Presentation "Spectra. Spectral analysis. Spectral devices." Presentation on the topic "spectral devices." Spectra and spectral apparatus presentation
- The law of light propagation in a homogeneous medium;
- Law of light reflection;
- Law of light refraction;
- What types of lenses are there, how can you tell them apart by appearance?
“I sing praises before you in delight
Not expensive stones, not gold, but Glass"
(M.V. Lomonosov, “Letter on the benefits of Glass”)
The simplest model of a microscope consists of two short-focus collecting lenses.
The object is placed near the front focus lens .
The enlarged inverted image of an object given by the lens is viewed by the eye through eyepiece .
Red blood cells in an optical microscope.
A microscope is used to obtain high magnifications when observing small objects.
Telescopes
Telescope- the optical device is a powerful telescope designed for observing very distant objects - celestial bodies.
Telescope is an optical system that, “snatching” a small area from space, visually brings objects located in it closer. The telescope captures rays of light parallel to its optical axis, collects them at one point (focus) and magnifies them using a lens or, more often, a system of lenses (eyepiece), which simultaneously converts the diverging rays of light into parallel ones.
The lens telescope was improved. To improve image quality, astronomers used the latest glass melting technologies 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 Jan Hevelius’s telescope reached 46 m).
The eye is like an optical apparatus.
Eye – a complex optical system formed from organic materials in the process of long biological evolution.
Structure of the human eye
The image is real, reduced and inverse (inverted).
- 1 - outer tunica albuginea;
- 2 - choroid;
- 3 - retina;
- 4 - vitreous body;
- 5 - lens;
- 6 - ciliary muscle;
- 7 - cornea;
- 8 - Iris;
- 9 - pupil;
- 10 - aqueous humor (anterior chamber);
- 11 - optic nerve
Image position for:
A- normal eye; b- myopic eye;
V- farsighted eye;
G- correction of myopia;
d- correction of farsightedness
Camera.
Any camera consists of: a light-proof camera, a lens (an optical device consisting of a system of lenses), a shutter, a focusing mechanism and a viewfinder.
Constructing an image in a camera
When photographing, the subject is located at a distance greater than the focal length of the lens.
Real image, reduced and inverse (inverted)
- What kind of radiation is called white light?
- What is spectrum called?
- Tell us about the decomposition of radiation into a spectrum using a prism.
- Who and in what year conducted the first experiment on the decomposition of white light into a spectrum?
- Tell us about the diffraction grating. (what it is, what it is intended for)
These are spectra containing all wavelengths of a certain range. These are spectra containing all wavelengths of a certain range. They emit 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 individual lines of different or the same color, having different locations Consists of individual lines of different or the same color, having different locations Emitted by gases, low-density vapors in the atomic state Allows one to judge the chemical composition of the light source from spectral lines
This is a set of frequencies absorbed by a given substance. A substance absorbs those lines of the spectrum that it emits, being a source of light. This is a set of frequencies absorbed by a given substance. A 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 produces 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 right where the narrow slit of the spectrograph at the Paranal Observatory was aimed. 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 right where the narrow slit of the spectrograph at the Paranal Observatory was aimed. At this time, the spectrograph examined the light.
The method of determining the qualitative and quantitative composition of a substance from 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 from 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 spectrum of visible radiation, a device called a spectroscope is used, in which the human eye serves as a radiation detector. To obtain the spectrum of visible radiation, a device called a spectroscope is used, in which the human eye serves as a radiation detector.
In a spectroscope, light from the source 1 under study is directed to the slit 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 diverging beam of light into a parallel one. A parallel beam of light emerging from the collimator tube falls on the edge of glass prism 4. Since the refractive index of light in glass depends on the wavelength, therefore, 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 stripe - a spectrum. In a spectroscope, light from the source 1 under study is directed to the slit 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 diverging beam of light into a parallel one. A parallel beam of light emerging from the collimator tube falls on the edge of glass prism 4. Since the refractive index of light in glass depends on the wavelength, therefore, 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 stripe - a spectrum.
The spectrum can be observed through an eyepiece used as a magnifying glass. If you need to take a photograph of a spectrum, then photographic film or a photographic plate is placed in the place where the actual 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 spectrum is the thermal radiation spectrum? The researcher, using an optical spectroscope, saw different spectra in four observations. Which spectrum is the thermal radiation spectrum?
