The world filled with millions of different shades. Thanks to the properties of light, every object and object around us has a certain color, perceived 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. Today we'll talk about variance.

Nature of light

WITH physical point light is a combination of electromagnetic waves With different meanings length and frequency. The human eye does not perceive any light, but only that whose wavelength ranges from 380 to 760 nm. The remaining 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 most fine particles. It was only later that it was proven that it is a wave in nature. 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 luminous 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 energy of photons. Accordingly, it can be divided 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 frequencies ranging from 530 to 600 THz, and violet from 680 to 790 THz.

Each of us has ever seen how rays shimmer on cut glass products or, for example, on diamonds. This can be observed due to a phenomenon called light dispersion. 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. Light dispersion is expressed by the following equality:

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 sunlight as it passes through numerous raindrops.

The first steps towards the discovery of variance

As mentioned above, the luminous flux, when passing through a prism, is decomposed 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 before our era. The famous Aristotle already noticed that sunlight can have different shades. The scientist argued that the nature of color depends on the "amount of darkness" present in white light. If there is a lot of it, then a purple color appears, and if there is little, then red. Great thinker also said that the main color of light rays is white.

Research into Newton's predecessors

Aristotle's 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 Hariot independently conducted experiments with a prism and were firmly convinced that the reason for the appearance of different shades of the spectrum was precisely the mixing of the light flux with darkness when passing through the prism. At first glance, the scientists' conclusions could be called logical. But their experiments were rather superficial, and they were unable to back them up with additional research. That was until Isaac Newton got down to business.

Newton's discovery

Thanks to the inquisitive mind of this outstanding scientist, it was proven 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 ratios. 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 are 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 performed experiments that are still used in physics today. For example, experiments with crossed prisms, using two prisms and a mirror, and passing light through prisms and a perforated screen. We now know that the decomposition of light into a color spectrum occurs due to the different speeds at which waves of different lengths and frequencies pass through a transparent substance. As a result, some waves leave the prism earlier, others a little later, others even later, and so on. This is how the light flux decomposes.

Anomalous dispersion

Subsequently, 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 an experiment using two crossed prisms. The only difference was that instead of one of them, Kundt used a prismatic vessel with a cyanine solution. It turned out that the refractive index when light passes through such prisms increases, and does not decrease, as happened in Newton's experiments with ordinary prisms. The German scientist found that this paradox is observed due to a phenomenon such as the absorption of light by matter. In the described Kundt experiment, the absorbing medium was a cyanine solution, 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 photographic technology, light dispersion is considered an undesirable phenomenon. It causes so-called chromatic aberration, in which colors appear distorted in images. The shades of the photograph do not match the shades of the subject being photographed. This effect becomes especially unpleasant for professional photographers. Due to dispersion in photographs, not only colors are distorted, but edges are often blurred or, conversely, an overly defined border appears. Global photographic equipment manufacturers are coping with the consequences of this optical phenomenon using specially designed low dispersion lenses. The glass from which they are made has the excellent property of refracting waves of different lengths and frequencies equally. Lenses in which low-dispersion lenses are installed are called achromats.

Lesson objectives:

• Educational:
  • introduce the concepts of spectrum, light dispersion;
  • To acquaint students with the history of the discovery of this phenomenon.
  • clearly demonstrate the process of decomposition of a narrow light beam into components of various color shades.
  • identify the differences between these elements of the light beam.
  • continue to form the scientific worldview of students.
• Developmental:
  • development of attention, imaginative and logical thinking, memory when studying this topic.
  • stimulating cognitive motivation of students.
  • development of critical thinking.
• Educational:
  • nurturing interest in the subject;
  • nurturing a sense of beauty, the beauty of the surrounding world.

Lesson type: a lesson in studying and initially consolidating new knowledge.

Teaching methods: conversation, story, explanation, experiment. (Information and development)

Requirements to basic level preparation: be able to describe and explain the phenomenon of dispersion.

Equipment and materials: computer, color cards, plane-parallel plates

Lesson plan:

	Lesson steps	Time, min	Techniques and methods
1.	Color painting	5 min. (before class, during recess)	Choosing a color card that matches the mood for each student before class during recess.
2.	Motivation	2 minutes.	Teacher's story
3.	Organizational moment	3 min.	Reading a poem by a student
4.	Learning new material	19 min.	Teacher's story. Demonstration of experiments. Conversation on issues. Notes in notebooks.
5.	Consolidation Sinkwine	12 min.	Teacher consultation. Observation. Student answers. Compiling a syncwine
6.	Summarizing. Color painting	3 min.	Summarizing the material studied. Each student selects a color card to match their mood at the end of the lesson.
7.	Homework	1 min.	Writing on the board. Teacher's comment.

Before the start of the lesson, during recess, conduct the “Class Color Design” diagnostic. Each student, entering the classroom, chooses a card with a certain color that matches his mood, and a “Class Color Chart” is drawn up at the beginning of the lesson.

