Light dispersion briefly and clearly the most important. Light dispersion, color and person

) light (frequency dispersion), or, the same thing, the dependence of the phase velocity of light in matter on frequency (or wavelength). Experimentally discovered by Newton around 1672, although theoretically well explained much later.

Spatial dispersion is the dependence of the dielectric permittivity tensor of a medium on the wave vector . This dependence causes a number of phenomena called spatial polarization effects.

Encyclopedic YouTube

1 / 3

Dispersion and spectrum of light

Light dispersion and body color

dispersion of light. Phone colors.

Subtitles

Properties and manifestations

One of the most illustrative examples of dispersion is the decomposition of white light as it passes through a prism (Newton's experiment). The essence of the phenomenon of dispersion is the difference in the phase velocities of propagation of light rays with different wavelengths in a transparent substance - an optical medium (whereas in vacuum the speed of light is always the same, regardless of the wavelength and hence the color). Usually, the shorter the wavelength of light, the greater the refractive index of the medium for it and the lower the phase velocity of the wave in the medium:

• for red light, the phase velocity of propagation in the medium is maximum, and the degree of refraction is minimum,
• for violet light, the phase velocity of propagation in the medium is minimal, and the degree of refraction is maximum.

However, in some substances (for example, in iodine vapor) the effect of anomalous dispersion is observed, in which blue rays are refracted less than red ones, while other rays are absorbed by the substance and escape observation. Strictly speaking, anomalous dispersion is widespread, for example, it is observed in almost all gases at frequencies near the absorption lines, but in iodine vapor it is quite convenient for observation in the optical range, where they absorb light very strongly.

The dispersion of light made it possible for the first time to quite convincingly show the composite nature of white light.

Augustin Cauchy proposed an empirical formula for approximating the dependence of the refractive index of a medium on the wavelength:

Where λ (\displaystyle \lambda )- wavelength in vacuum; a, b, c- constants, the values ​​of which for each material must be determined in the experiment. In most cases, you can restrict yourself to the first two terms of the Cauchy formula. Subsequently, other more accurate, but at the same time more complex, approximation formulas were proposed.

Light dispersion (light decomposition) is a phenomenon of the dependence of the absolute refractive index of a substance on the wavelength of light (frequency dispersion), as well as on the coordinate (spatial dispersion), or, equivalently, the dependence of the phase velocity of light in a substance on the wavelength ( or frequency). Experimentally discovered by Newton around 1672, although theoretically well explained much later.

One of the most illustrative examples of dispersion is the decomposition of white light as it passes through a prism (Newton's experiment). The essence of the phenomenon of dispersion is the unequal speed of propagation of light rays with different wavelengths in a transparent substance - an optical medium (whereas in vacuum the speed of light is always the same, regardless of the wavelength and hence the color).

Usually, the higher the frequency of the wave, the higher the refractive index of the medium and the lower its speed of light in it:

Red is the maximum speed in the medium and the minimum degree of refraction,

Violet is the minimum speed of light in the medium and the maximum degree of refraction.

Anomalous dispersion- a type of light dispersion, in which the refractive index of the medium decreases with increasing frequency of light vibrations.

where is the refractive index of the medium,

is the frequency of the wave.

According to modern concepts, both normal and anomalous dispersions are phenomena of the same nature. This point of view is based on the electromagnetic theory of light, on the one hand, and on the electronic theory of matter, on the other. The term "anomalous dispersion" today retains only a historical meaning, since "normal dispersion" is a dispersion far from the wavelengths at which light is absorbed by a given substance, and "anomalous dispersion" is a dispersion in the region of light absorption bands by a substance.

The difference between anomalous dispersion and normal dispersion is that in some substances (for example, in iodine vapor), when light is decomposed when passing through a prism, blue rays are refracted less than red ones, while other rays are absorbed by the substance and escape observation. In normal dispersion, on the contrary, red light is refracted through an angle smaller than that through which violet is refracted. (For more details, see the topic "Dispersion").