What bodies are characterized by striped absorption and emission spectra? What 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 above bodies
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 above bodies
The work can be used for lessons and reports on the subject "Physics"
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Contents Types of radiation Light sources Spectra Spectral apparatus Types of spectra Spectral analysis
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Types of radiation Thermal radiation Electroluminescence Chemiluminescence Photoluminescence Contents
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Thermal radiation The simplest and most common type of radiation is thermal radiation, in which the energy lost by atoms to emit light is compensated by the energy of thermal motion of atoms (or molecules) of the emitting 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 the atoms, which then emit light. The thermal source of radiation is the Sun, as well as an ordinary incandescent lamp. The lamp is a very convenient, but low-cost source. Only about 12% of the total energy released into the lamp filament by electric current is converted into light energy. Finally, the thermal source of light is a flame. Grains of soot (fuel particles that have not had time to burn) become heated due to the energy released during fuel combustion and emit light. Types of radiation
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Electroluminescence The energy required by atoms to emit light can also be obtained from non-thermal sources. During a discharge in gases, the electric field imparts greater kinetic energy to the electrons. Fast electrons experience inelastic collisions with atoms. Part of the kinetic energy of electrons goes to excite atoms. Excited atoms release 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 by the Earth's magnetic field. They excite atoms in the upper layers of the atmosphere at the Earth's magnetic poles, causing these layers to glow. Electroluminescence is used in advertising tubes. Types of radiation
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Chemiluminescence In some chemical reactions that release energy, part of this energy is directly spent on the emission of light. The light source remains cool (it is at ambient temperature). This phenomenon is called chemiluminescence. In the summer in the forest you can see the firefly insect at night. A small green “flashlight” “burns” on his body. You won't burn your fingers catching a firefly. The 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, and many fish that live at great depths. Pieces of rotting wood often glow in the dark. Types of radiation Contents
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Photoluminescence Light incident on a substance is partially reflected and partially absorbed. The energy of absorbed light in most cases only causes heating of bodies. However, some bodies themselves begin to glow directly under the influence of radiation incident on them. This is photoluminescence. Light excites the atoms of a substance (increases their internal energy), and after that they are illuminated themselves. For example, the luminous paints that cover many Christmas tree decorations emit light after being irradiated. The light emitted during photoluminescence, as a rule, has a longer wavelength than the light that excites the glow. This can be observed experimentally. If you direct a light beam passed through a violet filter onto a vessel containing fluorescein (an organic dye), the liquid begins to glow with green-yellow light, i.e., light with a longer wavelength than violet light. The phenomenon of photoluminescence is widely used in fluorescent lamps. 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 approximately three to four times more economical than conventional incandescent lamps. Content
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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 by 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 structured, nothing reliable can be said about the radiation mechanism. 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 being struck by a hammer, 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. When emitting, an atom loses the energy it receives, and for the continuous glow of a substance, an influx of energy to its atoms from the outside is necessary. Content
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Spectral apparatus For accurate study of spectra, such simple devices as a narrow slit limiting the light beam and a prism are no longer sufficient. Devices are needed that provide a clear spectrum, that is, devices that well separate waves of different lengths and do not allow (or almost do not allow) overlap of individual parts of the spectrum. Such devices are called spectral devices. Most often, the main part of the spectral apparatus is a prism or diffraction grating. Let's consider the design diagram of a prism spectral apparatus (Fig. 46). The radiation under study first enters a part of the device called a 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 collecting lens L1. Content
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The slit is at the focal length of the lens. Therefore, a diverging light beam incident on the lens from the slit emerges from 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 emerge from the prism. They fall on lens L2. At the focal length of this lens there 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 device is called a spectrograph. If, instead of a second lens and screen, a telescope is used to visually observe spectra, then the device is called a spectroscope. Prisms and other parts of spectral devices are not necessarily made of glass. Instead of glass, transparent materials such as quartz, rock salt, etc. are also used. Contents
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Spectra According to the nature of the distribution of physical quantity values, spectra can be discrete (line), continuous (solid), and also represent a combination (superposition) of discrete and continuous spectra. Examples of line spectra include mass spectra and spectra of bonded-bonded 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 sound spectra are superimposed on the continuous spectrum of the photosphere. Another criterion for typing spectra is the physical processes underlying their production. Thus, according to the type of interaction of radiation with matter, spectra are divided into emission (emission spectra), adsorption (absorption spectra) and scattering spectra. Content
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Continuous Spectra The solar spectrum or arc lamp spectrum is continuous. This means that the spectrum contains waves of all wavelengths. There are no breaks in the spectrum, and a continuous multi-colored strip 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
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The distribution of energy over frequencies, 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 curve of the dependence of the spectral density of radiation intensity on frequency has a maximum at a certain frequency nmax. The radiation energy at very low and very high frequencies is negligible. With increasing temperature, the maximum spectral density of radiation shifts towards shorter waves. Continuous (or continuous) spectra, as experience shows, are given by bodies in the solid or liquid state, as well as highly compressed gases. To obtain a continuous spectrum, the body must be heated to a high temperature. The nature of the continuous spectrum and the very fact of its existence are determined not only by the properties of individual emitting atoms, but also to a strong extent depend 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