• Yellow color is good
• Orange – very good
• Red – joyful
• Green – calm
• Blue – sad
• Brown – alarming
• Black – bad
• White – indifferent

Epigraph for the lesson:

Nature cannot be caught sloppy and half-naked; she is always beautiful.

R. Emerson (American philosopher of the 19th century)

DURING THE CLASSES

1. Motivation

Sunlight has always been and remains for a person a symbol of joy, eternal youth, all the good, the best that can be in life:

“Let there always be the Sun.
May there always be heaven..." -

Such words are in the famous song written by Lev Oshanin.
Even a physicist. Accustomed to dealing with facts, with accurate registration of phenomena, sometimes feels awkward when saying that light is electromagnetic waves of a certain wavelength and nothing more.
The wavelength of light is very short. Imagine the average sea ​​wave, which would increase so much that it would occupy the entire Atlantic Ocean alone - from America to Lisbon in Europe. The wavelength of light at the same magnification would only slightly exceed the width of a book page.
Question:
– Where do these electromagnetic waves come from?
Answer:
– Their source is the Sun.
Along with visible radiation, the Sun sends us thermal radiation, infrared and ultraviolet. Heat The sun is the main cause of the birth of these electromagnetic waves.

2. Organizational moment

Formulation of the topic and objectives of the lesson.

The topic of our lesson is “Dispersion of Light”. Today we need:

• Introduce the concept of “spectrum”, “dispersion of light”;
• Identify the features of this phenomenon - light dispersion;
• Get acquainted with the history of the discovery of this phenomenon.

Activation of mental activity:

A student reads a poem

Scent of the Sun

The smell of the sun? What nonsense!
No, not nonsense.
Sounds and dreams in the sun,
Fragrances and flowers,
Everyone merged into a consonant chorus,
Everything is woven into one pattern.
The sun smells like herbs,
Fresh baths,
In the awakening spring
And resinous pine,
Delicately light woven
Drunk with lilies of the valley,
What bloomed victoriously
In the pungent smell of earth.
The sun is shining with bells,
Green leaves
Breathes outside singing birds,
Breathe with the laughter of young faces.
So say this to all the blind:
It will be for you!
You will not see the gates of heaven,
The sun has a scent
Sweetly intelligible only to us,
Visible to birds and flowers!
A. Balmont

3. Learning new material

A little history

Speaking about these ideas, we should start with Aristotle’s color theory (IV century BC). Aristotle argued that the difference in color is determined by the difference in the amount of darkness “mixed” with sunlight (white) light. Violet color, according to Aristotle, arises 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 in observing the decomposition of light by prisms did not give rise to doubts about the correctness of Aristotle’s theory of the appearance of colors. Both Hariot and Marzi remained followers of this theory. This should not be surprising, since at first glance the decomposition of light by a prism into various colors seemed to confirm the idea that color arises as a result of the mixing of light and darkness. The rainbow stripe appears precisely at the transition from the shadow stripe to the illuminated stripe, that is, at the border of darkness and white light. From the fact that the violet ray travels the longest path 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 to white light occurs. It was not difficult to prove the falsity of such conclusions by performing corresponding experiments with the same prisms. However, no one had done this before Newton.

Sunlight has many secrets. One of them - dispersion phenomenon. The great English physicist was the first to discover it Isaac Newton in 1666 while improving the telescope.

Light dispersion(decomposition of light) is a phenomenon caused by the dependence of the absolute refractive index of a substance on the frequency (or wavelength) of light (frequency dispersion), or, the same thing, the dependence of the phase speed of light in a substance on the wavelength (or frequency).

The dispersion of light was discovered experimentally by I. Newton around 1672, although theoretically it was quite well explained much later.
One of the most illustrative examples dispersion - the decomposition of white light when passing through a prism (Newton's experiment). The essence of the dispersion phenomenon is the unequal speed of propagation of light rays with different wavelengths in a transparent substance - an optical medium (while in a vacuum the speed of light is always the same, regardless of the wavelength and therefore color). Typically, the higher the frequency of the wave, the higher the refractive index of the medium and the lower its speed of light in it:

• in red maximum speed in the medium and the minimum degree of refraction,
• at purple the minimum speed of light in a medium and the maximum degree of refraction.

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

White light is decomposed into a spectrum as a result of passing through a diffraction grating or reflection 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; normal (diffraction) spectrum is uniform in all areas and is arranged in order of increasing wavelengths: from violet to red.

Knowing that white light has a complex structure, we can explain the amazing variety of colors in nature. If an object, such as a sheet of paper, reflects all the rays of different colors falling on it, then it will appear white. By covering the paper with a layer of red paint, we do not create a new color of light, but retain some of the existing light on the sheet. Now only red rays will be reflected, the rest will be absorbed by the paint layer. Grass and tree leaves appear green to us because of all the sun's rays falling on them, they reflect only green ones, absorbing the rest. If you look at the grass through red glass, which transmits only red rays, it will appear almost black.

