home Interpreter Presentation "Optical devices. Spectral devices"

Presentation "Optical devices. Spectral devices"

The law of propagation of light in a homogeneous medium;
Law of reflection of light;
Law of refraction of light;
What are lenses, how to distinguish them by appearance?

“I sing praise before you in delight

Not expensive stones, not gold, but Glass"

(M.V. Lomonosov, "Letter on the benefits of Glass")

The simplest model The microscope consists of two short focus converging lenses.

The object is placed near the front focus lens .

An enlarged inverted image of an object given by a lens is viewed by the eye through eyepiece .

Erythrocytes in an optical microscope.

A microscope is used to obtain large magnifications when observing small objects.

telescopes

Telescope- an optical device is a powerful spotting scope designed to observe very distant objects - celestial bodies.

Telescope- this is an optical system, which, "snatching" a small area from space, visually bringing the objects located in it closer. The telescope captures the rays of the light flux parallel to its optical axis, collects them at one point (focus) and magnifies them with the help of a lens or, more often, a lens system (eyepiece), which simultaneously converts the diverging light rays into parallel again.

The lens telescope has been improved. To improve image quality, astronomers used Newest technologies glassmaking, and also increased the focal length of telescopes, which naturally led to an increase in their physical dimensions (for example, at the end of the 18th century, the length of the telescope of Jan Hevelius reached 46 m).

The eye as an optical apparatus.

Eye - a complex optical system formed from organic materials in the process of long-term biological evolution.

The structure of the human eye

The image is real, reduced and reversed (inverted).

Image position for:

a- normal eye; b- myopic eye;

in- far-sighted eye;

G- correction of myopia;

d- correction of farsightedness

Camera.

Any camera consists of: an opaque camera, a lens (an optical device consisting of a system of lenses), a shutter, a mechanism for focusing and a viewfinder.

Building an image in a camera

When photographing, the subject is located at a distance greater than the focal length of the lens.

The image is real, reduced and reversed (inverted)

What radiation is called white light?
What is a spectrum?
Tell us about the decomposition of radiation into a spectrum using a prism.
By whom and in what year was the first experiment on the decomposition of white light into a spectrum carried out?
Tell us about the diffraction grating. (what it is, what it is intended for)

slide 1

slide 2

Content Types of radiation Light sources Spectra Spectral apparatus Types of spectra Spectral analysis

slide 3

Types of radiation Thermal radiation Electroluminescence Chemiluminescence Photoluminescence Contents

slide 4

Thermal radiation The simplest and most common type of radiation is thermal radiation, in which the energy losses of atoms for the emission of light are compensated by the energy of the thermal motion of the atoms (or molecules) of the radiating body. The higher the body temperature, the faster the atoms move. When fast atoms (or molecules) collide with each other, part of their kinetic energy is converted into excitation energy of atoms, which then emit light. The heat source of radiation is the Sun, as well as an ordinary incandescent lamp. The lamp is a very convenient, but uneconomical source. Only about 12% of all the energy released in the lamp filament by electric current is converted into light energy. Finally, the heat source of light is the flame. Grains of soot (fuel particles that did not have time to burn) are heated by the energy released during the combustion of the fuel and emit light. Types of radiation

slide 5

Electroluminescence The energy needed by atoms to emit light can also be borrowed from non-thermal sources. When discharging in gases, the electric field imparts a large kinetic energy to the electrons. Fast electrons experience inelastic collisions with atoms. Part of the kinetic energy of electrons goes to the excitation of atoms. Excited atoms give off energy in the form of light waves. Due to this, the discharge in the gas is accompanied by a glow. This is electroluminescence. The northern lights are a manifestation of electroluminescence. Streams of charged particles emitted by the Sun are captured magnetic field Earth. They excite the atoms of the upper layers of the atmosphere near the magnetic poles of the Earth, due to which these layers glow. Electroluminescence is used in tubes for advertising signs. Types of radiation

slide 6

Chemiluminescence In some chemical reactions that release energy, part of this energy is directly spent on the emission of light. The light source remains cold (it has a temperature environment). This phenomenon is called chemiluminescence. In the summer in the forest you can see a firefly insect at night. A small green "flashlight" "burns" on his body. You won't burn your fingers by catching a firefly. A luminous spot on its back has almost the same temperature as the surrounding air. Other living organisms also have the property of glowing: bacteria, insects, many fish that live at great depths. Pieces of rotting wood often glow in the dark. Types of radiation Content