The dispersion of light made it possible for the first time to quite convincingly show the composite nature of white light. White light is also decomposed into a spectrum as a result of passing through a diffraction grating or reflecting from it (this is not related to the phenomenon of dispersion, but is explained by the nature of diffraction). The diffraction and prismatic spectra are somewhat different: the prismatic spectrum is compressed in the red part and stretched in the violet and is arranged in descending order of wavelength: from red to violet; the normal (diffraction) spectrum is uniform in all areas and is arranged in ascending order of wavelengths: from violet to red.

Absorption of light - the phenomenon of attenuation of the brightness of light when it passes through a substance or when reflected from a surface. The absorption of light occurs due to the transformation of the energy of a light wave into the internal energy of a substance or into the energy of secondary radiation, which has a different spectral composition and a different direction of propagation.

The Bouguer-Lambert-Beer law is a physical law that determines the attenuation of a parallel monochromatic beam of light as it propagates in an absorbing medium.

The law is expressed by the following formula:

,

where I0 is the intensity of the incoming beam, l is the thickness of the substance layer through which the light passes, and kλ is the absorption index.

The absorption index is a coefficient that characterizes the properties of a substance and depends on the wavelength λ of the absorbed light. This dependence is called the absorption spectrum of the substance.

Color is a qualitative subjective characteristic of electromagnetic radiation in the optical range, determined on the basis of the resulting physiological visual sensation, and depending on a number of physical, physiological and psychological factors. Individual perception of color is determined by its spectral composition, as well as color and brightness contrast with surrounding light sources, as well as non-luminous objects. Phenomena such as metamerism are very important; features of the human eye, and the psyche.

The absorption spectrum is the dependence of the intensity of radiation absorbed by a substance (both electromagnetic and acoustic) on frequency. It is associated with energy transitions in matter. The absorption spectrum is characterized by the so-called absorption coefficient, which depends on frequency and is defined as the reciprocal of the distance at which the intensity of the transmitted radiation flux decreases by a factor of e. For different materials, the absorption coefficient and its dependence on the wavelength are different.

From today's positions normal dispersion- This dispersion away from the wavelengths at which absorption occurs Sveta this substance, while anomalous dispersion- This dispersion in the region of absorption bands Sveta substance.

MOU Alekseevskaya secondary school

Work theme

"Dispersion of light, color and man"

Type of work - problem-abstract

Physics teacher of the 1st qualification category

Stekolnikov Vsilii Georgievich

2010

Introduction ………………………………………………………….. 3

1. Light dispersion ………………………………………………………4

2. A bit of color history ………………………………………….5

3. The influence of color on a person…………………………………………….7

4. What color is your character? ................................................. ............8

5. Color and sound …………………………………………………………..9

6. Therapeutic effect of color ………………………………………..11

7. Blood group and color ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

8. Color of the car and accidents on the road…………………………………… 13

classrooms …………………………………………………….14

10. Conclusion ………………………………………………………… 15

11. List of used literature …………………………….. 16

Introduction

In this work, the following tasks are set:

Reveal interesting facts about how color affects a person’s character, what a healing effect color has, what is the relationship between color and sound, fantastic at first glance the prospects for “color scoring” of the cosmos, what is the relationship between a person’s blood type and color, about what An interesting relationship exists between man and color. The little-studied facts of the existence of a human biofield and any object, their mutual influence on each other, are slightly touched upon. Also, the fact of the skillful use of the influence of the color design of paintings and works by great artists and composers for their better perception by a person at a subconscious level through color.

Show the influence of the color design of classrooms, school corridors, gyms and workshops on the successful learning of students, on their mental state, and, depending on this, health.