The phenomenon of dispersion, discovered by Newton, is the first step towards understanding the nature of color. The depth of understanding of dispersion came after the dependence of color on the frequency (or wavelength) of light was clarified.

Thomas Young (1773-1829) was the first to measure the wavelengths of different colors in 1802.

After the discovery of light dispersion, the wavelength became the main quantity determining the color of light. The main color receptor is the retina of the eye.

Color- there is a sensation that occurs in the retina of the eye when it is excited by a light wave of a certain length. Knowing the wavelength of the emitted light and the conditions of its propagation, it is possible to predict in advance with a high degree of accuracy what color the eye will see.

It may be that the retina of the eye perceives one of the primary colors poorly or does not react to it at all, then this person’s color perception is impaired. This type of vision deficiency is called color blindness.

Good color perception is very important for a number of professions: sailors, pilots, railway workers, surgeons, artists. Special devices have been created - anomaloscopes for the study of color vision disorders.

Dispersion explains the fact that a rainbow appears after rain (more precisely, the fact that the rainbow is multi-colored and not white).
First attempt to explain rainbow as a natural phenomenon was made in 1611 by Archbishop Antonio Dominis.

1637 – scientific explanation Rainbows were first given by Rene Descartes. He explained the rainbow based on the laws of refraction and reflection sunlight in the raindrops. The phenomenon of dispersion had not yet been discovered, which is why Descartes' rainbow turned out to be white.

30 years later Isaac Newton complemented Descartes' theory and explained how colored rays are refracted in raindrops.

“Descartes hung the rainbow in the right place in the sky, and Newton colored it with all the colors of the spectrum.”

American scientist A. Fraser

Rainbow is an optical phenomenon associated with the refraction of light rays by numerous raindrops. However, not everyone knows exactly how the refraction of light on raindrops leads to the appearance of a giant multicolored arc in the sky. Therefore, it is useful to dwell in more detail on the physical explanation of this spectacular optical phenomenon.

Rainbow through the eyes of an attentive observer. First of all, a rainbow can only be observed in the direction opposite to the Sun. If you stand facing the rainbow, the Sun will be behind you. A rainbow occurs when the Sun illuminates a curtain of rain. As the rain subsides and then stops, the rainbow fades and gradually disappears. The colors observed in a rainbow alternate in the same sequence as in the spectrum obtained by passing a beam of sunlight through a prism. In this case, the inner (facing the Earth's surface) extreme region of the rainbow is colored violet, and the outer extreme region is red. Often, another (secondary) rainbow appears above the main rainbow - wider and blurrier. The colors in the secondary rainbow alternate in reverse order: from red (extreme inner area arc) to violet (outermost region).

For an observer standing on relatively flat earth's surface, a rainbow appears provided that the angular height of the Sun above the horizon does not exceed approximately 42°. The lower the Sun, the greater the angular height of the top of the rainbow and, therefore, the larger the observed portion of the rainbow. A secondary rainbow can be observed if the height of the Sun above the horizon does not exceed approximately 52.

The rainbow can be considered as a giant wheel, which, like an axle, is mounted on an imaginary straight line passing through the Sun and the observer.

Dispersion is the cause of chromatic aberrations - one of the aberrations of optical systems, including photographic and video lenses.

Dispersion of light in nature and art

• Due to dispersion it can be observed different colors Sveta.
• The rainbow, whose colors are due to dispersion, is one of the key images of culture and art.
• Thanks to light dispersion, it is possible to observe the colored “play of light” on the facets of a diamond and other transparent faceted objects or materials.
• To one degree or another, rainbow effects are found quite often when light passes through almost any transparent object. In art they can be specifically intensified and emphasized.
• The decomposition of light into a spectrum (due to dispersion) when refracted in a prism is a fairly common topic in fine arts. For example, the cover of the album Dark Side Of The Moon by Pink Floyd depicts the refraction of light in a prism with decomposition into a spectrum.

The discovery of dispersion was very significant in the history of science. On the scientist’s tombstone there is an inscription with the following words: “Here lies Sir Isaac Newton, the nobleman who ... was the first with the torch of mathematics to explain the movements of the planets, the paths of comets and the tides of the oceans.

He investigated the difference in light rays and the various properties of colors that appear in this process, which no one had previously suspected. …Let mortals rejoice that such an adornment of the human race existed.”

4. Consolidation

• Answer questions on the topic studied.
• Category "Think..."
• Question: Why is the rainbow round?
• Compilation of “Sinquain” on the topic “Variance”

5. Summing up the lesson

At the end of the lesson, conduct the “Class Coloring” diagnostic again. Find out what the mood was at the end of the lesson, on the basis of which a “Class Coloring” diagram is drawn up and the result is compared, what mood the students were at the beginning of the lesson and at the end.

