Interesting experiments about the refraction of light. Features of the phenomenon of light refraction from the point of view of physics. Phenomenon in life
The Greek astronomer Claudius Ptolemy (circa 130 AD) is the author of a remarkable book that served as the main textbook on astronomy for almost 15 centuries. However, in addition to the astronomical textbook, Ptolemy also wrote the book Optics, in which he outlined the theory of vision, the theory of flat and spherical mirrors, and the study of the phenomenon of light refraction. Ptolemy encountered the phenomenon of light refraction while observing the stars. He noticed that a beam of light, passing from one medium to another, "breaks". Therefore, a stellar ray, passing through the earth's atmosphere, reaches the surface of the earth not in a straight line, but along a curved line, that is, refraction occurs. The curvature of the beam path occurs due to the fact that the air density changes with height.
To study the law of refraction, Ptolemy conducted the following experiment. He took the circle and fixed the rulers l1 and l2 on the axis so that they could freely rotate around it (see figure). Ptolemy immersed this circle in water up to the diameter AB and, turning the lower ruler, ensured that the rulers lay for the eye on one straight line (if you look along the upper ruler). After that, he took the circle out of the water and compared the angles of incidence α and refraction β. He measured angles with an accuracy of 0.5°. The numbers obtained by Ptolemy are presented in the table.
Ptolemy did not find a "formula" of the relationship for these two series of numbers. However, if you determine the sines of these angles, it turns out that the ratio of the sines is expressed by almost the same number, even with such a rough measurement of the angles that Ptolemy resorted to.
Due to the refraction of light in a calm atmosphere, the apparent position of the stars in the sky relative to the horizon
1) above actual position
2) below actual position
3) shifted in one direction or another vertically relative to the actual position
4) matches the actual position
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In a calm atmosphere, the positions of stars that are not perpendicular to the surface of the Earth at the point where the observer is located are observed. What is the apparent position of the stars - above or below their actual position relative to the horizon? Explain the answer.
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Refraction in the text refers to the phenomenon
1) changes in the direction of propagation of a light beam due to reflection at the boundary of the atmosphere
2) changes in the direction of propagation of a light beam due to refraction in the Earth's atmosphere
3) absorption of light as it propagates through the earth's atmosphere
4) light beam bending around obstacles and thus deflecting rectilinear propagation
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Which of the following conclusions contradicts Ptolemy's experiments?
1) the angle of refraction is less than the angle of incidence when the beam passes from air to water
2) as the angle of incidence increases, the angle of refraction increases linearly
3) the ratio of the sine of the angle of incidence to the sine of the angle of refraction does not change
4) the sine of the angle of refraction depends linearly on the sine of the angle of incidence
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Photoluminescence
Some substances, when illuminated by electromagnetic radiation, begin to glow themselves. This glow, or luminescence, has an important feature: the luminescence light has a different spectral composition than the light that caused the glow. Observations show that luminescence light has a longer wavelength than the exciting light. For example, if a beam of violet light is directed to a cone with a solution of fluorescein, then the illuminated liquid begins to luminesce brightly with green-yellow light.
Some bodies retain the ability to glow for some time after their illumination has ceased. Such an afterglow can have a different duration: from fractions of a second to many hours. It is customary to call a glow that stops with lighting, fluorescence, and a glow that has a noticeable duration, phosphorescence.
Phosphorescent crystalline powders are used to coat special screens that remain luminous for two to three minutes after illumination. Such screens also glow under the action of X-rays.
Phosphorescent powders have found a very important application in the manufacture of fluorescent lamps. In gas-discharge lamps filled with mercury vapor, when an electric current passes, ultraviolet radiation is produced. Soviet physicist S.I. Vavilov proposed to cover the inner surface of such lamps with a specially made phosphorescent composition, which, when irradiated with ultraviolet, gives visible light. By selecting the composition of the phosphorescent substance, it is possible to obtain the spectral composition of the emitted light, as close as possible to the spectral composition of daylight.
The phenomenon of luminescence is characterized by extremely high sensitivity: sometimes 10 - - 10 g of a luminous substance, for example, in solution, is enough to detect this substance by its characteristic glow. This property is the basis of luminescent analysis, which makes it possible to detect negligible impurities and to judge about impurities or processes that lead to a change in the original substance.