1. Light dispersion

Being engaged in the improvement of telescopes, Newton drew attention to the fact that the image given by the lens is colored at the edges. He became interested in this and was the first to "investigate the diversity of light rays and the peculiarities of colors resulting from this, which no one had even suspected before" (words from the inscription on Newton's tombstone). The iridescent coloration of the image given by the lens was observed, of course, before it. It has also been noticed that iridescent objects are viewed through a prism. The beam of light rays passing through the prism is colored at the edges.

https://pandia.ru/text/78/320/images/image002_36.jpg" width="124" height="112">
I. Newton () Newton's experiment Dispersion of light

Newton's basic experiment was ingeniously simple. He guessed to send a light beam of small cross section to the prism. A beam of sunlight entered the darkened room through a small hole in the wall. Falling on a glass prism, it refracted and gave on the opposite wall an elongated image with iridescent alternation of colors. Following the centuries-old tradition that the rainbow was considered to consist of 7 colors, Newton also identified 7 colors: purple, blue, blue, green, yellow, orange, red. Newton called the rainbow strip itself a spectrum.

https://pandia.ru/text/78/320/images/image005_27.jpg" align="left" width="150" height="100 src=">

Types of spectra

Newton's important conclusion was formulated by him in his treatise on "Optics" as follows: "Light rays that differ in color differ in their degree of refraction." Violet rays are most strongly refracted, red ones are less than others. Newton called the dependence of the refractive index of light on its color dispersion.

2. A bit of color history

There was such a case in England. Residents of houses located opposite complained to the court about their neighbor. The fact is that the canary color, in which the Englishman painted the facade of his house, and the black frames caused a headache among the locals. By order of the court, the owner of the bright mansion was forced to repaint it.

Koll" href="/text/category/koll/" rel="bookmark">colleagues Russian textile factories in the 90s produced mainly fabrics of three gloomy colors; gray, brown and black. According to psychologists, such a color scheme The complex colors of withered autumn, last year's leaves and withering, beloved by post-perestroika Russians, are called by psychologists dirty, rotten and unhealthy.

The development of color is associated with a 100-year cycle, says Svetlana Zhuchenkova, candidate of sciences, one of the first Russian scientists-colorists, teacher at the Moscow Textile Academy. The end of the century, as a rule, corresponds to complex colors; lilac, swamp green, gray-blue, as well as pale and delicate colors. simple colors; white, black, red and yellow are more typical for the beginning of the century.

At the same time, national psychology cannot be ignored. So, for example, if in America a man goes to work in a brown suit, then he is unlikely to get this job. The French prefer sharp tones and love contrasts, the Italians prefer softer colors. Asia tends to yellow, blue and a little vulgar, red, the Balts - to green and brown. Moscow is notable for its variegated range, and St. Petersburg - for its "aesthetic" one.

https://pandia.ru/text/78/320/images/image009_25.jpg" width="109" height="150">

At one time, Stalin, following the example of Napoleon, who created an elaborate and pompous color style to perpetuate the splendor of his victories in architecture and painting, demanded that portals and arches be built in the majestic style of Napoleon, demonstrating his own greatness with the face of the country. The leader of the peoples treated the color scheme more severely. Of the 160 flowers, each of which had its own name in Tsarist Russia, only a few dozen have survived. Post-revolutionary colors in the history of coloring in Russia are generally absent as a genre. There were limited colors during the Stalin era. In the 40s and 50s, the country was dressed in steel gray and green tones, in the 60s the colors of increasing labor productivity were used. Fluorescent dyes were developed in the 70s. According to some reports, almost all the developers of these poisonous flowers died of cancer.

https://pandia.ru/text/78/320/images/image011_20.jpg" align="left" width="106" height="136 src=">

3. The influence of color on a person.

There is a strange and complicated relationship between man and color. According to scientists, color is not just an element of aesthetics and culture, but rather a complex mental substance that demonstrates a person’s mood, his state of mental health, and even can influence him.

https://pandia.ru/text/78/320/images/image014_16.jpg" width="276" height="360 src=">

Red color activates muscle strength. Psychologists say that if a weightlifter wears red glasses, he will “take” more weight than without them. At the same time, being surrounded by "red", a person will try to get out of it faster. Red telephone boxes were designed for high traffic. Children almost also react to this color. A child sleeping facing a wall with red wallpaper is more irritable and restless.

Purple could replace drug addicts with a hallucinogen. If a person is put in a room where everything: the ceiling, floor, walls, windows and doors are painted purple, then he will begin to hallucinate.

Blue color promotes reflection, calms and reduces pressure.