6. Homework:§66

Literature:

1. Myakishev G.Ya., Bukhovtsev B.B. Physics: Textbook for 11th grade of high school. – M.: Education, 2006.
2. Rymkevich A.P. Collection of problems in physics for grades 9-11 of high school. – M.: Education, 2006.
3. Reader on physics: Tutorial for students in grades 8-10 of secondary school / Ed. B.I.
4. Spassky. – M.: Education, 1987.

Journal "Physics at School" No. 1/1998

Nature of light

The world around us is filled with millions of different shades. Thanks 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. Today we'll talk about variance. 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 that whose wavelength ranges from 380 to 760 nm. The remaining varieties remain invisible to us. These include, for example, infrared and ultraviolet radiation

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. The famous scientist Isaac Newton imagined light as a directed stream of tiny particles. It was only later that it was proven that it is a wave in nature. However, Newton was still partly right. The fact is that light has not only wave, but also corpuscular...

Light dispersion (light decomposition) is a phenomenon caused by the dependence of the absolute refractive index of a substance on the frequency (or wavelength) of light (frequency dispersion), or, the same thing, the dependence of the phase speed of light in a substance on the wavelength (or frequency) . It was discovered experimentally by Newton around 1672, although theoretically quite well explained much later.

One of the most obvious examples of dispersion is the decomposition of white light when passing through a prism (Newton's experiment). The essence of the dispersion phenomenon is the unequal speed of propagation of light rays with different wavelengths in a transparent substance - an optical medium (while in a vacuum the speed of light is always the same, regardless of the wavelength and therefore color). Typically, the higher the frequency of the wave, the higher the refractive index...

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Newton's experiments

Newton made the first experiments with the dispersive decomposition of light. He directed an ordinary beam of sunlight onto a prism and got what many today see every day - the prism split the light beam into many different colors - from red to violet. After a series of other experiments with lenses and prisms, Newton concluded that a prism does not change sunlight, but only decomposes it into its components. But how does this happen?

The fact is that light has a certain speed. As experience has shown, a light beam consists of many colors, and it is their speed that is different. That is, each color of the spectrum has its own speed of movement and its own wavelength. The degree of refraction of color rays also turned out to be different. Remember what it looks like...

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Chapter 1. Light Waves - Lesson 5. Dispersion of Light
Return to contents
Lesson 5. DISPERSION OF LIGHT

The refractive index does not depend on the angle of incidence of the light beam, but it depends on its color. This was discovered by Newton.

Improving telescopes. Newton noticed this. that the image produced by the lens is colored at the edges. He became interested in this and was the first to “investigate the variety of light rays and the resulting characteristics of colors, which no one had even suspected before” (words from the inscription on tombstone Newton). The rainbow coloring of the image produced by the lens had, of course, been observed before him. It has also been observed that rainbow edges have objects viewed through a prism. A beam of light rays passing through a prism is colored along the edges.

Newton's basic experiment was brilliantly simple. Newton guessed to direct a light beam of small cross-section to a prism. A beam of sunlight passed into a darkened...

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Gymnasium No. 26 DISPERSION OF LIGHT Completed by: student of class 11 B Shelepov Dmitry Supervisor: Pylkova L.V. Tomsk-2011 In the 17th century, the idea of ​​the wave nature of light began to develop. The first discovery indicating the wave nature of light was made by the Italian scientist Francesco Grimaldi. He noticed that if an object is placed in the path of a very narrow beam of light, then a sharp shadow does not appear on the screen. The edges of the shadow are blurred and streaks of color appear along the shadow. Grimaldi called the discovered phenomenon diffraction, but failed to explain it correctly. He understood that the phenomenon he observed was in conflict with the corpuscular theory of light, but did not dare to completely abandon this theory. Correct explanation open phenomenon associated with the theory of color vision, the foundations of which were laid by the remarkable English scientist Isaac Newton. Light dispersion (light decomposition) is the phenomenon of the dependence of the absolute refractive index of a substance on the wavelength of light...

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Light dispersion (light decomposition) is the 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, which is the same, the dependence of the phase speed of light in a substance on the length waves (or frequencies). It was discovered experimentally by Newton around 1672, although theoretically quite well explained much later.

One of the most obvious examples of dispersion is the decomposition of white light when passing through a prism (Newton's experiment). The essence of the dispersion phenomenon is the unequal speed of propagation of light rays with different wavelengths in a transparent substance - an optical medium (while in a vacuum the speed of light is always the same, regardless of wavelength and therefore color). Typically, 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 has the maximum speed in the medium and the minimum degree of refraction,...

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Physics lesson "Dispersion of light"

Sections: Physics

Lesson objectives:

Educational: introduce the concepts of spectrum, light dispersion; To acquaint students with the history of the discovery of this phenomenon. clearly demonstrate the process of decomposition of a narrow light beam into components of various color shades. identify the differences between these elements of the light beam. continue formation scientific worldview students. Developmental: development of attention, figurative and logical thinking, memory when studying this topic. stimulating cognitive motivation of students. development of critical thinking. Educational: fostering interest in the subject; nurturing a sense of beauty, the beauty of the surrounding world.