Human tissues contain a wide variety of natural fluorophores, which have different fluorescence spectral regions. The figure shows the emission spectra of the main fluorophores of biological tissues and the scale of electromagnetic waves.
According to the given data, pyroxidine glows
1) red light
2) yellow light
3) green light
4) purple light
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Two identical crystals, having the property of phosphorescence in the yellow part of the spectrum, were preliminarily illuminated: the first with red rays, the second with blue rays. For which of the crystals will it be possible to observe an afterglow? Explain the answer.
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When examining food products, the luminescent method can be used to detect spoilage and falsification of products.
The table shows the indicators of the luminescence of fats.
Butter luminescence color changed from yellow-green to blue. This means that the butter could have added
1) only butter margarine
2) only margarine "Extra"
3) only vegetable fat
4) any of the specified fats
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Earth Albedo
The temperature at the Earth's surface depends on the reflectivity of the planet - albedo. Surface albedo is the ratio of the energy flux of reflected sunlight to the energy flux of solar rays incident on the surface, expressed as a percentage or fraction of a unit. The Earth's albedo in the visible part of the spectrum is about 40%. In the absence of clouds, it would be about 15%.
Albedo depends on many factors: the presence and condition of cloudiness, changes in glaciers, seasons, and, accordingly, on precipitation.
In the 90s of the XX century, the significant role of aerosols - "clouds" of the smallest solid and liquid particles in the atmosphere became obvious. When fuel is burned, gaseous oxides of sulfur and nitrogen enter the air; combining in the atmosphere with water droplets, they form sulfuric, nitric acids and ammonia, which then turn into sulfate and nitrate aerosols. Aerosols not only reflect sunlight without letting it through to the Earth's surface. Aerosol particles serve as nuclei for the condensation of atmospheric moisture during the formation of clouds and thereby contribute to an increase in cloudiness. And this, in turn, reduces the influx of solar heat to the earth's surface.
Transparency for solar rays in the lower layers of the earth's atmosphere also depends on fires. Due to fires, dust and soot rise into the atmosphere, which cover the Earth with a dense screen and increase the surface albedo.
Which statements are true?
A. Aerosols reflect sunlight and thus contribute to a decrease in the Earth's albedo.
B. Volcanic eruptions contribute to an increase in the Earth's albedo.
1) only A
2) only B
3) both A and B
4) neither A nor B
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The table shows some characteristics for the planets of the solar system - Venus and Mars. It is known that the albedo of Venus A 1= 0.76, and the albedo of Mars A 2= 0.15. Which of the characteristics mainly influenced the difference in the albedo of the planets?
1) A 2) B 3) IN 4) G
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Does the Earth's albedo increase or decrease during volcanic eruptions? Explain the answer.
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Surface albedo is understood as
1) the total amount of sunlight falling on the earth's surface
2) the ratio of the energy flux of reflected radiation to the flux of absorbed radiation
3) the ratio of the energy flux of reflected radiation to the flux of incident radiation
4) the difference between the incident and reflected radiation energy
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Spectra study
All heated bodies radiate electromagnetic waves. To experimentally investigate the dependence of the radiation intensity on the wavelength, it is necessary:
1) expand the radiation into a spectrum;
2) measure the energy distribution in the spectrum.
To obtain and study spectra, spectral devices - spectrographs - are used. The scheme of the prism spectrograph is shown in the figure. The studied radiation first enters the tube, at one end of which there is a screen with a narrow slit, and at the other end there is a converging lens L 1 . The slit is at the focus of the lens. Therefore, a divergent light beam that enters the lens from the slit exits it in a parallel beam and falls on the prism R.
Since different frequencies correspond to different refractive indices, parallel beams of different colors come out of the prism, which do not coincide in direction. They fall on the lens L 2. At the focal length of this lens is a screen, frosted glass or photographic plate. Lens L 2 focuses parallel beams of rays on the screen, and instead of a single image of the slit, a whole series of images is obtained. Each frequency (more precisely, a narrow spectral interval) has its own image in the form of a colored strip. All these images together
and form a spectrum.