Blue sets melancholy.

White color creates a sense of unreality.

Black color the most complex, on the one hand, mystical, symbolizing dedication to something inaccessible to others, on the other hand, official.

4. What color is your character?

Psychologists say that a person's character can be determined by his color tastes. By the way, the Swiss scientist M. Lumar came to such conclusions. He believes that if you like the color red, then your main features are a strong will, quick decision making. Preference for yellow indicates that you are an optimist and an idealist. You like everything new, unexpected, unusual and sensational.

If you like the color orange, then you tend to easily perceive successes and failures, you have enough will to make decisions. You are strong physically and mentally.

If you like the color green, then you are self-confident and critical person. You are solid, conservative, you know your worth. You are almost perfect in family life.

If you are attracted to blue or blue, then you are a person of a weak character, emotional and good-natured, with a rich inner life.

If you like the color purple, then you are more of an intuitionist than a logician.

5. Color and sound

The connection between color and sound is most clearly expressed in the phenomenon of color music. Color music was close to the composer, who preferred to create his works in a specific key for a given color. The music of color was one of the main elements in many of the artist's paintings. For the first time, the composer succeeded in the large-scale implementation of color and musical influence in the symphonic poem "Prometheus" ("Poem of Fire", 1910). To enhance the impact of music, he introduced an organ, bells into the orchestra, used the sound of the choir without words and special lighting ("parts of color").

Roerich's paintings:

https://pandia.ru/text/78/320/images/image016_19.jpg" width="128" height="128">

A person's perception of musical works simultaneously with a certain color scheme of light significantly affects the impression of using these works. First of all, because the sensitivity of the eye and ear are interconnected. So, the sensitivity of the eye to the green-blue rays of the visible spectrum under the influence of sounds and noise noticeably increases, and to orange-red it decreases; the sensitivity of our hearing aid decreases with increasing light intensity. It is also influenced by the fact that the fastest person perceives objects of red color and the slowest of all, objects of purple color. And since the world in colors is always perceived by a person as sharper and deeper than a gray background, the author of music has the opportunity to use the features of a person’s color vision to enhance the impact of music on him.

Doctors have long established that major music accelerates the secretion of digestive juices in the body, has an exciting effect on the human body, mainly accelerates the rhythms of breathing and heartbeat. Its impact is enhanced if orange-red tones are used in the coloring of rooms and objects. Melodious music causes a person to slow down breathing; music therapy is based on the perception of quiet, non-anxious sounds in a person. Its effectiveness is enhanced if it is carried out in a room dominated by blue-green color tones.

This is no coincidence. Psychologically, red colors excite and alert a person - this is the color of fire and blood, and in the historically developed ideas of a person, they serve as harbingers of trouble. Blue-green tones are the colors of fresh vegetation and clear skies; they are not usually associated with danger. Thus, color affects the psycho-physiological state of a person, his perception of various phenomena, including music.

The reverse process is also observed. When comparing major and minor melodies, most people who love music have a feeling of chiaroscuro, because the major is identified with the "light" mode, and the minor with the "dark" one. This takes place, for example, when perceiving the picture of dawn in the introduction to the opera "Khovanshchina" and the picture of the night sky in the introduction to the opera "The Night Before Christmas" by Korsakov.

https://pandia.ru/text/78/320/images/image019_14.jpg" width="150" height="112">

In addition to the "multi-color" that accompanies the sound of music, its range of influence can be expanded by the use in orchestras of musical instruments with a special sound spectrum - both old, but not widely used (for example, the invented theremin), and new ones.

https://pandia.ru/text/78/320/images/image021_13.jpg" width="143" height="107">

At the same time, such a fantastic way is possible: to create a special musical instrument and music of extraordinary sound, by recoding the radiation with their rich and original color gamut into the sound spectrum. Despite the seeming utopia of the idea, such work was done by the employees of the Paris Astronomical Observatory, who, using electroacoustic technology, converted the light of individual stars into sound frequencies. As a result, the vault of heaven "spoke" to people in the language of sounds. Pythagoras dreamed of the perception of the "music of the heavenly spheres". Now his dream has come true, but in a different way than he expected (not due to the mechanical movement of celestial bodies in their orbits).