Lesson type: lesson on studying and initially consolidating new knowledge.

Teaching methods: conversation, story, explanation, experiment. (Information and development)

Requirements to...

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Ministry of Science and Education of Ukraine

Ukrainian Engineering and Pedagogical Academy

Report on the topic:

Light dispersion

Completed by student gr. DRE-S5-1

Fesenko A.V.

Kharkov 2006

Dispersion phenomenon

Dispersion of light. On a bright sunny day, we close the window in the room with a thick curtain, in which we make a small hole. Through this hole a narrow ray of sunlight will penetrate into the room, forming a light spot on the opposite wall. If you put in the path of the beam

glass prism, then the spot on the wall will turn into a multi-colored strip, in which all the colors of the arc will be represented - from violet to red (Fig. 1, f - violet, C - blue, G - blue, 3 - green, F - yellow , O - orange, K - red).

Light dispersion is the dependence of the refractive index n of a substance on the frequency f (wavelength) of light or the dependence...

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Slide 1
The word “variance” comes from Latin word dispersio, which literally means “scattering, dispersal”. Dispersion of light The work was carried out by a student of class 11 “E” Adelshina Ilvira

Slide 2
History of discovery Definition Newton's experiment Feature of the passage of a light beam through a prism Main properties Consequences Conditions for the appearance of a rainbow Questions Conclusions Contents

Slide 3
When passing through a prism, a luminous flux is decomposed 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. The first steps towards the discovery of variance

Slide 4
About 300 years ago Isaac Newton missed Sun rays through the prism. It is not for nothing that on his tombstone, erected in 1731 and decorated with figures of young men who hold in their hands the emblems of his most important discoveries, one figure holds a prism, and the inscription on the monument contains the words: “He...

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10

Studying light dispersion in 11th grade

Tishkova Svetlana Anatolyevna, physics teacher

The article belongs to the section: Teaching physics

This lesson is taught at the end of studying the topic “wave properties of light” in physics and mathematics classes.

A. Students must learn:

A beam of white light, when passing through a substance having a refractive angle, is decomposed into beams of different colors. This phenomenon is called light dispersion.

When falling on the interface between two media, light beams of different colors are refracted differently: red ones - less, and violet - more.

An objective characteristic of color is the frequency of an electromagnetic wave.

B. Students should learn:

Create the concept of “dispersion of light”.

Recognize light dispersion among other phenomena.

Reproduce light dispersion in a specific situation.

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11

Dispersion of light is considered as a result of the interaction of electromagnetic waves with charged particles that are part of substances. Particles of matter perform forced oscillations in the alternating electromagnetic field of the wave.

Light dispersion is the dependence of the absolute refractive index of a substance n on frequency...

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12

Observation of the phenomenon of light dispersion laboratory
In physics, light dispersion is the dependence of the refractive index of a substance on the wavelength of light. The phenomenon of light dispersion is most clearly demonstrated by its decomposition under the influence of some kind of prism.

1.3. First experiments with prisms. Ideas about the origins of colors before Newton.
1.4. Newton's experiments with prisms. Newton's theory of the origin of colors
1.5. Discovery of anomalous dispersion of light. Kundt's experiments
Chapter II. Dispersion in nature
2.1. Rainbow
Chapter III. Experimental setup for observing color mixing
3.1. Description of installation
3.2. Experimental setup
Conclusion
Literature
Introduction.
Dispersion of light. We always come across this phenomenon in life, but we don’t always notice it. But if you are careful, the phenomenon of dispersion always surrounds us. One such phenomenon is an ordinary rainbow. There is probably no person who doesn't...

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13

MAOU " high school No. 28 named after G. F. Kirdishchev"

Petropavlovsk-Kamchatsky urban district

Dispersion of light and color of bodies

Physics lesson notes in 11th grade

Lesson of learning new material, consolidation and control

Physics teacher of MAOU “Secondary School No. 28 named after G. F. Kirdishchev” Yuryeva O. L.

Sergey Yesenin

I do not regret, do not call, do not cry,
Everything will pass like smoke from white apple trees.
Withered in gold,
I won't be young anymore.

Now you won't fight so much,
A heart touched by a chill,
And the country of birch chintz
It won't tempt you to wander around barefoot.

The wandering spirit! you are less and less often
You stir up the flame of your lips
Oh my lost freshness
A riot of eyes and a flood of feelings!

I have now become more stingy in my desires,
My life, did I dream about you?
As if I were a booming early spring
He rode on a pink horse.

All of us, all of us in this world are perishable,
It flows quietly...