The radiation energy causes the body to heat up, so it is enough to measure the body temperature and use it to judge the amount of energy absorbed per unit time. As a sensitive element, one can take a thin metal plate covered with a thin layer of soot, and by heating the plate one can judge the radiation energy in a given part of the spectrum.
The decomposition of light into a spectrum in the apparatus shown in the figure is based on
1) light dispersion phenomenon
2) phenomenon of light reflection
3) light absorption phenomenon
4) thin lens properties
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In the device of a prism spectrograph, the lens L 2 (see figure) is used for
1) decomposition of light into a spectrum
2) focusing rays of a certain frequency into a narrow strip on the screen
3) determining the intensity of radiation in different parts of the spectrum
4) converting a divergent light beam into parallel beams
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Is it necessary to cover the metal plate of the thermometer used in the spectrograph with a layer of soot? Explain the answer.
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Release 3In the video lesson of physics from the Academy of Entertaining Sciences, Professor Daniil Edisonovich continues the conversation about light that began in the previous series of the program. What is the reflection of light viewers already know, but what is the refraction of light? It is the refraction of light that explains some of the strange optical phenomena that we can observe in our daily lives.
The phenomenon of refraction of light
Why do the legs of people standing in the water seem shorter than they really are, and if you look at the bottom of the river, it seems closer? It's all about the refraction of light. Light always tries to move in a straight line, in the shortest way. But getting from one physical medium to another part of the sun's rays changes direction. In this case, we are dealing with the phenomenon of light refraction. That is why the spoon in a glass of tea appears broken - the light from the part of the spoon that is in the tea reaches our eyes at a different angle than the light from the part of the spoon that is above the surface of the liquid. The refraction of light in this case occurs at the border of air with water. When reflected, a ray of light travels the shortest path, and when refracted, it travels the fastest. Using the laws of reflection and refraction of light, people have created many things without which our life is unthinkable today. Telescopes, periscopes, microscopes, magnifying glasses, all this would be impossible to create without knowledge of the laws of refraction and reflection of light. A magnifying glass magnifies because, having passed through it, the rays of light enter the eye at an angle greater than the rays reflected from the object itself. To do this, the object must be placed between the magnifying glass and its optical focus. Optical focus; this is the point at which the initially parallel rays intersect (focus) after passing through the collecting system (or where their continuations intersect if the system is scattering). A lens (such as the lens of eyeglasses) has two sides, so a beam of light is refracted twice - entering and exiting the lens. The surface of the lens can be convex, concave or flat, which determines exactly how the phenomenon of light refraction will occur in it. If both sides of a lens are convex, it is a converging lens. Refracted in such a lens, the rays of light are collected at one point. It is called the main focus of the lens. A lens with concave sides is called divergent. At first glance, it is devoid of focus, because the rays, passing through it, scatter, diverge to the sides. But if we redirect these rays back, then they, having passed through the lens again, will gather at a point, which will be the focus of this lens. There is a lens in the human eye, it is called the lens. It can be compared to a movie projector that projects an image onto a screen, the back wall of the eye (the retina). So it turns out that the lake is a giant lens that causes the phenomenon of light refraction. That is why the legs of the fishermen standing in it seem to be short. The rainbow also appears in the sky because of the lenses. In their role are the smallest droplets of water or particles of snow. A rainbow occurs when sunlight is refracted and reflected by water droplets (rain or fog) floating in the atmosphere. These droplets deflect light of different colors differently. As a result, white light is decomposed into a spectrum (light dispersion occurs). The observer, who stands with his back to the light source, sees a multi-colored glow that comes from space in circles (arcs).
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- Participant: Maksimova Anna Alekseevna
- Head: Gusarova Irina Viktorovna
Goal of the work - to study light phenomena and the properties of light in experiments, to consider the three main properties of light: straightness of propagation, reflection and refraction of light in media of different density.
Tasks:
- Prepare equipment.
- Carry out the necessary experiments.
- Analyze and present the results.
- Make a conclusion.
Relevance
In everyday life, we are constantly confronted with light phenomena and their various properties; the work of many modern mechanisms and devices is also associated with the properties of light. Light phenomena have become an integral part of people's lives, so their study is relevant.
The experiments below explain such properties of light as straightness of propagation, reflection and refraction of light.