Slide 7

Photoluminescence Light incident on a substance is partly reflected and partly absorbed. The energy of the absorbed light in most cases causes only heating of the bodies. However, some bodies themselves begin to glow directly under the action of the radiation incident on it. This is photoluminescence. Light excites the atoms of matter (increases their internal energy), and after that they are highlighted by themselves. For example, luminous paints, which cover many Christmas decorations emit light after being irradiated. The light emitted during photoluminescence has, as a rule, a longer wavelength than the light that excites the glow. This can be observed experimentally. If a light beam passed through a violet light filter is directed to a vessel with fluorescein (organic dye), then this liquid begins to glow with green-yellow light, i.e., light of a longer wavelength than that of violet light. The phenomenon of photoluminescence is widely used in fluorescent lamps. The Soviet physicist S.I. Vavilov proposed covering the inner surface of the discharge tube with substances capable of glowing brightly under the action of short-wave radiation from a gas discharge. Fluorescent lamps are about three to four times more economical than conventional incandescent lamps. Content

Slide 8

Light sources The light source must consume energy. Light is electromagnetic waves with a wavelength of 4×10-7-8×10-7 m. Electromagnetic waves are emitted during the accelerated movement of charged particles. These charged particles are part of the atoms that make up matter. But, without knowing how the atom is arranged, nothing reliable can be said about the mechanism of radiation. It is only clear that there is no light inside an atom, just as there is no sound in a piano string. Like a string that begins to sound only after a hammer strike, atoms give birth to light only after they are excited. In order for an atom to begin to radiate, it needs to transfer a certain amount of energy. By radiating, an atom loses the energy it has received, and for the continuous glow of a substance, an influx of energy to its atoms from the outside is necessary. Content

Slide 9

Spectral Apparatus For an accurate study of spectra, such simple devices as a narrow slit limiting the light beam and a prism are no longer sufficient. Instruments are needed that give a clear spectrum, that is, instruments that separate waves of different wavelengths well and do not allow (or almost do not allow) overlapping of individual sections of the spectrum. Such devices are called spectral devices. Most often, the main part of the spectral apparatus is a prism or diffraction grating. Consider the scheme of the device of the prism spectral apparatus (Fig. 46). The studied radiation first enters the part of the device called the collimator. The collimator is a tube, at one end of which there is a screen with a narrow slit, and at the other end there is a converging lens L1. Content

slide 10

The gap is on focal length from the lens. Therefore, a divergent light beam that enters the lens from the slit exits it as a parallel beam and falls on the prism P. Since different frequencies correspond to different refractive indices, parallel beams that do not coincide in direction come out of the prism. They fall on lens L2. At the focal length of this lens is a screen - frosted glass or photographic plate. Lens L2 focuses parallel beams of rays on the screen, and instead of a single image of the slit, a whole series of images is obtained. Each frequency (more precisely, a narrow spectral interval) has its own image. All these images together form a spectrum. The described instrument is called a spectrograph. If instead of a second lens and a screen, a telescope is used for visual observation of spectra, then the device is called a spectroscope. Prisms and other details of spectral devices are not necessarily made of glass. Instead of glass, transparent materials such as quartz, rock salt, etc. are also used.

slide 11

Spectra According to the nature of the distribution of values of a physical quantity, spectra can be discrete (linear), continuous (continuous), and also represent a combination (superposition) of discrete and continuous spectra. Examples of line spectra are mass spectra and spectra of bound-bound electronic transitions of an atom; examples of continuous spectra are the spectrum of electromagnetic radiation of a heated solid and the spectrum of free electronic transitions of an atom; examples of combined spectra are the emission spectra of stars, where chromospheric absorption lines or most of the sound spectra are superimposed on the continuous spectrum of the photosphere. Another criterion for typifying spectra is the physical processes underlying their production. So, according to the type of interaction of radiation with matter, the spectra are divided into emission (radiation spectra), adsorption (absorption spectra) and scattering spectra. Content

slide 12

slide 13

Continuous Spectra The solar spectrum or the spectrum of an arc lantern is continuous. This means that all wavelengths are represented in the spectrum. There are no discontinuities in the spectrum, and a continuous multicolored band can be seen on the spectrograph screen (Fig. V, 1). Rice. V Emission spectra: 1 - continuous; 2 - sodium; 3 - hydrogen; 4 -helium. Absorption spectra: 5 - solar; 6 - sodium; 7 - hydrogen; 8 - helium. Content