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14

What waves are called coherent?

waves having the same frequency

waves having the same amplitude

waves having the same frequency and constant phase difference

Polarization of light proves that light is
neutral particle flux
transverse wave
longitudinal waves

What is diffraction of light?
decomposition of white light into a spectrum using a glass prism
amplification or attenuation of light when two coherent waves are superimposed
bending light around obstacles

The colors of the spectrum (red - k, orange - o, blue - s, yellow - g, blue - g, green - z, violet - f) in order of decreasing wavelength are correctly indicated in the answer:
1.f, s, g, z, g, o, k
k, o, g, h, g, s, f
f, g, h, s, g, o, k

The rainbow coloring of thin films of petroleum products in puddles is caused by the phenomenon
diffraction
variances
interference

The clearing of the lenses is explained by...

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15

Abstract: Lesson topic: “Light is a stream of particles”
Teacher Pylkova L.V., Municipal Educational Institution Gymnasium No. 26

Lesson topic: “Light is a stream of particles”

Lesson Type: Modified Debate

The organization of "modified" debates allows for some changes in the rules; the number of players in teams can be increased or decreased; Questions from the audience are acceptable, support groups are organized that teams can contact during the game, a group of experts performs refereeing functions, and develops a compromise solution when necessary to achieve educational goals. The main stages of the organization educational process based on the use of debate techniques are: orientation (choice of topic); preparation for the event; holding debates; discussion of the game.

^Lesson objectives:

Generalization and systematization of knowledge

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

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

Encyclopedic YouTube

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Dispersion and spectrum of light

Light Dispersion and Body Color

Dispersion of light. Body colors

Subtitles

Properties and manifestations

One of the most obvious examples of dispersion is the decomposition of white light when passing through a prism (Newton's experiment). The essence of the dispersion phenomenon is the difference in the phase speeds of propagation of light rays of different wavelengths in a transparent substance - an optical medium (while in a vacuum the speed of light is always the same, regardless of the wavelength and therefore color). Typically, the shorter the light wavelength, the greater the refractive index of the medium for it and the lower the phase speed of the wave in the medium:

• red light has a maximum phase speed of propagation in the medium and a minimum degree of refraction,
• For violet light, the phase speed of propagation in the medium is minimal, and the degree of refraction is maximum.

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

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

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

n = a + b / λ 2 + c / λ 4 (\displaystyle n=a+b/\lambda ^(2)+c/\lambda ^(4)),

Where λ (\displaystyle \lambda)- wavelength in vacuum; a, b, c- constants, the values ​​of which for each material must be determined experimentally. In most cases, you can limit 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.

3. Free vibrations in the lc circuit. Free damped oscillations. Differential equation of damped oscillations and its solution.

4. Forced electrical oscillations. Differential equation of forced oscillations and its solution.

5. Voltage resonance and current resonance.

Fundamentals of Maxwell's theory for the electromagnetic field.

6. General characteristics of Maxwell's theory. Vortex magnetic field. Bias current.

7.Maxwell's equations in integral form.

Electromagnetic waves

8. Experimental production of electromagnetic waves. Plane electromagnetic wave. Wave equation for the electromagnetic field. Energy of electromagnetic waves. Pressure of electromagnetic waves.

Geometric optics

9. Basic laws of geometric optics. Photometric quantities and their units.

10. Refraction of light on spherical surfaces. Thin lenses. The formula for a thin lens and the construction of images of objects using a thin lens.

11. Light waves

12.Interference of light when reflected from thin plates. Strips of equal thickness and equal slope.

13. Newton's rings. Application of the interference phenomenon. Interferometers. Enlightening optics.

14.Diffraction of light

15. Diffraction of light on a round screen and a round hole.

16.Diffraction of light by one slit. Diffraction grating.

17. 18. Interaction of light with matter. Dispersion and absorption of light. Normal and anomalous dispersion. Bouguer-Lambert law.

19.Polarization of light. Natural and polarized light. Degree of polarization. Malus's law.

20. Polarization of light during reflection and refraction. Brewster's Law. Birefringence. Anisotropy of crystals.

21. Doppler effect for light waves.

22. Thermal radiation. Properties of equilibrium thermal radiation. Absolutely black body. Energy distribution in the spectrum of a completely black body. Laws of Kirchhoff, Stefan-Boltzmann, Wien.

23. Elements of the special theory of relativity Postulates of the special theory of relativity. Lorentz transformations.

2. Duration of events in different reference systems.

24. Basic laws of relativistic dynamics. The law of the relationship between mass and energy.

17. 18. Interaction of light with matter. Dispersion and absorption of light. Normal and anomalous dispersion. Bouguer-Lambert law.

Light dispersion call the phenomenon of dependence of the absolute refractive index of a substance n on the frequency of light ω (or wavelength λ):

The consequence of light dispersion is the decomposition into a spectrum of a beam of white light when passing through a prism. The first experimental study of light dispersion in a glass prism was carried out by I. Newton in 1672.

Light dispersion called normal if the refractive index increases monotonically with increasing frequency (decreases with increasing wavelength); otherwise the variance is called abnormal, Fig.1.

Magnitude

called dispersion of matter and characterizes the rate of change in the refractive index with a change in wavelength.