For providence and description of experiments, the 13th stereotyped edition of A. V. Peryshkin's textbook “Physics. 8th grade." (Drofa, 2010)
Safety
The electrical devices involved in the experiment are fully operational, the voltage on them does not exceed 1.5 V.
The equipment is stably placed on the table, the working order is observed.
At the end of the experiments, electrical appliances are turned off, the equipment is removed.
Experience 1. Rectilinear propagation of light. (p. 149, fig. 120), (p. 149, fig. 121)
Purpose of experience- to prove the rectilinearity of the propagation of light rays in space using a good example.
The rectilinear propagation of light is its property, which we encounter most often. With rectilinear propagation, energy from a light source is directed to any object along straight lines (light rays), without bending around it. This phenomenon can explain the existence of shadows. But in addition to shadows, there are also penumbra, partially illuminated areas. To see under what conditions shadows and penumbras are formed and how light propagates in this case, we will conduct an experiment.
Equipment: an opaque sphere (on a thread), a sheet of paper, a point light source (a flashlight), an opaque sphere (on a thread) smaller in size, for which the light source will not be a point, a sheet of paper, a tripod for fixing the spheres.
Experience progress
Shadow formation
- Let's arrange the objects in the order pocket flashlight-first sphere (fixed on a tripod)-sheet.
- Let's get the shadow displayed on the sheet.
We see that the result of the experiment was a uniform shadow. Suppose that the light propagated in a straight line, then the formation of a shadow can be easily explained: the light coming from a point source along the light beam, touching the extreme points of the sphere, continued to go in a straight line and behind the sphere, which is why the space behind the sphere is not illuminated on the sheet.
Let's assume that the light propagated along curved lines. In this case, the rays of light, bending, would also fall outside the sphere. We would not have seen the shadow, but as a result of the experiment, the shadow appeared.
Now consider the case in which penumbra is formed.
Formation of shade and penumbra
- Let's arrange the objects in the order pocket flashlight-second sphere (fixed on a tripod)-leaf.
- Illuminate the sphere with a flashlight.
- Let's get a shadow, as well as a penumbra, displayed on the sheet.
This time the results of the experiment are shadow and penumbra. How the shadow was formed is already known from the example above. Now, in order to show that the formation of penumbra does not contradict the hypothesis of rectilinear propagation of light, it is necessary to explain this phenomenon.
In this experiment, we took a light source that is not a point, that is, consisting of many points, in relation to a sphere, each of which emits light in all directions. Consider the highest point of the light source and the light beam emanating from it to the lowest point of the sphere. If we observe the movement of the beam behind the sphere to the sheet, then we will notice that it falls on the border of light and penumbra. Rays from similar points going in this direction (from the point of the light source to the opposite point of the illuminated object) create penumbra. But if we consider the direction of the light beam from the above indicated point to the top point of the sphere, then it will be perfectly visible how the beam falls into the penumbra.
From this experience we see that the formation of a penumbra does not contradict the rectilinear propagation of light.
Conclusion
With the help of this experiment, I proved that light propagates in a straight line, the formation of a shadow and penumbra proves the rectilinearity of its propagation.
Phenomenon in life
The straightness of light propagation is widely used in practice. The simplest example is an ordinary lantern. Also, this property of light is used in all devices that include lasers: laser rangefinders, metal cutting devices, laser pointers.
In nature, the property is found everywhere. For example, light penetrating through gaps in the crown of a tree forms a well-defined straight line passing through the shadow. Of course, if we talk about large scales, it is worth mentioning a solar eclipse, when the moon casts a shadow on the earth, due to which the sun from the earth (of course, we are talking about its shaded area) is not visible. If the light did not propagate in a straight line, this unusual phenomenon would not exist.
Experience 2. Law of reflection of light. (p.154, fig. 129)
Purpose of experience- prove that the angle of incidence of the beam is equal to the angle of its reflection.
Reflection of light is also its most important property. It is thanks to the reflected light, which is captured by the human eye, that we can see any objects.
According to the law of light reflection, the rays, incident and reflected, lie in the same plane with a perpendicular drawn to the interface between two media at the point of incidence of the beam; the angle of incidence is equal to the angle of reflection. Let's check whether these angles are equal, in an experiment, where we take a flat mirror as a reflecting surface.
