Where variance applies. Dispersion of light. Decomposition of white light by a prism. Vehicle color and road accidents

Light dispersion

Decomposition of light into a spectrum due to dispersion when passing through a prism (Newton's experiment).

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 velocity of light in a substance on the wavelength (or frequency). Experimentally discovered by Newton around 1672, although theoretically well enough explained much later.

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

One of the clearest 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 a 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 has the maximum speed in the medium and the minimum degree of refraction,
violet has the minimum speed of light in the medium and the maximum degree of refraction.

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 elude observation. Strictly speaking, anomalous dispersion is widespread, for example, it is observed in almost all gases at frequencies near absorption lines, but in iodine vapors 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 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 associated with 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 the order of decreasing wavelength: from red to violet; the normal (diffraction) spectrum is uniform in all regions and is arranged in the order of increasing wavelengths: from violet to red.

By analogy with the dispersion of light, similar phenomena of the dependence of the propagation of waves of any other nature on the wavelength (or frequency) are also called dispersion. For this reason, for example, the term dispersion law, used as the name of the quantitative relationship between frequency and wavenumber, is applied not only to an electromagnetic wave, but to any wave process.

The dispersion explains the fact that a rainbow appears after rain (more precisely, the fact that the rainbow is multi-colored, not white).

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

Cauchy came up with a formula expressing the dependence of the refractive index of a medium on the wavelength:

…,

Dispersion of light in nature and art

Different colors can be observed due to dispersion.

The rainbow, whose colors are due to dispersion, is one of the key images of culture and art.
Due to the dispersion of light, a colored "play of light" can be observed on the facets of diamonds 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 specially enhanced, emphasized.
The decomposition of light into a spectrum (due to dispersion) when refracted in a prism is a fairly common topic in the visual arts. For example, on the cover of Pink Floyd's Dark Side Of The Moon album, light is refracted in a prism and expanded into a spectrum.

Literature

Yashtold-Govorko V.A. Photography and processing. Shooting, formulas, terms, recipes. - Ed. 4th, abbr. - M .: Art, 1977.

Links

Wikimedia Foundation. 2010.

See what "Light dispersion" is in other dictionaries:

The dependence of the refraction of the index n in VA on the frequency n (wavelength l) of light or the dependence of the phase velocity of light waves on their frequency. The investigation of D. s. decomposition into a spectrum of a beam of white light when it passes through a prism (see SPECTRA ... ... Physical encyclopedia

light dispersion- Phenomena caused by the dependence of the speed of propagation of light on the frequency of light vibrations. [A collection of recommended terms. Issue 79. Physical optics. USSR Academy of Sciences. Scientific and Technical Terminology Committee. 1970] Topics ... ... Technical translator's guide

light dispersion- šviesos skaida statusas T sritis radioelektronika atitikmenys: angl. dispersion of light vok. Lichtdispersion, f; Zerteilung des Lichtes, f rus. light dispersion, f pranc. dispersion de la lumière, f ... Radioelektronikos terminų žodynas

light dispersion- šviesos dispersija statusas T sritis fizika atitikmenys: angl. dispersion of light vok. Lichtdispersion, f; Zerlegung des Lichtes, f rus. light dispersion, f pranc. dispersion de la lumière, f ... Fizikos terminų žodynas

The dependence of the refractive index n of a substance on the frequency ν (wavelength λ) of light or the dependence of the phase velocity (see Phase velocity) of light waves on frequency. The investigation of D. s. decomposition into a spectrum of a beam of white light when passing through ... ... Great Soviet Encyclopedia

The dependence of the refractive index n in wa on the frequency of light v. In the region. the frequencies of light, for which ryh in in is transparent, n increases with increasing v normal D. with. In the region. frequencies corresponding to bands of intense absorption of light in vom, n decreases from ... ... Big Encyclopedic Polytechnic Dictionary

The dependence of the absolute refractive index of a substance on the wavelength of light ... Astronomical Dictionary

To improve this article, is it desirable ?: Add illustrations. Find and place in the form of footnotes links to authoritative sources confirming what has been written. Put down a template card that creatures ... Wikipedia

Dependence of the phase velocity of harmonic waves in a medium on the frequency of their oscillations. dispersion of waves is observed for waves of any nature. The presence of wave dispersion leads to distortion of the signal shape (for example, a sound pulse) when propagating in a medium ... Big Encyclopedic Dictionary

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, cyan, blue and violet. Who showed that white is a combination of all colors, what does a rainbow, beautiful sunsets and sunrises, the shine 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, it was not completely clear 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. This color chaos reigned until the time when Isaac Newton conducted an experiment on the transmission of light through a prism (Fig. 1).

Rice. 1. Path of rays in a prism ()

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

Rice. 2. Newton's experiment ()

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

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 environment.