Normal dispersion of light is observed far from the bands or lines of absorption of light by a substance, anomalous - within the bands or lines of absorption.

Let's consider the dispersion of light in a prism, Fig. 2.

Let a monochromatic beam of light fall on a transparent prism with a refractive angle θ and refractive index n at an angle α 1. After a double deflection (on the left and right faces of the prism), the beam turns out to be deviated from the original direction by an angle φ. From geometric transformations it follows that

those. The angle of deflection of rays by a prism is greater, the greater the refractive angle and the refractive index of the prism substance. Since n = f(λ), then the rays different lengths waves after passing the prism will be deflected at different angles, i.e. a beam of white light incident on a prism, behind the prism, is decomposed into a spectrum, which was first observed by Newton. This means that with the help of a prism, as well as with the help of a diffraction grating, by decomposing light into a spectrum, it is possible to determine its spectral composition.

It should be remembered that the component colors in the diffraction and prismatic spectra are located differently. In the diffraction spectrum, the sine of the deflection angle is proportional to the wavelength, therefore, red rays having longer length waves are deflected more strongly by the diffraction grating than violet ones. In a prism, for all transparent substances with normal dispersion, the refractive index n decreases with increasing wavelength, so red rays are deflected by the prism less than violet rays.

On the Appearance normal dispersion action based prism spectrometers, widely used in spectral analysis. This is explained by the fact that it is much easier to make a prism than a diffraction grating. Prism spectrometers also have a high aperture ratio.

Electronic theory of light dispersion. From Maxwell's macroscopic electromagnetic theory it follows that

but in the optical region of the spectrum for all substances μ ≈ 1, therefore

n= ε. (1)

Formula (1) contradicts experience, because the quantity n, being a variable n = f(λ), is at the same time equal to a certain constant ε (constant in Maxwell's theory). In addition, the values ​​of n obtained from this expression do not agree with the experimental data.

To explain the dispersion of light, it was proposed electronic Lorentz theory, in which the dispersion of light is considered as a result of the interaction of electromagnetic waves with charged particles that are part of the substance and perform forced oscillations in the alternating electromagnetic field of the wave.

Let's get acquainted with this theory using the example of a homogeneous isotropic dielectric, formally assuming that the dispersion of light is a consequence of the dependence of ε on the frequency ω of light waves. The dielectric constant of the substance is

ε = 1 + χ = 1 + P/(ε 0 E),

where χ is the dielectric susceptibility of the medium, ε 0 is the electrical constant, P is the instantaneous value of polarization (induced dipole moment per unit volume of the dielectric in the wave field of intensity E). Then

n 2 = 1 + P/(ε 0 E), (2)

those. depends on R. For visible light the frequency ω~10 15 Hz is so high that only forced vibrations of the external (most weakly bound) electrons of atoms, molecules or ions under the influence of the electric component of the wave field are significant, and there will be no orientational polarization of molecules at such a frequency. These electrons are called optical electrons.

For simplicity, let us consider the vibrations of one optical electron in a molecule. The induced dipole moment of an electron performing forced oscillations is equal to p = ex, where e is the charge of the electron, x is the displacement of the electron from the equilibrium position under the influence of the electric field of the light wave. Let n 0 be the concentration of atoms in the dielectric, then

P = p n 0 = n 0 e x. (3)

Substituting (3) into (2) we get

n 2 = 1 + n 0 e x /(ε 0 E), (4)

those. the problem comes down to determining the displacement x of the electron under the influence of an external electric field E = E 0 cos ωt.

Equation of forced oscillations of an electron for the simplest case

d 2 x/dt 2 +ω 0 2 x = (F 0 /m)cos ωt = (e/ m) E 0 cos ωt, (5)

where F 0 = еE 0 is the amplitude value of the force acting on the electron from the wave field, ω 0 = √k/m is the natural frequency of electron oscillations, m is the mass of the electron. Having solved equation (5), we find ε = n 2 depending on the atomic constants (e, m, ω 0) and the frequency of the external field ω, i.e. Let's solve the dispersion problem.

The solution to (5) is

Х = А cos ωt, (6)

A = eE 0 /m(ω 0 2 – ω 2). (7)

Substitute (6) and (7) into (4) and get

n 2 = 1 + n 0 e 2 /ε 0 m(ω 0 2 – ω 2). (8)

From (8) it is clear that the refractive index of a substance depends on the frequency ω of the external field, and that in the frequency range from ω = 0 to ω = ω 0 the value of n 2 is greater than 1 and increases with increasing frequency ω ( normal variance). At ω = ω 0 the value n 2 = ± ∞; in the frequency range from ω = ω 0 to ω = ∞, the value of n 2 is less than 1 and increases from - ∞ to 1 (normal dispersion). Moving from n 2 to n, we obtain a graph of n = n(ω), Fig. 1. Area AB – area anomalous dispersion. Study of anomalous dispersion – D.S. Christmas.