6. Healing effect of color

It has long been proven that each person has his own biofield. But as confirmed by special scientific studies, the presence of a biofield is also characteristic of works of art; paintings, sculptures. Moreover, during the experiment, it was possible to prove that through this biofield they can affect our health in some cases more than drugs. By choosing a work and colors, you can normalize blood pressure, calm the nervous system, reduce pain, and relieve stress. With regular treatment with works of art, good results have been noted for neuroses, diseases of the heart, liver, thyroid gland, gallbladder and intestines. In addition, a person receives a strong psycho-emotional impulse, which contributes to the overall improvement of the body.

https://pandia.ru/text/78/320/images/image024_11.jpg" width="92" height="180">

The therapeutic effect of color is associated with the influence of wave vibrations of a certain length on our organs and mental centers, and the action of different colors has a specific effect in certain diseases.

Red color helps with viral diseases, stomach ulcers, anemia, hypotension, stimulates the immune system, the activity of endocrine glands and metabolism, strengthens memory, gives vigor and energy.

Pink color has a sedative effect on the nervous system, improves mood.

Orange color improves the processes of digestion, regeneration, helps with diseases of the spleen and lungs, increases blood circulation.

Yellow effective for atonic constipation, insomnia, skin diseases. It stimulates appetite, has a cleansing effect on the entire body, stimulates vision and liver function, and tones the nervous system. It is considered to be the physiologically optimal color.

Green color normalizes cardiac activity, stabilizes blood pressure, reduces headaches, pain in diseases of the spine, helps with acute colds, improves metabolism and performance.

Blue used for diseases of the eyes, liver, larynx, spine. It reduces appetite and intestinal spasms, normalizes cardiac activity.

Blue color affects the thyroid gland, helps with diseases of the kidneys and bladder, lungs, eyes, treats insomnia, mental illness, jaundice, skin diseases.

Violet color- the color of spirituality and creativity. It has a calming effect on the nervous system, helps with mental disorders, neuralgia, concussions. This color is recommended for diseases of the kidneys, liver, urinary and gallbladder, and various inflammatory processes. Its positive effect on the vascular system has also been noted.

7. Blood type and color

Scientists have found that there is also a close relationship between a person's blood type and color.

1st group blood. The most favorable are red, orange and purple tones.

3rd group. Wider choice. Red and orange colors stimulate vital processes and enhance mental activity. The blue and green tones will calm the nerves, while the purple tone will help create a mood for reflection and remembrance.

4th group. People with this blood type are similar in their energy characteristics to the second one, they should come into contact more often with blue and green.

8. Car color and traffic accidents

According to official figures, silver-colored cars are 50% less likely to get into serious accidents than cars of other colors. White, yellow, grey, red and blue cars have about the same level of risk. Drivers who drive black, brown and green cars are especially at risk because their risk of having an accident and serious injury is increased by 2 times.

https://pandia.ru/text/78/320/images/image026_10.jpg" align="left" width="335" height="209 src=">The most "dangerous" car in terms of the probability of getting into an accident.

The risk is doubled.

Color psychological studies have shown that children prefer one or another color depending on age.

At an early age, they prefer red or purple, with girls being pink.

At the age of 9-11 years, the interest in red is gradually replaced by an interest in orange, then yellow, yellow-green, and then green.

After 12 years, the favorite color is blue.

Chalkboards should be painted dark green or dark blue. You should not create a color contrast on the wall where the board hangs, so as not to tire the students' eyesight. The front wall can in many cases be painted in a color that is more intense than the back and side walls.

In preparatory and first grade, intense pure red tones can be recommended.

For second-graders, red can be gradually replaced by orange-red or orange, for 10-11 year olds - yellow, yellow-green, and then green.

For children of adolescence, blue begins to play a certain role, but always in combination with orange, since a class with a lot of blue creates a "cold" impression.