Equipment: a special device, which is a disk with a printed circular scale, mounted on a stand, in the center of the disk there is a small flat mirror located horizontally (such a device can be made at home using a protractor instead of a disk with a circular scale), the light source is an illuminator attached to the edge of the disc or laser pointer, measurement sheet.
Experience progress
- Let's place the sheet behind the device.
- Turn on the illuminator, directing it to the center of the mirror.
- Let's draw a perpendicular to the mirror to the point of incidence of the beam on the sheet.
- Let us measure the angle of incidence (ﮮα).
- Let us measure the resulting reflection angle (ﮮβ).
- Let's write down the results.
- Let's change the angle of incidence by moving the illuminator, repeat steps 4, 5 and 6.
- Let's compare the results (the value of the angle of incidence with the value of the angle of reflection in each case).
The results of the experiment in the first case:
∠α = 50°
∠β = 50°
∠α = ∠β
In the second case:
∠α = 25°
∠β = 25°
∠α = ∠β
It can be seen from experience that the angle of incidence of a light beam is equal to the angle of its reflection. Light hitting a mirror surface is reflected from it at the same angle.
Conclusion
With the help of experience and measurements, I proved that when light is reflected, the angle of its incidence is equal to the angle of reflection.
Phenomenon in life
We encounter this phenomenon everywhere, as we perceive the light reflected from objects with the eye. A striking visible example in nature is the glare of bright reflected light on water and other surfaces with good reflectivity (the surface absorbs less light than it reflects). Also, one should remember the sunbeams that every child can let out with the help of a mirror. They are nothing more than a ray of light reflected from a mirror.
A person uses the law of reflection of light in such devices as a periscope, a mirror reflector of light (for example, a reflector on bicycles).
By the way, by reflecting light from a mirror, magicians created many illusions, for example, the “Flying Head” illusion. The man was placed in a box among the scenery so that only his head was visible from the box. The walls of the box were covered with mirrors inclined towards the scenery, the reflection from which did not allow the box to be seen and it seemed that there was nothing under the head and it was hanging in the air. The sight is unusual and frightening. Reflection tricks also took place in theaters when a ghost had to be shown on the stage. The mirrors were "fogged" and tilted so that the reflected light from the niche behind the stage was visible in the auditorium. An actor playing a ghost has already appeared in the niche.
Experience 3. Refraction of light.(p. 159, fig. 139)
Purpose of experience- prove that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value for two media; prove that the angle of incidence of a light beam (≠ 0°) coming from a less dense medium to a denser one is greater than its angle of refraction.
In life, we often meet with the refraction of light. For example, putting a perfectly straight spoon into a transparent glass of water, we see that its image bends at the border of two media (air and water), although in fact the spoon remains straight.
To better consider this phenomenon, to understand why it occurs and to prove the law of refraction of light (rays, incident and refracted, lie in the same plane with a perpendicular drawn to the interface between two media at the point of incidence of the beam; the ratio of the sine of the angle of incidence to the sine of the angle of refraction is the value is constant for two media) using an example, we will conduct an experiment.
Equipment: two media of different density (air, water), a transparent container for water, a light source (laser pointer), a sheet of paper.
Experience progress
- Pour water into a container, place a sheet behind it at some distance.
- Let us direct a beam of light into water at an angle, ≠ 0°, since at 0° there is no refraction, and the beam passes into another medium unchanged.
- Let us draw a perpendicular to the interface between two media at the point of incidence of the beam.
- Let us measure the angle of incidence of the light beam (∠α).
- Let us measure the angle of refraction of the light beam (∠β).
- Let's compare the angles, make up the ratio of their sines (to find the sines, you can use the Bradis table).
- Let's write down the results.
- Let's change the angle of incidence by moving the light source, repeat steps 4-7.
- Let's compare the values of the sine ratios in both cases.
Let us assume that light rays, passing through media of different densities, experienced refraction. In this case, the angles of incidence and refraction cannot be equal, and the ratios of the sines of these angles are not equal to one. If there was no refraction, that is, the light passed from one medium to another without changing its direction, then these angles will be equal (the ratio of the sines of equal angles is equal to one). To confirm or refute the assumption, consider the results of the experiment.