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Line spectra Let's add a piece of asbestos moistened with a solution of ordinary table salt into the pale flame of a gas burner. When observing a flame through a spectroscope, a bright yellow line will flash against the background of the barely visible continuous spectrum of the flame. This yellow line is produced by sodium vapor, which is formed when the molecules of table salt are broken down 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 a substance emits light only at certain wavelengths (more precisely, in certain very narrow spectral intervals). In the figure you see the approximate distribution of the spectral density of radiation intensity in the line spectrum. Each line has a finite width. Content
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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. Typically, to observe line spectra, the glow of vapor of a substance in a flame or the glow of a gas discharge in a tube filled with the gas under study is used. As the density of the atomic gas increases, the individual spectral lines expand, and finally, with very high compression of the gas, when the interaction of atoms becomes significant, these lines overlap each other, forming a continuous spectrum. Types of spectra Contents
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Banded spectra The banded spectrum consists of individual bands separated by dark spaces. With the help of a very good spectral apparatus one can discover that each band is a collection of a large number of very closely spaced lines. Unlike line spectra, striped spectra are created not by atoms, but by molecules that are not bound or weakly bound to each other. To observe molecular spectra, as well as to observe line spectra, the glow of vapor in a flame or the glow of a gas discharge is usually used. Types of spectra Contents
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Absorption spectra All substances whose atoms are in an excited state emit light waves, the energy of which is distributed in a certain way over wavelengths. The absorption of light by a substance also depends on the wavelength. Thus, red glass transmits waves corresponding to red light (l»8×10-5 cm), and absorbs all others. If you pass white light through a cold, non-emitting gas, 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 highly heated. Dark lines against the background of a continuous spectrum are absorption lines that together form an absorption spectrum. Types of spectra Contents
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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, by becoming familiar 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 any 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 the atoms. The atoms of any chemical element produce a spectrum that is unlike the spectra of all other elements: they are capable of emitting a strictly defined set of wavelengths. This is the basis of spectral analysis - a method of 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, thanks to the individuality of the spectra, it is possible to determine the chemical composition of the body. Using 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 Contents
Continuous spectra are produced by bodies in solid and liquid states, as well as highly compressed gases. Line spectra give all substances in the gaseous atomic state. Isolated atoms emit strictly defined wavelengths. Striped spectra, in contrast to line spectra, are created not by atoms, but by molecules that are not bound or weakly bound to each other.
They produce bodies in solid and liquid states, as well as dense gases. To obtain it, you need to heat the body to a high temperature. The nature of the spectrum depends not only on the properties of individual emitting atoms, but also on the interaction of atoms with each other. The spectrum contains waves of all lengths and there are no breaks. A continuous spectrum of colors can be observed on a diffraction grating. A good demonstration of the spectrum is the natural phenomenon of a rainbow. Uchim.net
All substances are produced in a gaseous atomic (but not molecular) state (the atoms practically do not interact with each other). Isolated atoms of a given chemical element emit waves of a strictly defined length. For observation, the glow of vapor of a substance in a flame or the glow of a gas discharge in a tube filled with the gas under study is used. As the density of the atomic gas increases, individual spectral lines broaden. Uchim.net
The spectrum consists of individual bands separated by dark spaces. Each stripe is a collection of a large number of very closely spaced lines. They are created by molecules that are not bound or weakly bound to each other. For observation, the glow of vapors in a flame or the glow of a gas discharge is used. Uchim.net
Gustav Robert Kirchhoff Robert Wilhelm Bunsen Uchim.net Spectral analysis is a method of determining the chemical composition of a substance from its spectrum. Developed in 1859 by German scientists G. R. Kirchhoff and R. W. Bunsen.
If white light is passed through a cold, non-emitting gas, dark lines will appear against the continuous spectrum of the source. Gas absorbs most intensely the light of those wavelengths that it emits in a highly heated state. Dark lines against the background of a continuous spectrum are absorption lines that together form the absorption spectrum. Uchim.net
New elements are discovered: rubidium, cesium, etc.; We learned the chemical composition of the Sun and stars; Determine the chemical composition of ores and minerals; Method for monitoring the composition of a substance in metallurgy, mechanical engineering, and the nuclear industry. The composition of complex mixtures is analyzed by their molecular spectra. Uchim.net
Spectra of stars are their passports with a description of all stellar features. Stars are composed of the same chemical elements that are known on Earth, but in percentage terms they are dominated by light elements: hydrogen and helium. From the spectrum of a star, you can find out its luminosity, distance to the star, temperature, size, chemical composition of its atmosphere, speed of rotation around its axis, features of movement around the common center of gravity. A spectral apparatus mounted on a telescope separates star light by wavelength into a spectrum strip. From the spectrum, you can find out what energy comes from the star at different wavelengths and estimate its temperature very accurately.
Stationary spark optical emission spectrometers “METALSKAN –2500”. Designed for precise analysis of metals and alloys, including non-ferrous, ferrous alloys and cast irons. Laboratory electrolysis installation for metal analysis "ELAM". The installation is intended for carrying out gravimetric electrolytic analysis of copper, lead, cobalt and other metals in alloys and pure metals. Currently, television spectral systems (TSS) are widely used in forensic science. - detection of various types of document forgeries: - detection of filled-in, crossed out or faded (faded) texts, records formed by pressed strokes or made on carbon paper, etc.; - identification of tissue structure; - detection of contaminants on fabrics (soot and mineral oil residues) in case of gunshot injuries and transport accidents; - identification of washed-out, as well as traces of blood located on motley, dark and contaminated objects.