slide 14

The frequency distribution of energy, i.e., the spectral density of radiation intensity, is different for different bodies. For example, a body with a very black surface emits electromagnetic waves of all frequencies, but the dependence of the spectral density of the radiation intensity on frequency has a maximum at a certain frequency nmax. The radiation energy attributable to very small and very high frequencies is negligible. As the temperature rises, the maximum spectral density of the radiation shifts towards short waves. Continuous (or continuous) spectra, as experience shows, give bodies that are in a solid or liquid state, as well as highly compressed gases. To obtain a continuous spectrum, you need to heat the body to high temperature. The nature of the continuous spectrum and the very fact of its existence are determined not only by the properties of individual radiating atoms, but also depend to a large extent on the interaction of atoms with each other. A continuous spectrum is also produced by high-temperature plasma. Electromagnetic waves are emitted by plasma mainly when electrons collide with ions. Types of spectra Contents

slide 15

Line Spectra Let us introduce into the pale flame of a gas burner a piece of asbestos moistened with a solution of common table salt. When observing a flame through a spectroscope, a bright yellow line flashes against the background of a barely distinguishable continuous spectrum of the flame. This yellow line is given by sodium vapor, which is formed during the splitting of sodium chloride molecules in a flame. The figure also shows the spectra of hydrogen and helium. Each of them is a palisade of colored lines of varying brightness, separated by wide dark stripes. Such spectra are called line spectra. The presence of a line spectrum means that the substance emits light only of quite certain wavelengths (more precisely, in certain very narrow spectral intervals). In the figure you see an approximate distribution of the spectral density of the radiation intensity in the line spectrum. Each line has a finite width. Content

slide 16

Line spectra give all substances in the gaseous atomic (but not molecular) state. In this case, light is emitted by atoms that practically do not interact with each other. This is the most fundamental, basic type of spectra. Isolated atoms emit strictly defined wavelengths. Usually, line spectra are observed using the glow of the vapors of a substance in a flame or the glow of a gas discharge in a tube filled with the gas under study. With an increase in the density of an atomic gas, individual spectral lines expand, and, finally, with a very large compression of the gas, when the interaction of atoms becomes significant, these lines overlap each other, forming a continuous spectrum. Types of spectra Contents

slide 17

Striped Spectra A striped spectrum consists of individual bands separated by dark gaps. With the help of a very good spectral apparatus, it can be found that each band is a collection of a large number of very closely spaced lines. In contrast to line spectra, striped spectra are created not by atoms, but by molecules that are not bonded or weakly bonded to each other. To observe molecular spectra, as well as to observe line spectra, one usually uses the glow of vapors in a flame or the glow of a gas discharge. Types of spectra Contents

slide 18

Absorption spectra All substances, the atoms of which are in an excited state, emit light waves, the energy of which is distributed in a certain way over the wavelengths. The absorption of light by a substance also depends on the wavelength. So, red glass transmits the waves corresponding to red light (l» 8 × 10-5 cm), and absorbs all the rest. If white light is passed through a cold, non-radiating gas, then dark lines appear against the background of the continuous spectrum of the source. The gas absorbs most intensely the light of precisely those wavelengths that it emits when it is very hot. The dark lines against the background of the continuous spectrum are the absorption lines, which together form the absorption spectrum. Types of spectra Contents

slide 19

Spectral analysis Line spectra play a particularly important role because their structure is directly related to the structure of the atom. After all, these spectra are created by atoms that do not experience external influences. Therefore, getting acquainted with line spectra, we thereby take the first step towards studying the structure of atoms. By observing these spectra, scientists were able to "look" inside the atom. Here, optics comes into close contact with atomic physics. The main property of line spectra is that the wavelengths (or frequencies) of the line spectrum of a substance depend only on the properties of the atoms of this substance, but are completely independent of the method of excitation of the luminescence of atoms. The atoms of any chemical element give a spectrum that is not like the spectra of all other elements: they are able to emit a strictly defined set of wavelengths. Spectral analysis is based on this - a method for determining the chemical composition of a substance from its spectrum. Like human fingerprints, line spectra have a unique personality. The uniqueness of the patterns on the skin of the finger often helps to find the criminal. In the same way, due to the individuality of the spectra, it is possible to determine the chemical composition of the body. With the help of spectral analysis, it is possible to detect this element in the composition of a complex substance, even if its mass does not exceed 10-10 g. This is a very sensitive method. Presentation Content

slide 2

Classification of spectral instruments.