Absorption of light– is called a decrease in the energy of a light wave during its propagation in matter due to the conversion of wave energy into other types of energy.

From the point of view of electronic theory, the interaction of light and matter is reduced to the interaction of the electromagnetic field of a light wave with atoms and molecules of matter. The electrons that make up atoms can vibrate under the influence of the alternating electric field of a light wave. Part of the energy of the light wave is spent on exciting electron oscillations. Partially, the energy of electron oscillations again turns into the energy of light radiation, and also turns into other forms of energy, for example, into the energy of thermal radiation.

The absorption of light radiation can be described in general terms from an energy point of view, without going into details of the mechanism of interaction of light waves with atoms and molecules of the absorbing substance.

A formal description of the absorption of light by matter has been given Booger, who established a relationship between the intensity of light passing through a final layer of absorbing substance and the intensity of light incident on it

I lλ = I 0λ e -K l (1)

where I 0 λ is the intensity of light radiation with wavelength λ incident on the absorbing layer; I lλ- intensity of light radiation passing through an absorbing layer of substance thick l; K λ – absorption coefficient depending on λ, i.e. K λ = f(λ).

If the absorber is a substance in solution, then the absorption of light is greater, the more molecules of the dissolved substance the light encounters on its path. Therefore, the absorption coefficient depends on the concentration C. In the case of weak solutions, when the interaction of the molecules of the solute can be neglected, the absorption coefficient is proportional to C:

К λ = c λ С (2)

where c λ is the proportionality coefficient, which also depends on λ. Taking into account (2), Bouguer’s law (1) can be rewritten as:

I λ = I 0λ e - c C l (3)

c λ is the indicator of light absorption per unit concentration of the substance. If the concentration of a solute is expressed in [mol/liter], then c λ is called molar absorption coefficient.

Relationship (3) is called the Bouguer-Lambert-Beer law. Ratio of the magnitude of the luminous flux emerging from layer I lλ, to the entered I 0λ is called coefficient of optical (or light) transmittance of the layer T:

T = I lλ/I 0 λ = e - c C l (4)

or as a percentage

T = I lλ/I 0λ 100%. (5)

The absorption of the layer is equal to the ratio

L
the ogarithm of the value 1/T is called layer optical density D

D = log 1/T = log I 0 λ /I l λ = 0.43c λ C l (6)

those. Optical density characterizes the absorption of light by a medium. Relation (6) can be used both to determine the concentration of solutions and to characterize the absorption spectra of substances.

The dependence of optical density on wavelength D = f(λ) is a spectral characteristic of the absorption of a given substance, and the curve expressing this dependence is called absorption spectrum. Absorption spectra, like emission spectra, can be lined, striped and continuous, Fig. 3. According to the Bohr atomic model, light quanta are emitted and absorbed during the transition of a system (atom) from one energy state to another. If in this case only the electronic energy of the system changes in optical transitions, as is the case in atoms, then the absorption line in the spectrum will be sharp.

Fig. 3.a) line absorption spectrum, b) striped absorption spectrum, c) continuous absorption spectrum.

However, for complex molecules, the energy of which is composed of electronic E el, vibrational E coll and rotational E vr energy (E = E el + E coll + E vr), when light is absorbed, not only the electronic energy changes, but also the vibrational and rotational energy. Moreover, since ∆E el >>∆E count >>∆E vr, as a result of this, the set of lines corresponding to the electronic transition in the absorption spectrum of solutions looks like an absorption band.

The absorption coefficient for dielectrics is small (approximately 10 -3 – 10 -5 cm -1), wide absorption bands are observed for them, i.e. dielectrics have a continuous absorption spectrum. This is due to the fact that there are no free electrons in dielectrics and the absorption of light is due to the phenomenon of resonance forced vibrations electrons in atoms and atoms in dielectric molecules.

The absorption coefficient for metals has large values ​​(approximately 10 3 - 10 5 cm -1) and therefore metals are opaque to light. In metals, due to the presence of free electrons moving under the influence of the electric field of a light wave, rapidly alternating currents arise, accompanied by the release of Joule heat. Therefore, the energy of the light wave quickly decreases, turning into the internal energy of the metal. The higher the conductivity of a metal, the more light it absorbs. In Fig. Figure 1 shows a typical dependence of the light absorption coefficient on frequency in the region of the absorption band. It can be seen that an anomalous dispersion is observed inside the absorption band. However, the absorption of light by a substance must be significant to affect the course of the refractive index.

The dependence of the absorption coefficient on the wavelength (frequency) explains the color of the absorbing bodies. For example, glass that weakly absorbs red and orange rays and strongly absorbs green and blue rays will appear red when illuminated with white light. If green and blue light is directed at such glass, the glass will appear black due to the strong absorption of these wavelengths. This phenomenon is used in the manufacture light filters, which depending on the chemical Glass compositions transmit light only at certain wavelengths, absorbing others.