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, red was the weakest refracted, and violet most of all. 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 more and more in the transition from the red end of the spectrum to the violet, we can conclude: the refractive index of glass increases with increasing frequency of light. This is the essence of the dispersion phenomenon.

Let's remember how the refractive index is related to the speed of light:

n ~ ν; V ~ => ν =

n - refractive index

С - speed of light in vacuum

V is the speed of light in the environment

ν - frequency of light

This means that the higher the frequency of light, the less speed the 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 speed 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 at the same speed m / s. Thus, we found out that the reason for the decomposition of white into a spectrum is the phenomenon of dispersion.

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

The phenomenon of dispersion, discovered and investigated by Newton, waited for its explanation for more than 200 years; it was only in the 19th century that the Dutch scientist Laurens proposed the classical theory of dispersion.

The reason for this phenomenon is in the interaction of external electromagnetic radiation, that is, light with the environment: the higher the frequency of this radiation, the stronger the interaction, and therefore, the more the beam will be deflected.

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 as the frequency decreases.

We saw 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, when talking about the wavelength corresponding to a particular color, they mean the wavelength in vacuum or air. The light corresponding to each color is monochromatic. "Mono" is one, "chromos" is a color.

Rice. 3. Arrangement of colors in the spectrum by wavelengths in 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 is a collection of all colors, this color does not correspond to some strictly defined wavelength.

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

It is the dispersion of light, that is, the dependence of the refractive index on the frequency of the wave, that explains the wonderful 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 fog 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 emanates from space along concentric arcs.

The dispersion also explains the remarkable play of color on the edges 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. The color of the body is determined by the ability of the body to reflect or scatter one or another frequency of electromagnetic radiation.

Bibliography

Tikhomirova S.A., Yavorskiy B.M. Physics (basic level) - M .: Mnemosina, 2012.
Gendenshtein L.E., Dick Yu.I. Physics grade 10. - M .: Mnemosina, 2014.
Kikoin I.K., Kikoin A.K. Physics - 9, Moscow, Education, 1990.

Homework

What conclusions did Newton make after the experiment with a prism?
Give a definition of variance.
What determines body color?

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

Rice. 1. Path of rays in a prism ()

Rice. 2. Newton's experiment ()

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 environment.

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

Let's remember how the refractive index is related to the speed of light:

n ~ ν; V ~ => ν =

n - refractive index

С - speed of light in vacuum

V is the speed of light in the environment

ν - frequency of light

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

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

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 as the frequency decreases.

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

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

Rice. 4. The phenomenon of the rainbow ()

The dispersion also explains the remarkable play of color on the edges of precious stones.

Bibliography

Tikhomirova S.A., Yavorskiy B.M. Physics (basic level) - M .: Mnemosina, 2012.
Gendenshtein L.E., Dick Yu.I. Physics grade 10. - M .: Mnemosina, 2014.
Kikoin I.K., Kikoin A.K. Physics - 9, Moscow, Education, 1990.

Homework

What conclusions did Newton make after the experiment with a prism?
Give a definition of variance.
What determines body color?

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

Diffraction and dispersion- such beautiful and similar words that sound like music to the ears of a physicist! As everyone has already guessed, today we are no longer talking about geometric optics, but about the phenomena caused precisely by the wave nature of light.

Light dispersion

So what is the dispersion of light? In we examined the law of refraction of light. Then we did not think, or rather, did not remember that light (electromagnetic wave) has a certain length. Let's remember:

Light- electromagnetic wave. Visible light is wavelengths ranging from 380 to 770 nanometers.

So, old Newton noticed that the refractive index depends on the wavelength. In other words, red light, falling on the surface and refracting, will deflect to a different angle than yellow, green, and so on. This dependence is called variance.

By passing white light through a prism, a spectrum of all the colors of the rainbow can be obtained. This phenomenon is directly attributed to light dispersion. Since the refractive index depends on the wavelength, then it also depends on the frequency. Accordingly, the speed of light for different wavelengths in matter will also be different

Light dispersion- the dependence of the speed of light in matter on frequency.

Where is light dispersion applied? Yes, everywhere! This is not only a beautiful word, but also a beautiful phenomenon. Dispersion of light in everyday life, nature, technology and art. For example, dispersion flaunts on the cover of Pink Floyd's album.

Light diffraction

Before diffraction, you need to say about her "friend" - interference... After all, interference and diffraction of light are phenomena that are observed simultaneously.

Light interference- this is when two coherent light waves, when superimposed, reinforce each other or, on the contrary, weaken.

Waves is coherent, if the difference between their phases is constant in time, and when they are added, a wave of the same frequency is obtained. The resulting wave will be strengthened (interference maximum) or vice versa weakened (interference minimum) - it depends on the phase difference of the oscillations. Highs and lows during interference alternate, forming an interference pattern.

