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Dispersion of light Lesson for studying new material Grade 11 Physics teacher Tulyupa Iraida Borisovna Municipal budgetary educational institution "Secondary school No. 17" of the city of Ryazan

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The world around us plays with colors: we are pleased and excited by the blueness of the sky, the greenery of grass and trees, the red glow of the sunset, the seven-color arc of the rainbow. How can one explain the amazing variety of colors in nature?

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The purpose of the lesson: to give a concept of the dispersion of light, to explain the dispersion from the point of view of electromagnetic theory, to explain the origin of the colors of the bodies around us

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Isaac Newton - English physicist and mathematician, while improving telescopes, drew attention to the fact that the image given by the lens is colored around the edges (1643 -1727)

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The experience of I. Newton Passing through the prism, the sunlight was refracted and gave an image on the wall with a rainbow alternation of colors

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The spectral composition of light Isaac Newton was the first to pay attention to the spectral composition of light. The scientist found out that the iridescent strip was formed due to different values ​​​​of the deflection of rays of different colors, i.e. rays with different wavelengths. This is how Newton discovered the dispersion of light.

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Rainbow stripe - spectrum from the Latin "spectrum" - vision Every hunter wants to know where the pheasant sits

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Closing the hole with red glass, Newton observed only a red spot on the wall. One color wave - monochromatic

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Closing the hole with blue glass, Newton observed only a blue spot on the wall Wave of one color - monochromatic

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Different degrees of refraction are associated with different speeds of propagation of light of different frequencies in a given medium. The dependence of the refractive index of light on the oscillation frequency (or wavelength) is called dispersion. Due to the different degree of refraction of different monochromatic colors, a beam of white light is decomposed by a prism into a spectrum.

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Synthesis of white light with the help of prisms By collecting the colored beams emerging from the prism with a lens, Newton received a white image of a hole on a white screen instead of a colored strip

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Conclusions from Newton's experiments: the prism does not change the light, but only decomposes it into its component parts; white light as an electromagnetic wave consists of seven monochromatic waves; light beams that differ in color differ in the degree of refraction; violet rays are most strongly refracted, red ones are less than others; red light has the highest speed in the medium, and violet - the smallest, so the prism decomposes the light.

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Dispersion explains many natural phenomena: Rainbow Colors of opaque bodies Colors of transparent bodies Game of precious stones

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Rainbow A rainbow is a spectrum of sunlight It is formed by the decomposition of white light in raindrops Wide multi-colored beams of light come out of raindrops at different angles of refraction An observer, being outside the rain zone, sees a rainbow against the background of clouds illuminated by the sun, at a distance of 1 - 2 km Conditions the occurrence of a rainbow: 1. A rainbow appears only when the sun peeks out from behind the clouds and only in the direction opposite to the sun. 2. A rainbow occurs when the sun illuminates a curtain of rain. 3. A rainbow appears provided that the angular height of the sun above the horizon does not exceed 42º

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Optical phenomena occur in a water drop: Refraction of light Dispersion of light Reflection of light

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The color of opaque objects The variety of colors and shades in the world around us explains the phenomenon of dispersion. When interacting with different bodies, rays of light of different colors are reflected and absorbed by these bodies in different ways. Bodies painted white reflect rays of light of different frequencies equally well. Bodies painted black absorb light rays of different frequencies equally well. Opaque bodies are painted in the color whose rays of light they reflect well.

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Color of transparent bodies The color of a transparent body is determined by the composition of the light that passes through it. If a transparent body uniformly absorbs the rays of all colors, then in transmitted white light it is colorless, and in colored light it has the color of those rays with which it is illuminated. When white light is passed through tinted glass, it lets through the color it is painted with. This property is used in various light filters.

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The play of precious stones The phenomenon of dispersion during repeated refraction of light explains the play of precious stones. Precious stones seem to us colored, since the impurities contained in them absorb some of the components of white light.

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Conclusions: Dispersion is a phenomenon of decomposition of white light into a spectrum. White light is complex, it consists of seven monochromatic colors. The refractive index of a medium depends on the color of light. Light with different wavelengths propagates in a medium at different speeds: violet at the lowest, red at the highest

Ideas about the causes of colors before Newton.