In classrooms where manual labor is involved, the color blue should be used. The music class should be painted with the same color. In the gym, it is better to use blue and light green colors.

Halls and corridors can be painted light blue and yellow

10. Conclusion

This work is intended to show the great importance of knowledge about the effect of color on the human body, on health, on the mental and physical state, on the effective perception of works of art and music. And the life and safety of a person is directly related, for example, to the color of the car, which of course must be taken into account. At the same time, this direction in physics is little studied, for example, the biofield of a person and objects. Or "poorly lit" in scientific and educational literature. This direction in physics has great prospects for further study.

12. List of used literature

1., Handbook of Physics, 2005

1. Soros Scientific and Educational Journal, 2005, 2006

2. Journal "Physics at school", 2005

Every hunter wants to know where the pheasant is sitting. As we remember, this phrase means the sequence of colors of the spectrum: red, orange, yellow, green, blue, indigo and violet. Who showed that the white color is the totality of all colors, what does the rainbow, beautiful sunsets and sunrises, the brilliance of precious stones have to do with this? All these questions are answered by our lesson, the theme of which is: “Dispersion of light”.

Until the second half of the 17th century, there was no complete clarity about what color is. Some scientists said that this is a property of the body itself, some stated that these are various combinations of light and dark, thereby confusing the concepts of color and illumination. Such color chaos reigned until the time when Isaac Newton conducted an experiment on the transmission of light through a prism (Fig. 1).

Rice. 1. Ray path in a prism ()

Recall that a ray passing through a prism undergoes refraction when passing from air to glass and then another refraction - from glass to air. The ray trajectory is described by the law of refraction, and the degree of deflection is characterized by the refractive index. Formulas describing these phenomena:

Rice. 2. Newton's experience ()

In a dark room, a narrow beam of sunlight penetrates through the shutters; Newton placed a glass trihedral prism in its path. A beam of light, passing through a prism, was refracted in it, and a multi-colored band appeared on the screen behind the prism, which Newton called the spectrum (from the Latin "spectrum" - "vision"). The white color turned into all colors at once (Fig. 2). What conclusions did Newton draw?

1. Light has a complex structure (in modern terms, white light contains electromagnetic waves of different frequencies).

2. Light of different colors differs in the degree of refraction (characterized by different refractive indices in a given medium).

3. The speed of light depends on the medium.

These conclusions Newton outlined in his famous treatise "Optics". What is the reason for such a decomposition of light into a spectrum?

As Newton's experiment showed, the red color was refracted the weakest, and violet the strongest. Recall that the degree of refraction of light rays characterizes the refractive index n. Red differs from violet in frequency, red has a lower frequency than violet. Since the refractive index becomes larger as one goes from the red end of the spectrum to the violet, one can conclude that the refractive index of glass increases with increasing light frequency. This is the essence of the phenomenon of dispersion.

Recall how the index of refraction is related to the speed of light:

n~v; V ~ => ν =

n - refractive index

C is the speed of light in vacuum

V is the speed of light in the medium

ν - light frequency

This means that the higher the frequency of light, the slower the speed of light propagates in the glass, thus, the highest speed inside the glass prism is red, and the lowest speed is violet.

The difference in the speeds of light for different colors is carried out only in the presence of a medium, naturally, in a vacuum, any ray of light of any color propagates with the same speed m/s. Thus, we found out that the reason for the decomposition of white color into a spectrum is the phenomenon of dispersion.

Dispersion- dependence of the speed of propagation of light in the medium on its frequency.

The phenomenon of dispersion, discovered and studied by Newton, was waiting for its explanation for more than 200 years, only in the 19th century the Dutch scientist Lawrence proposed the classical theory of dispersion.

The reason for this phenomenon is the interaction of external electromagnetic radiation, that is, light with the medium: the greater the frequency of this radiation, the stronger the interaction, which means that the more the beam will deviate.

The dispersion that we talked about is called normal, that is, the frequency index increases if the frequency of electromagnetic radiation increases.

In some rare media, anomalous dispersion is possible, that is, the refractive index of the medium increases if the frequency drops.