slide 3

Spectral devices are devices in which light is decomposed into wavelengths and the spectrum is recorded. There are many different spectral instruments that differ from each other in registration methods and analytical capabilities.

slide 4

Having chosen a light source, care must be taken to ensure that the resulting radiation is effectively used for analysis. This is achieved the right choice spectral instrument

slide 5

There are filter and dispersive spectral devices. In filter filters, a narrow range of wavelengths is allocated with a light filter. In dispersive - the radiation of the source is decomposed into wavelengths in a dispersive element - a prism or a diffraction grating. Filter devices are used only for quantitative analysis, dispersion - for qualitative and quantitative

slide 6

There are visual, photographic and photoelectric spectral devices. Steeloscopes - devices with visual registration, Spectrographs - devices with photographic registration. Spectrometers - devices with photoelectric registration. Filter devices - with photoelectric registration. In spectrometers, decomposition into a spectrum is done in a monochromator, or in a polychromator. Instruments based on a monochromator are called single-channel spectrometers. Devices based on a polychromator - multichannel spectrometers.

Slide 7

All dispersive devices are based on the same circuit diagram. Devices may differ in the method of registration and optical characteristics, they may have different appearance and design, but the principle of their operation is always the same Principal diagram of a spectral device. S - entrance slit, L 1 - collimator lens, L 2 - focusing lens, D - dispersing element, R - recording device.

Slide 8

S L 1 D L 2 R The light from the source enters the spectral device through a narrow slit and from each point of this slit in the form of divergent beams enters the collimator lens, which converts the divergent beams into parallel ones. The slit and lens of the collimator constitute the collimator part of the device. Parallel beams from the collimator lens enter the dispersive prism element or a diffraction grating, where they are decomposed into wavelengths. From the dispersing element, light of one wavelength, coming from one point of the slit, exits in a parallel beam and enters the focusing lens, which collects each parallel beam at a certain point on its focal surface - on the recording device. Individual dots form numerous monochromatic images of the slit. If light is emitted by individual atoms, then a series of individual images of the gap in the form of narrow lines is obtained - a line spectrum. The number of lines depends on the complexity of the spectrum of radiating elements and the conditions of their excitation. If individual molecules glow in the source, then lines close in wavelength are collected into bands forming a striped spectrum. The principle of operation of the spectral device.

Slide 9

slot appointment

R S Entrance slit - image object Spectral line - monochromatic image of the slit, built using objectives.

Slide 10

lenses

L 2 L 1 lens spherical mirror

slide 11

collimator lens

S F O L1 The slit is located in the focal surface of the collimator lens. After the collimator lens, from each point of the slit, the light travels in a parallel beam.

slide 12

Focusing lens

Spectral line F O L2 Builds an image of each slit point. It is formed from dots. the slit image is a spectral line.

slide 13

dispersing element

D Dispersive prism diffraction grating

Slide 14

Dispersive prism ABCD - base of the prism, ABEF and FECD - refractive faces, Between refractive faces - refractive angle EF - refractive edge.

slide 15

Types of dispersive prisms

60-degree prism Cornu quartz prism; 30-degree prism with mirror face;

slide 16

rotary prisms

Rotary prisms play a supporting role. They do not decompose the radiation into wavelengths, but only rotate it, making the device more compact. Rotate 900 Rotate 1800

Slide 17

combined prism

The constant deflection prism consists of two 30-degree dispersive prisms and one rotary prism.

Slide 18

The path of a monochromatic beam in a prism

 i In a prism, the light beam is refracted twice on the refracting faces and leaves it, deviating from the original direction by the deflection angle . The angle of deflection depends on the angle of incidence i and the wavelength of the light. At a certain i, the light passes in the prism parallel to the base, the deflection angle is minimal. In this case, the prism operates under conditions of the smallest deflection.

Slide 19

The course of rays in a prism

2 1  1 2 Decomposition of light occurs due to the fact that light of different wavelengths is refracted in a prism in different ways. Each wavelength has its own deflection angle.