The results of the experiment in the first case:
∠α = 20
∠β = 15
∠α >∠β
sin∠α = 0.34 = 1.30
sin∠β 0.26
The results of the experiment in the second case:
∠α ˈ= 50
∠β ˈ= 35
∠α ˈ > ∠β ˈ
sin∠α ˈ= 0.77 = 1.35
sin∠β ˈ 0.57
Comparison of sine ratios:
1.30 ~1.35 (due to measurement errors)
sin∠α = sin∠α ˈ = 1.3
sin∠β sin∠β ˈ
According to the results of the experiment, when light is refracted from a less dense medium to a denser one, the angle of incidence is greater than the angle of refraction. the ratios of the sines of the incident and refracted angles are equal (but not equal to one), that is, they are a constant value for the two given media. The direction of the beam when it enters a medium of a different density changes due to a change in the speed of light in the medium. In a denser medium (here, in water), light propagates more slowly, and therefore the angle of passage of light through space changes.
Conclusion
With the help of the experiment and measurements, I proved that when light is refracted, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value for both media, when light rays pass from a less dense medium to a denser one, the angle of incidence is less than the angle of refraction.
Phenomenon in life
We also meet with the refraction of light quite often; one can give many examples of the distortion of the visible image when passing through water and other media. The most interesting example is the occurrence of a mirage in the desert. A mirage occurs when light rays passing from warm layers of air (less dense) to cold layers are refracted, which can often be observed in deserts.
Human refraction of light is used in various devices containing lenses (light is refracted when passing through a lens). For example, in optical instruments such as binoculars, a microscope, a telescope, in cameras. Also, a person changes the direction of light by passing it through a prism, where the light is refracted several times, entering and exiting it.
The objectives of the work have been achieved.
The Greek astronomer Claudius Ptolemy (circa 130 AD) is the author of a remarkable book that served as the main textbook on astronomy for almost 15 centuries. However, in addition to the astronomical textbook, Ptolemy also wrote the book Optics, in which he outlined the theory of vision, the theory of flat and spherical mirrors, and the study of the phenomenon of light refraction. Ptolemy encountered the phenomenon of light refraction while observing the stars. He noticed that a beam of light, passing from one medium to another, "breaks". Therefore, a stellar ray, passing through the earth's atmosphere, reaches the surface of the earth not in a straight line, but along a curved line, that is, refraction occurs. The curvature of the beam path occurs due to the fact that the air density changes with height.
To study the law of refraction, Ptolemy conducted the following experiment. He took the circle and fixed it on the axis of the ruler l 1 and l 2 so that they can freely rotate around it (see figure). Ptolemy immersed this circle in water up to the diameter AB and, turning the lower ruler, ensured that the rulers lay for the eye on one straight line (if you look along the upper ruler). After that, he took the circle out of the water and compared the angles of incidence α and refraction β. He measured angles with an accuracy of 0.5°. The numbers obtained by Ptolemy are presented in the table.
Ptolemy did not find a "formula" for the relationship between these two series of numbers. However, if you determine the sines of these angles, it turns out that the ratio of the sines is expressed by almost the same number, even with such a rough measurement of the angles that Ptolemy resorted to.
- Task #161772
Refraction in the text refers to the phenomenon
changes in the direction of propagation of a light beam due to reflection at the boundary of the atmosphere
changes in the direction of propagation of a light beam due to refraction in the Earth's atmosphere
absorption of light as it propagates through the earth's atmosphere
light beam bending around obstacles and thus deviations from rectilinear propagation
- Task #90B309
In a calm atmosphere, the positions of stars that are not perpendicular to the surface of the Earth at the point where the observer is located are observed. What is the apparent position of the stars - above or below their actual position relative to the horizon? Explain the answer.