We have seen that each color has a specific wavelength and frequency. A wave corresponding to the same color in different media has the same frequency, but different wavelengths. Most often, speaking of the wavelength corresponding to a certain color, they mean the wavelength in vacuum or air. The light corresponding to each color is monochromatic. "Mono" - one, "chromos" - color.

Rice. 3. Arrangement of colors in the spectrum by wavelengths in the air ()

The longest wavelength is red (wavelength - from 620 to 760 nm), the shortest wavelength is violet (from 380 to 450 nm) and the corresponding frequencies (Fig. 3). As you can see, there is no white color in the table, white color is the totality of all colors, this color does not correspond to any strictly defined wavelength.

What explains the colors of the bodies that surround us? They are explained by the ability of the body to reflect, that is, to scatter the radiation incident on it. For example, a white color falls on some body, which is a combination of all colors, but this body best reflects red, and absorbs the rest of the colors, then it will appear to us as red. The body that best reflects blue will appear blue, and so on. If the body reflects all colors, it will eventually appear white.

It is the dispersion of light, that is, the dependence of the refractive index on the frequency of the wave, that explains the beautiful phenomenon of nature - the rainbow (Fig. 4).

Rice. 4. The phenomenon of the rainbow ()

A rainbow occurs when sunlight is refracted and reflected by droplets of water, rain, or mist floating in the atmosphere. These droplets deflect light of different colors in different ways, as a result, the white color decomposes into a spectrum, that is, dispersion occurs, the observer, who stands with his back to the light source, sees a multi-colored glow that comes from space along concentric arcs.

Dispersion also explains the wonderful play of color on the facets of precious stones.

1. The phenomenon of dispersion is the decomposition of light into a spectrum, due to the dependence of the refractive index on the frequency of electromagnetic radiation, that is, the frequency of light. 2. Body color is determined by the body's ability to reflect or scatter one or another frequency of electromagnetic radiation.

Bibliography

1. Tikhomirova S.A., Yavorsky B.M. Physics (basic level) - M.: Mnemozina, 2012.
2. Gendenstein L.E., Dick Yu.I. Physics grade 10. - M.: Mnemosyne, 2014.
3. Kikoin I.K., Kikoin A.K. Physics - 9, Moscow, Education, 1990.

Homework

1. What conclusions did Newton draw from his experiment with a prism?
2. Define dispersion.
3. What determines body color?

1. Internet portal B-i-o-n.ru ().
2. Internet portal Sfiz.ru ().
3. Internet portal Femto.com.ua ().

The world around us is filled with millions of different shades. Due to the properties of light, every object and object around us has a certain color perceived by human vision. The study of light waves and their characteristics has allowed people to take a deeper look at the nature of light and the phenomena associated with it. Let's talk about dispersion today.

The nature of light

From a physical point of view, light is a combination of electromagnetic waves with different lengths and frequencies. The human eye does not perceive any light, but only one whose wavelength ranges from 380 to 760 nm. The rest of the varieties remain invisible to us. These include, for example, infrared and ultraviolet radiation. The famous scientist Isaac Newton imagined light as a directed stream of the smallest particles. And only later it was proved that it is by nature a wave. However, Newton was still partly right. The fact is that light has not only wave, but also corpuscular properties. This is confirmed by the well-known phenomenon of the photoelectric effect. It turns out that the light flux has a dual nature.

Color spectrum

White light accessible to human vision is a combination of several waves, each of which is characterized by a certain frequency and its own photon energy. In accordance with this, it can be decomposed into waves of different colors. Each of them is called monochromatic, and a certain color corresponds to its own range of length, wave frequency and photon energy. In other words, the energy emitted by a substance (or absorbed) is distributed according to the above indicators. This explains the existence of the light spectrum. For example, the green color of the spectrum corresponds to a frequency in the range from 530 to 600 THz, and violet - from 680 to 790 THz.