The described experience is, in fact, ancient. Already in the 1st century n. e. it was known that large single crystals (hexagonal prisms made by nature itself) have the property of decomposing light into colors. The first studies of the dispersion of light in experiments with a glass triangular prism were carried out by the Englishman Khariot (1560-1621). Independently of him, similar experiments were made by the famous Czech naturalist Marci (1595 - 1667), who found that each color has its own refractive angle. However, prior to Newton, such observations were not subjected to sufficiently serious analysis, and the conclusions drawn from them were not rechecked by additional experiments. As a result, the science of those times was dominated for a long time by ideas that incorrectly explained the appearance of colors. Speaking about these ideas, one should start with Aristotle's theory of colors (4th century BC). Aristotle argued that the difference in color is determined by the difference in the amount of darkness "mixed" into the sunlight (white) light. Violet color, according to Aristotle, occurs with the greatest addition of darkness to light, and red - with the least. Thus, the colors of the rainbow are complex colors, and the main one is white light. It is interesting that the appearance of glass prisms and the first experiments on observing the decomposition of light by prisms did not give rise to doubts about the correctness of the Aristotelian theory of the origin of colors. Both Khariot and Martzi remained followers of this theory. This should not be surprising, since at first glance, the decomposition of light by a prism into different colors would seem to confirm the idea that color arises as a result of mixing light and darkness. The rainbow strip appears just at the transition from the shadow strip to the illuminated one, i.e., at the border of darkness and white light. From the fact that the violet ray travels the longest distance inside the prism compared to other colored rays, it is not surprising to conclude that the violet color occurs when white light loses its “whiteness” the most when passing through the prism. In other words, on the longest path, the greatest mixing of darkness with white light occurs. It was not difficult to prove the falsity of such conclusions by setting up the corresponding experiments with the same prisms. However, no one had done this before Newton.

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Presentation - Light dispersion

The text of this presentation

Physics lesson in 11 (8) class

Light dispersion

ANNOTATION:
The presentation allows you to conduct a lesson on the topic: "Dispersion of light" The presentation is designed to enhance the cognitive activity of students. development of thinking, initiative in acquiring knowledge, development of interest in the study of physics. Computer support of the lesson can be used to enrich its content. Used ITC: working with text, drawings, searching for illustrative material on the Internet, scanning. The presentation consists of 20 slides, the amount of memory is 2.11KB

Goals:
1 To get acquainted with the concept of light dispersion, to study the wave properties of light; 2 Explain the rainbow phenomenon based on physical concepts; 3 Find out what color is.

Epigraph
How unexpectedly and brightly On the wet blue sky, an airy arch was erected In its momentary triumph! She plunged one end into the forests, She left behind the clouds with the other, She embraced half the sky And fainted in the height. F.I. Tyutchev

Introduction to the phenomenon
300 years ago, the English physicist Isaac Newton, studying the phenomenon of refraction of light passing through a glass prism, discovered an amazing phenomenon. A beam of sunlight, falling on a prism, is refracted, and a multi-colored strip of light appears on the opposite wall, which is called the SPECTRUM. Thus, white light is a "wonderful mixture of colors."

7 COLORS OF THE DISPERSION SPECTRUM:
1 RED 2 ORANGE 3 YELLOW 4 GREEN 5 BLUE 6 BLUE 7 PURPLE
Spectrum colors

It is interesting …
Why are there only 7 colors in the white light spectrum? Aristotle, for example, indicated only three colors: red, green, purple. Newton first identified five colors, and later ten. However, he later settled on seven colors. The choice is explained, most likely, by the fact that the number "seven" was considered magical (seven wonders of the world, seven days of the week, etc.)

Physical dictionary
Spectrum - from the Latin word spectrum - visible, vision. Dispersion - from the Latin word dispersus - scattered, scattered. Chromatism is from the Greek word for color. Inversion - from the Latin word inversio - turning over, moving.

DEFINITION Dispersion of light - the dependence of the refractive index of a substance on the wavelength (frequency) of light. The phenomenon was discovered by Isaac Newton (1643-1727) in 1666
In glass, the speed of the violet wave is less than the speed of the red, and therefore it, passing through the prism, is refracted more strongly.

RAINBOW
Sometimes, when the sun comes out again after a heavy downpour, you can see a rainbow. This is because the air is saturated with fine water dust. Each drop of water in the air plays the role of a tiny prism, crushing the light into different colors.

Rainbow is a special case of CAUSTIC, the play of light. To see it, you need to stand with your back to the sun after the rain. A multi-colored arc is usually located at a distance of 1-2 km from the observer, and sometimes it can be observed at a distance of 2-3 m against the background of water drops formed by fountains or water sprays.

The center of the rainbow is on the continuation of the straight line connecting the Sun and the eye of the observer - on the counter-solar line. The angle between the direction to the main rainbow and the antisolar line is 41-42 degrees.

How is a rainbow formed?
A rainbow appears as a result of reflection of light from the inner surface of a raindrop and double refraction - when entering and leaving the drop. The rainbow theory was first given in 1637 by René Descartes.

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

Why do we sometimes see a second rainbow?
The reason for the second rainbow, like the first, is the refraction and reflection of light in water droplets. However, before turning into a “second rainbow”, the rays of sunlight have time to reflect twice, and not once, from the inner surface of each droplet.