Light diffraction- one more manifestation of wave properties. It would seem that a ray of light should always propagate in a straight line. But no! Meeting an obstacle, the light deviates from the original direction, as if bending around the obstacle. What conditions are necessary for observing the diffraction of light? Actually, this phenomenon is observed on objects of any size, but it is difficult and almost impossible to observe it on large objects. This is best done on obstacles that are comparable in size to the wavelength. In the case of light, these are very small obstacles.

Light diffraction is called the phenomenon of deflection of light from a rectilinear direction when passing near an obstacle.

Diffraction manifests itself not only for light, but also for other waves. For example, for sound. Or for the waves of the sea. A great example of diffraction is how we hear a Pink Floyd song from a passing car as we stand around the corner. If the sound wave propagated directly, it would simply not reach our ears, and we would stand in complete silence. Agree, boring. But diffraction is much more fun.

To observe the phenomenon of diffraction, a special device is used - diffraction grating... A diffraction grating is a system of obstacles that are comparable in size to the wavelength. These are special parallel strokes engraved on the surface of a metal or glass plate. The distance between the edges of adjacent grating slots is called the grating period or its constant.

What happens to light when it passes through a diffraction grating? Falling on the grating and encountering an obstacle, the light wave passes through a system of transparent and opaque regions, as a result of which it breaks up into separate beams of coherent light, which, after diffraction, interfere with each other. Each wavelength is deflected at a certain angle, and light is decomposed into a spectrum. As a result, we observe the diffraction of light on the grating

Diffraction grating formula:

Here d- lattice period, fi- the angle of deflection of light after passing through the grating, k- the order of the diffraction maximum, lambda Is the wavelength.

Today we learned what the diffraction and light dispersion phenomena are. In the course of optics, problems on the topic of interference, dispersion and diffraction of light are very common. Textbook authors are very fond of such tasks. The same cannot be said about those who have to solve them. If you want to easily cope with tasks, understand the topic, and at the same time save time, contact. They will help you cope with any task!

One of the results of the interaction of light with matter is its dispersion.

Light dispersion is called the dependence of the refractive indexn substances from frequencyν (wavelengthsλ) light or the dependence of the phase velocity of light waves on their frequency.

The dispersion of light is represented as a dependence:

The consequence of dispersion is the decomposition of a white light beam into a spectrum when it passes through a prism (Fig. 10.1). The first experimental observations of light dispersion were carried out in 1672 by I. Newton. He explained this phenomenon by the difference in the masses of the corpuscles.

Consider the dispersion of light in a prism. Let a monochromatic beam of light fall on a prism with refractive angle BUT and refractive index n(fig.10.2) at an angle.


Rice. 10.1	Rice. 10.2

After twofold refraction (on the left and right sides of the prism), the beam is refracted from the original direction at an angle φ. Fig. follows that

Suppose the angles BUT and small, then the angles,, will also be small and instead of the sines of these angles, you can use their values. Therefore, and since , then or.

Hence it follows that

(10.1.1)

those. the angle of deflection of the rays by the prism is the greater, the greater the refractive angle of the prism.

From expression (10.1.1) it follows that the angle of deflection of the rays by the prism depends on the refractive index n, but n Is a function of wavelength, therefore rays of different wavelengths after passing through the prism are deflected at different angles... A beam of white light behind a prism is decomposed into a spectrum called dispersive or prismatic as Newton observed. Thus, using a prism, as well as using a diffraction grating, by decomposing light into a spectrum, it is possible to determine its spectral composition.

Consider differences in diffraction and prismatic spectra.

· Diffraction grating decomposes light directly by wavelength, therefore, from the measured angles (along the directions of the corresponding maxima), the wavelength (frequencies) can be calculated. The decomposition of light into a spectrum in a prism occurs according to the values of the refractive index, therefore, to determine the frequency or wavelength of light, it is necessary to know the dependence or.

· Composite colors in diffractive and prismatic spectra are located differently... We know that the sine of an angle in a diffraction grating is proportional to the wavelength . Consequently, red rays, which have a longer wavelength than violet ones, are deflected more strongly by the diffraction grating.... The prism, on the other hand, decomposes the light rays in the spectrum according to the values of the refractive index, which for all transparent substances decreases with an increase in wavelength (i.e., with a decrease in frequency) (Fig. 10.3).

Therefore, the red rays are deflected by the prism weaker, in contrast to the diffraction grating.

The quantity(or )called dispersion of matter, shows how quickly the refractive index changes with wavelength.

Fig. 10.3 it follows that the refractive index for transparent substances increases with increasing wavelength, hence the modulus also increases with decreasing λ. This dispersion is called normal ... Near absorption lines and bands, the course of the dispersion curve will be different, namely n decreases with decreasing λ. Such a course of addiction n of λ is called anomalous variance ... Let us consider these types of dispersion in more detail.