Each of us has ever seen how the rays shimmer on faceted glassware or, for example, on diamonds. This can be observed due to such a phenomenon as the dispersion of light. This is an effect that reflects the dependence of the refractive index of an object (substance, medium) on the length (frequency) of the light wave that passes through this object. The consequence of this dependence is the decomposition of the beam into a color spectrum, for example, when passing through a prism. The dispersion of light is expressed by the following equation:

where n is the refractive index, ƛ is the frequency, and ƒ is the wavelength. The refractive index increases with increasing frequency and decreasing wavelength. We often observe dispersion in nature. Its most beautiful manifestation is the rainbow, which is formed due to the scattering of the sun's rays when they pass through numerous raindrops.

The first steps towards the discovery of dispersion

As mentioned above, when passing through a prism, the light flux decomposes into a color spectrum, which Isaac Newton studied in sufficient detail in his time. The result of his research was the discovery of the phenomenon of dispersion in 1672. Scientific interest in the properties of light appeared even before our era. The famous Aristotle already then noticed that sunlight can have different shades. The scientist argued that the nature of the color depends on the "amount of darkness" present in the white light. If there is a lot of it, then a purple color appears, and if it is not enough, then red. The great thinker also said that the main color of light rays is white.

Studies of Newton's predecessors

The Aristotelian theory of the interaction of darkness and light was not refuted by scientists of the 16th and 17th centuries. Both the Czech researcher Marzi and the English physicist Khariot independently conducted experiments with a prism and were firmly convinced that the reason for the appearance of different shades of the spectrum is precisely the mixing of the light flux with darkness when it passes through the prism. At first glance, the conclusions of scientists could be called logical. But their experiments were rather superficial, and they could not back them up with additional research. That was until Isaac Newton took over.

Newton's discovery

Thanks to the inquisitive mind of this outstanding scientist, it was proved that white light is not the main one, and that other colors do not arise at all as a result of the interaction of light and darkness in different proportions. Newton refuted these beliefs and showed that white light is composite in its structure, it is formed by all the colors of the light spectrum, called monochromatic. As a result of the passage of a light beam through a prism, a variety of colors is formed due to the decomposition of white light into its constituent wave streams. Such waves with different frequencies and lengths are refracted in the medium in different ways, forming a certain color. Newton set up experiments that are still used in physics. For example, experiments with crossed prisms, using two prisms and a mirror, as well as passing light through prisms and a perforated screen. Now we know that the decomposition of light into a color spectrum occurs due to the different speeds of the passage of waves with different lengths and frequencies through a transparent substance. As a result, some waves leave the prism earlier, others a little later, still others later, and so on. This is how the decomposition of the light flux occurs.

Anomalous dispersion

In the future, physicists of the century before last made another discovery regarding dispersion. The Frenchman Leroux discovered that in some media (in particular, in iodine vapor) the dependence expressing the phenomenon of dispersion is violated. The physicist Kundt, who lived in Germany, took up the study of this issue. For his research, he borrowed one of Newton's methods, namely the experiment using two crossed prisms. The only difference was that instead of one of them, Kundt used a prismatic vessel with a solution of cyanine. It turned out that the refractive index when light passes through such prisms increases rather than decreases, as happened in Newton's experiments with conventional prisms. The German scientist found out that this paradox is observed due to such a phenomenon as the absorption of light by matter. In the experiment described by Kundt, the absorbing medium was a solution of cyanine, and the dispersion of light for such cases was called anomalous. In modern physics, this term is practically not used. Today, the normal dispersion discovered by Newton and the anomalous dispersion discovered later are considered as two phenomena related to the same doctrine and having a common nature.

Low Dispersion Lenses

In photography, light dispersion is considered an undesirable phenomenon. It causes the so-called chromatic aberration, in which colors appear distorted in images. The hues of the photograph do not match the hues of the subject being photographed. This effect becomes especially unpleasant for professional photographers. Due to the dispersion in the photographs, not only the colors are distorted, but the edges are often blurred or, conversely, the appearance of an overly defined border. Global photo equipment manufacturers cope with the consequences of such an optical phenomenon with the help of specially designed low dispersion lenses. The glass from which they are made has an excellent property to equally refract waves with different values ​​of length and frequency. Objectives with low dispersion lenses are called achromats.