Please note that the sequence of colors in the "second rainbow" is REVERSE to that seen in the "primary". The brightness of the "second rainbow" is less than the first due to the fact that both internal reflections are not complete and part of the light comes out of the drop.

Why is the rainbow round?
The fact is that each raindrop has an approximately spherical shape, and the parallel beam of sunlight falling on it turns into a multi-colored circle as a result of refraction and internal reflection.

In the eye of the observer, as in the top of a circular cone with an angle at the top of 42 degrees, rays are collected, diverging from many droplets and forming a circle of the same angular size. If the "eye" moves, the whole rainbow picture moves - in each specific place it forms its own set of droplets.

Light dispersion

The psychological impact of light.
Psychological research in the middle of the twentieth century. showed that each color has a very specific psychophysical effect, independent of the individual characteristics of a person. Differences occur at the level of the psychological reaction of each person to a particular color. Red. Contributes to the treatment of all viral diseases., Stimulates the immune system. Strengthens memory, invigorates energy throughout the body, increases muscle strength. Orange. Increases the level of neuroendocrine regulation, has a rejuvenating effect on the entire body. Yellow. Produces a cleansing effect on the entire body. Stimulates appetite. This is a physiologically optimal color, it tones the nervous system, stimulates vision.

The psychological impact of light. (continued)
Green. Normalizes cardiac activity, calms the central nervous system. This is the color of relaxation, relieving nervous tension. Blue. Contributes to the normalization of blood pressure, cardiac activity. It is used in the treatment of diseases of the eyes and liver. Blue. It has an unusually beneficial effect on the entire endocrine system. Treats diseases of the lungs and eyes. Violet. It has a calming effect on the nervous system. It has a positive effect on the vascular system.

GAME "Find your color"
RED 1 A AND C ORANGE 2 BY T Y YELLOW 3 B G GREEN 4 GL V CYAN 5 D M HYU BLUE 6 EN C Y PURPLE 7 Y O BLACK PINK 8 Y R W GOLD 9 Z R Щ Write your name (last name, nickname, abbreviation, etc.), fill in the appropriate numbers and sum them up. If the result is a number greater than 10, add up its digits and continue with the resulting numbers until the sum is less than 10. Similarly, to determine the color of the date of birth, sum the digits of its constituent numbers. TRY TO MATCH YOUR BOTH COLORS.

PROVERBS, SAYINGS, RIDDLES
High and steep rainbow - to the bucket, flat and low - to bad weather. Rainbow - arc, interrupt the rain. The bridge stretched for seven villages, for seven miles. Shirt outside, sleeves in the hut. A painted yoke hung across the river. A red cloth stretches through the window. You look - you cry, but there is no more beautiful than him in the world. Find proverbs and sayings related to the studied phenomena.

Answer the questions:
1 Why is white light able to decompose into a spectrum when passing through a glass prism? 2 Who discovered the phenomenon of dispersion? 3 What is dispersion? 4 How to explain the variety of colors visible to man in nature? 5 How do different colors differ from each other? 6 What is a rainbow? Why do we see the sky blue and the dawn red?

Consequences
White light is a set of waves of different frequencies.
A substance selectively absorbs light waves of different frequencies.
Getting into the human eye, light waves of different frequencies have a different effect on the retina.
Each color has its own wave frequency.

"FRAGRANCE OF THE SUN" The smell of the sun? What nonsense! No, not nonsense.
In the sun, sounds and dreams, Aromas and flowers, All merged into a consonant choir, All intertwined into one pattern. The sun smells of herbs, Fresh kupava, Awakened in the spring And resinous pine, Gently - light-woven, Drunk lilies, That triumphantly blossomed In the pungent smell of the earth.
The sun shines with ringing, Green leaves, Breathes the spring song of birds, Breathes the laughter of young faces. So say to all the blind: It will be for you! You will not behold the gates of paradise, The sun has a fragrance, Sweetly intelligible only to us, Visible to birds and flowers! K. Balmont

Literature:
1 “The first of September. Physics”, No. 33/03; 11/04; 3/06; 6/06; 2 S.V. Zvereva "In the world of sunlight"; L.: Gidrometeoizdat, 1988 3 V.L. Bulat "Optical phenomena in nature"; M.; Enlightenment, 1985 4 G. Ya. Myakishev, B. B. Bukhovtsev "Physics. Grade 11", M .; Education, 2006-2007 5 A.I. Semke "Physics. Entertaining materials for lessons "; M.; NTs ENAS, 2006

A zebra and a rainbow are somewhat similar: A zebra is striped, a rainbow too. Let life be a striped zebra, But not two-color, but multi-colored! life illuminates with love. Blue - will raise you above the vanity. It will be a bright and good dream! I wish you such colors, great happiness and longevity!

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