference is that energy molecules combine with the oxygen we breathe to release the energy our cells need, as well as carbon dioxide and water. The energy used by cells is chemical energy in the form of ATP.
- Anaerobic breathing. Anaerobic respiration produces wine and other fermented foods. Your muscle cells perform anaerobic respiration when you deplete your oxygen supply, such as during intense or prolonged exercise. Anaerobic respiration by yeast and bacteria is used for fermentation to produce ethanol, carbon dioxide, and other chemicals that make cheese, wine, beer, yogurt, bread, and many other common foods.
- Combustion is a type of chemical reaction. This is a chemical reaction in everyday life. Every time you light a match or candle, light a fire, you see the combustion reaction. Combustion combines energy molecules with oxygen to produce carbon dioxide and water.
- Rust is a common chemical reaction. Over time, the iron develops a red, flaky coating called rust. This is an example of an oxidation reaction. Other everyday examples include copper verdigers and silver tarnishing.
- Mixing chemicals causes chemical reactions. Baking powder and baking soda perform similar functions in baking, but they react differently to other ingredients, so you can't always replace them with another. If you combine vinegar and baking soda for chemical "volcano" or milk with baking powder in a recipe, you are experiencing a double-shift or metathesis reaction (plus a few others). The ingredients are recombined to produce carbon dioxide gas and water. Carbon dioxide forms bubbles and helps "grow" baked goods. These reactions seem simple in practice, but often involve several steps.
- Batteries are examples of electrochemistry. Batteries use electrochemical or redox reactions to convert chemical energy into electrical energy.
- Digestion. Thousands of chemical reactions take place during digestion. Once you put food in your mouth, an enzyme in your saliva called amylase begins to break down sugars and other carbohydrates into simpler forms that your body can absorb. The hydrochloric acid in your stomach reacts with food to break it down, and enzymes break down proteins and fats so they can be absorbed into the bloodstream through the intestinal wall.
- Acid-base reactions. Whenever you mix an acid (eg vinegar, lemon juice, sulfuric acid, hydrochloric acid) with an alkali (eg baking soda, soap, ammonia, acetone), you are performing an acid-base reaction. These processes neutralize each other, producing salt and water. Sodium chloride is not the only salt that can be formed. For example, here is the chemical equation for an acid-base reaction that produces potassium chloride, a common table salt substitute: HCl + KOH → KCl + H 2 O.
- Soap and detergents. They are purified by chemical reactions. Soap emulsifies dirt, which means oil stains bind to the soap so they can be removed with water. Detergents reduce the surface tension of the water, so they can interact with oils, isolate them and rinse them out.
- Chemical reactions during cooking. Cooking is one great practical experiment in chemistry. Cooking uses heat to induce chemical changes in food. For example, when you boil an egg vigorously, the hydrogen sulfide produced by heating the egg white can react with the iron from the egg yolk, forming a gray-green ring around the yolk. When you cook meats or baked goods, the Maillard reaction between amino acids and sugars gives the brown color and the desired flavor.
Other examples of chemical and physical phenomena
Physical properties describe characteristics that do not change a substance. For example, you can change the color of the paper, but it is still paper. You can boil water, but when you collect and condense steam, it is still water. You can determine the mass of a sheet of paper and it is still paper.
Chemical properties are those that indicate how a substance reacts or does not react with other substances. When sodium metal is placed in water, it reacts violently to form sodium hydroxide and hydrogen. Sufficient heat is generated by the hydrogen bursting into flames by reacting with the oxygen in the air. On the other hand, when you put a piece of copper metal in water, there is no reaction. Thus, the chemical property of sodium is that it reacts with water, while the chemical property of copper is that it does not.
What other examples of chemical and physical phenomena can be cited? Chemical reactions always take place between electrons in the valence shells of the atoms of the elements in the periodic table. Physical phenomena at low energy levels simply involve mechanical interactions - random collisions of atoms without chemical reactions such as atoms or gas molecules. When the collision energies are very high, the integrity of the atomic nucleus is disrupted, resulting in the fission or fusion of the species involved. Spontaneous radioactive decay is usually considered a physical phenomenon.
About the world around. Apart from the usual curiosity, this was due to practical needs. After all, for example, if you know how to raise
and move heavy stones, you can build strong walls and build a house that is more comfortable to live in than in a cave or dugout. And if you learn to smelt metals from ores and make plows, scythes, axes, weapons, etc., you will be able to plow the field better and get a higher yield, and in case of danger you will be able to protect your land.
In ancient times, there was only one the science- she combined all the knowledge about nature that mankind had accumulated by that time. Today this science is called natural science.
Learning about physical science
Light is another example of an electromagnetic field. You will learn about some of the properties of light in Section 3.
3. Remembering physical phenomena
The matter around us is constantly changing. Some bodies move relative to each other, some of them collide and, possibly, collapse, others are formed from some bodies ... The list of such changes can be continued and continued - it is not for nothing that in ancient times the philosopher Heraclitus remarked: "Everything flows, everything changes." Changes in the world around us, that is, in nature, scientists call special term- phenomena.
Rice. 1.5. Examples of natural phenomena
Rice. 1.6. A complex natural phenomenon - a thunderstorm can be represented as a combination of a number of physical phenomena
Sunrise and sunset, avalanche, volcanic eruption, horse running, panther jump - all these are examples of natural phenomena (Fig. 1.5).
To better understand complex natural phenomena, scientists divide them into a set of physical phenomena - phenomena that can be described using physical laws.
In fig. 1.6 shows a set of physical phenomena that form a complex natural phenomenon - a thunderstorm. So, lightning - a huge electrical discharge - is an electromagnetic phenomenon. If lightning strikes a tree, then it flares up and begins to generate heat - physics in this case, they speak of a thermal phenomenon. The rumble of thunder and the crackle of a burning tree are sound phenomena.