Slide 20

Angular dispersion

1 2 Angular dispersion B is a measure of the efficiency of light decomposition into wavelengths in a prism. Angular dispersion shows how much the angle between two nearest beams changes with wavelength:

slide 21

Dependence of the dispersion on the material of the prism quartz glass

slide 22

Dependence of the angular dispersion on the refractive angle

glass glass

These are spectra containing all wavelengths of a certain range. These are spectra containing all wavelengths of a certain range. Radiate heated solid and liquid substances, gases heated under high pressure. They are the same for different substances, so they cannot be used to determine the composition of a substance

Consists of separate lines of different or the same color, having different arrangements Consists of separate lines of different or the same color, having different arrangements Emitted by gases, vapors of low density in the atomic state Allows one to judge the chemical composition of the light source by spectral lines

This is a set of frequencies absorbed by a given substance. The substance absorbs those lines of the spectrum that it emits, being a source of light. This is a set of frequencies absorbed by this substance. The substance absorbs those lines of the spectrum that it emits, being a source of light. Absorption spectra are obtained by passing light from a source that gives a continuous spectrum through a substance whose atoms are in an unexcited state.

Pointing a very large telescope at a short meteor flash in the sky is almost impossible. But on May 12, 2002, astronomers were lucky - a bright meteor accidentally flew just where the narrow slit of the spectrograph at the Paranal observatory was directed. At this time, the spectrograph examined the light. Pointing a very large telescope at a short meteor flash in the sky is almost impossible. But on May 12, 2002, astronomers were lucky - a bright meteor accidentally flew just where the narrow slit of the spectrograph at the Paranal observatory was directed. At this time, the spectrograph examined the light.

The method of determining the qualitative and quantitative composition of a substance by its spectrum is called spectral analysis. Spectral analysis is widely used in mineral exploration to determine the chemical composition of ore samples. It is used to control the composition of alloys in the metallurgical industry. On its basis, the chemical composition of stars, etc., was determined. The method of determining the qualitative and quantitative composition of a substance by its spectrum is called spectral analysis. Spectral analysis is widely used in mineral exploration to determine the chemical composition of ore samples. It is used to control the composition of alloys in the metallurgical industry. On its basis, the chemical composition of stars, etc., was determined.

To obtain the radiation spectrum of the visible range, a device called a spectroscope is used, in which the human eye serves as a radiation detector. To obtain the radiation spectrum of the visible range, a device called a spectroscope is used, in which the human eye serves as a radiation detector.

In the spectroscope, the light from the investigated source 1 is directed to the slot 2 of the tube 3, called the collimator tube. The slit emits a narrow beam of light. At the second end of the collimator tube there is a lens that converts the divergent beam of light into a parallel one. A parallel beam of light coming out of the collimator tube falls on the face of a glass prism 4. Since the refractive index of light in glass depends on the wavelength, then a parallel beam of light, consisting of waves of different lengths, decomposes into parallel beams of light of different colors, traveling along different directions. The telescope lens 5 focuses each of the parallel beams and produces an image of the slit in each color. Multi-colored images of the slit form a multi-colored band - the spectrum. In the spectroscope, the light from the investigated source 1 is directed to the slot 2 of the tube 3, called the collimator tube. The slit emits a narrow beam of light. At the second end of the collimator tube there is a lens that converts the divergent beam of light into a parallel one. A parallel beam of light coming out of the collimator tube falls on the face of a glass prism 4. Since the refractive index of light in glass depends on the wavelength, then a parallel beam of light, consisting of waves of different lengths, decomposes into parallel beams of light of different colors, traveling along different directions. The telescope lens 5 focuses each of the parallel beams and produces an image of the slit in each color. Multi-colored images of the slit form a multi-colored band - the spectrum.

The spectrum can be observed through an eyepiece used as a magnifying glass. If a photograph of the spectrum is to be obtained, then a photographic film or photographic plate is placed in the place where a real image of the spectrum is obtained. A device for photographing spectra is called a spectrograph.

The researcher, using an optical spectroscope, saw different spectra in four observations. Which of the spectra is the spectrum of thermal radiation? The researcher, using an optical spectroscope, saw different spectra in four observations. Which of the spectra is the spectrum of thermal radiation?

Which bodies are characterized by striped absorption and emission spectra? Which bodies are characterized by striped absorption and emission spectra? For heated solids For heated liquids For rarefied molecular gases For heated atomic gases For any of the bodies listed above

Which bodies are characterized by line absorption and emission spectra? Which bodies are characterized by line absorption and emission spectra? For heated solids For heated liquids For rarefied molecular gases For heated atomic gases For any of the bodies listed above

The work can be used for lessons and reports on the subject "Physics"

Our ready-made physics presentations make complex lesson topics simple, interesting and easy to digest. Most of the experiments studied in physics lessons cannot be carried out under normal school conditions; such experiments can be shown using physics presentations. In this section of the site you can download ready-made physics presentations for grades 7,8,9,10,11, as well as presentation-lectures and presentation-seminars in physics for students.