- Task #DCF7E6
Which of the following conclusions contradicts Ptolemy's experiments?
the angle of refraction is less than the angle of incidence when the beam passes from air to water
as the angle of incidence increases, the angle of refraction increases linearly
the ratio of the sine of the angle of incidence to the sine of the angle of refraction does not change
the sine of the angle of refraction depends linearly on the sine of the angle of incidence
- Task #EEB9E2
Due to the refraction of light in a calm atmosphere, the apparent position of the stars in the sky relative to the horizon
above actual position
below actual position
shifted in one direction or another vertically relative to the actual position
matches the actual position
auroras
It is well known that in places on the globe located beyond the northern or southern Arctic Circle, during the polar night, a glow of various colors and shapes flashes in the sky. This is the aurora borealis. Sometimes it looks like a homogeneous arc, fixed or pulsating, sometimes it seems to consist of many rays of different lengths, which shimmer, twist in the form of ribbons, etc. The color of this glow is yellowish-green, red, gray-violet. For a long time the nature and origin of the auroras remained mysterious, and only recently have they been explained. It was possible to establish that auroras occur at an altitude of 80 to 1000 km above the earth, most often at an altitude of about 100 km. Further, it was found that the auroras are the glow of rarefied gases of the earth's atmosphere.
A connection has been observed between the auroras and a number of other phenomena. Long-term observations have shown that the periods of maximum frequency of auroras regularly repeat at intervals of 11.5 years. During each such period of time, the number of auroras first decreases from year to year, and then begins to increase, reaching a maximum after 11.5 years.
It turned out that also periodically, with a period of 11.5 years, the shape and position of dark spots on the solar disk change. At the same time, in the years of maximum sunspots, or, as they say, in the years of maximum solar activity, the number of auroras also reaches a maximum. The change in the number of magnetic storms has the same periodicity; their number also reaches a maximum in years with the highest solar activity.
Comparing these facts, scientists came to the conclusion that spots on the Sun are the places from which streams of charged particles - electrons - are ejected into space with great speed. Once in the upper layers of our atmosphere, high-energy electrons ionize its constituent gases and make them glow.
These same electrons affect the Earth's magnetic field. Charged particles emitted by the Sun, approaching the Earth, fall into the earth's magnetic field. Electrons moving in a magnetic field are affected by the Lorentz force, which deflects them from their original direction of motion. It was shown that charged particles deflected by the Earth's magnetic field can only reach the subpolar regions of the globe. This theory is in good agreement with a large number of facts and is currently generally accepted.
- Task #16D4EC
What is aurora?
electrical discharge in the atmosphere
electric current in the electrolyte, which is moist air
glow of rarefied gases of the earth's atmosphere
radiation of energy from the sun
- Task №AFAFAB
Why are auroras observed in the polar regions?
A. Charged particles are so deflected by the Earth's magnetic field that they can only enter the subpolar regions of the Earth.
B. The atmosphere in the subpolar regions is the most rarefied, and electrons can acquire a sufficiently large energy before colliding with molecules.
The correct answer is
neither A nor B
- Quest #E3C44B Postpone Mark as solved
What is the nature of auroras?
ionization by fast electrons of gas molecules that make up air
glow of gases emitted every second by the Sun into the space between the planets
the glow of fast electrons ejected by the sun
the glow of air currents rising from the earth
Camouflage and uncamouflage
The color of different objects illuminated by the same light source (for example, the Sun) is very diverse. When considering an opaque object, we perceive its color depending on the radiation that is reflected from the surface of the object and enters our eyes.
The fraction of the light flux reflected from the body surface is characterized by the reflection coefficient ρ. White bodies reflect all radiation incident on them (reflection coefficient ρ is close to unity for all wavelengths), black bodies absorb all radiation incident on them (reflection coefficient ρ is almost zero for all wavelengths). The reflection coefficient can depend on the wavelength, due to which there are various colors of the bodies around us.
An object whose reflectance has almost the same values for all wavelengths as the surrounding background becomes indistinguishable even in bright light. In nature, in the process of natural selection, many animals have acquired a protective coloration (mimicry).
This is also used in military affairs for color camouflage of troops and military facilities. In practice, it is difficult to achieve that for all wavelengths the reflection coefficients of the object and the background coincide. The human eye is most sensitive to the yellow-green part of the spectrum, therefore, when masking, they try to achieve equality in the reflection coefficients, first of all, for this part of the spectrum. However, if the objects masked with such a calculation are not observed with the eye, but photographed, then the masking may lose its significance. Indeed, violet and ultraviolet radiation is particularly strong on the photographic plate. The imperfection of the camouflage will also clearly affect if one observes through a light filter, which practically eliminates those wavelengths for which the camouflage is designed.
Quest #B9EC71
What color will green grass appear when viewed through a red filter? Explain the answer.
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