Examples of some physical phenomena are given in the table. Take a look, for example, at the first row of the table. What can be in common between the flight of a rocket, the fall of a stone and the rotation of an entire planet? The answer is simple. All examples of phenomena given in this line are described by the same laws - the laws of mechanical motion. Using these laws, you can calculate the coordinates of any moving body (be it a stone, a rocket or a planet) at any moment of time of interest to us.
Rice. 1.7 Examples of electromagnetic phenomena
Each of you, taking off your sweater or combing your hair with a plastic comb, probably paid attention to the tiny sparks that appear at the same time. Both these sparks and the mighty lightning discharge refer to the same electromagnetic phenomena and, accordingly, obey the same laws. Therefore, to study electromagnetic phenomena, one should not wait for a thunderstorm. It is enough to study how safe sparks behave in order to understand what to expect from lightning and how to avoid possible danger. For the first time such studies were carried out by the American scientist B. Franklin (1706-1790), who invented an effective means of protection against a lightning discharge - a lightning rod.
Having studied physical phenomena separately, scientists establish their relationship. Thus, a lightning discharge (electromagnetic phenomenon) is necessarily accompanied by a significant increase in temperature in the lightning channel (thermal phenomenon). The study of these phenomena in their interrelation has made it possible not only to better understand the natural phenomenon - a thunderstorm, but also to find a way of practical application of electromagnetic and thermal phenomena. Surely each of you, passing by the construction site, saw workers in protective masks and dazzling flashes of electric welding. Electric welding (a method of joining metal parts using an electric discharge) is an example of the practical use of scientific research.
4. Determine what physics studies
Now that you have learned what matter and physical phenomena are, it's time to determine what is the subject of physics study. This science studies: the structure and properties of matter; physical phenomena and their relationship.
- summing up
The world around us is made of matter. There are two types of matter: the substance of which all physical bodies are composed, and the field.
The world that surrounds us is constantly changing. These changes are called phenomena. Thermal, light, mechanical, sound, electromagnetic phenomena are all examples of physical phenomena.
The subject of physics study is the structure and properties of matter, physical phenomena and their relationship.
- Control questions
What does physics study? Give examples of physical phenomena. Can events that occur in a dream or in the imagination be considered physical phenomena? 4. What substances do the following bodies consist of: textbook, pencil, soccer ball, glass, car? What physical bodies can be made of glass, metal, wood, plastic?
Physics. Grade 7: Textbook / F. Ya. Bozhinova, N. M. Kiryukhin, E. A. Kiryukhina. - X .: Ranok Publishing House, 2007. - 192 p .: ill.
Lesson content lesson outline and support frame lesson presentation interactive technologies accelerative teaching methods Practice tests, online testing tasks and exercises homework workshops and trainings questions for class discussions Illustrations video and audio materials photos, pictures, graphics, tables, diagrams comics, parables, sayings, crosswords, anecdotes, jokes, quotes Add-onsSince 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. Physics is not the last in a number of these sciences. 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 flux. 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"
- Introduction
- Light reflection phenomena
a) The concept of optics
b) Classification of optics
c) Optics in the development of modern physics
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 this 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 magnifying glasses 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 a corresponding range of lengths.
And already at the beginning of the XX century, new studies have shown 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 gave 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 to him shortened 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 passing 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 of sunlight 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 performing 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 jet, 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 a light beam into one end of a solid curved glass cylinder, you can see that light will come out of 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 multicolored 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 in many colors, and in 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 precious stones in most cases 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, when viewed through the light, turns out to be red. 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, on the other hand, appear 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 bend in this case so that their trajectory is curved downward. Let an observer be at point A. A ray of light from a certain area of the blue sky enters 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, due 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 the case under consideration, 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 over 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 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 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 bent 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 as if along 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 on the side opposite 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 is no longer 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 drops 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 one can pass further, to point D, etc. Thus, the light ray in the drop undergoes multiple reflection and refraction. With each reflection, some of the light rays go 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 a 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 auroras 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 that are barely noticeable and approximately equal in brightness to the Milky Way, while the fourth class 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 affected the intensified deceleration of artificial Earth satellites passing through these zones.
During the aurora, eddy electric currents arise in the Earth's atmosphere, covering 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 arrangement 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. He 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. The study with the help of rockets showed that in places of higher intensity of aurora, a higher level of ionization of gases by electrons is maintained. 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 completely known, their trajectories in near-earth space are not clear, the mechanism of the formation of various types of luminescence is not completely clear, the origin of sounds is unclear, not everything converges quantitatively in the energy balance of ionization and excitation of particles.
Used Books:
- "Physics in nature", author - L. V. Tarasov, publishing house "Education", Moscow, 1988.
- "Optical phenomena in nature", author - VL Bulat, publishing house "Prosveshchenie", Moscow, 1974.
- “Conversations on Physics, Part II”, author - MI Bludov, Publishing House “Prosveshchenie”, Moscow, 1985.
- "Physics 10", authors - G. Ya. Myakishev BB Bukhovtsev, publishing house "Education", Moscow, 1987.
- "Encyclopedic Dictionary of a Young Physicist", compiled by V. A. Chuyanov, publishing house "Pedagogy", Moscow, 1984.
- "Schoolchild's Handbook on Physics", compiled by the Philological Society "Slovo", Moscow, 1995.
- "Physics 11", N. M. Shakhmaev, S. N. Shakhmaev, D. Sh. Shodiev, publishing house "Education", Moscow, 1991.
- “Solving problems in physics”, V. A. Shevtsov, Nizhne-Volzhsky book publishing house, Volgograd, 1999.