Questions.

1. What does a continuous spectrum look like?

A continuous spectrum is a strip consisting of all the colors of the rainbow, smoothly transitioning into each other.

2. The light of which bodies produces a continuous spectrum? Give examples.

A continuous spectrum is obtained from the light of solid and liquid bodies (the filament of an electric lamp, molten metal, a candle flame) with a temperature of several thousand degrees Celsius. It is also produced by luminous gases and vapors at high pressure.

3. What do line spectra look like?

Line spectra consist of individual lines of specific colors.

4. How can a line emission spectrum of sodium be obtained?

To do this, you can add a piece of table salt (NaCl) to the burner flame and observe the spectrum through a spectroscope.

5. What light sources produce line spectra?

Line spectra are characteristic of luminous gases of low density.

6. What is the mechanism for obtaining line absorption spectra (i.e., what needs to be done to obtain them)?

Line absorption spectra are obtained by passing light from a brighter and hotter source through low-density gases.

7. How to obtain a line absorption spectrum of sodium and what does it look like?

To do this, you need to pass light from an incandescent lamp through a vessel with sodium vapor. As a result, narrow black lines will appear in the continuous spectrum of light from an incandescent lamp, in the place where the yellow lines are located in the sodium emission spectrum.

8. What is the essence of Kirchhoff’s law regarding line emission and absorption spectra?

Kirchoff's law states that atoms of a given element absorb and emit light waves at the same frequencies.

Introduction……………………………………………………………………………….2

Radiation mechanism………………………………………………………………………………..3

Energy distribution in the spectrum……………………………………………………….4

Types of spectra……………………………………………………………………………………….6

Types of spectral analyzes………………………………………………………7

Conclusion………………………………………………………………………………..9

Literature……………………………………………………………………………….11

Introduction

Spectrum is the decomposition of light into its component parts, rays of different colors.

The method of studying the chemical composition of various substances from their line emission or absorption spectra is called spectral analysis. A negligible amount of substance is required for spectral analysis. Its speed and sensitivity have made this method indispensable both in laboratories and in astrophysics. Since each chemical element of the periodic table emits a line emission and absorption spectrum characteristic only for it, this makes it possible to study the chemical composition of the substance. The physicists Kirchhoff and Bunsen first tried to make it in 1859, building spectroscope. Light was passed into it through a narrow slit cut from one edge of the telescope (this pipe with a slit is called a collimator). From the collimator, the rays fell onto a prism covered with a box lined with black paper on the inside. The prism deflected the rays that came from the slit. The result was a spectrum. After this, they covered the window with a curtain and placed a lit burner at the collimator slit. Pieces of various substances were introduced alternately into the candle flame, and they looked through a second telescope at the resulting spectrum. It turned out that the incandescent vapors of each element produced rays of a strictly defined color, and the prism deflected these rays to a strictly defined place, and therefore no color could mask the other. This led to the conclusion that a radically new method of chemical analysis had been found - using the spectrum of a substance. In 1861, based on this discovery, Kirchhoff proved the presence of a number of elements in the chromosphere of the Sun, laying the foundation for astrophysics.

Radiation mechanism

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 atoms. 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, energy must be transferred to it. 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.

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 (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 by electric current in a lamp is converted into light energy. The thermal source of light is a flame. Grains of soot heat up due to the energy released during fuel combustion and emit light.

Electroluminescence. The energy needed by atoms to emit light can also come from non-thermal sources. During a discharge in gases, the electric field imparts greater kinetic energy to the electrons. Fast electrons experience 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.

Cathodoluminescence. The glow of solids caused by the bombardment of electrons is called cathodoluminescence. Thanks to cathodoluminescence, the screens of cathode ray tubes of televisions glow.

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 chemioluminescence.

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), after which 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 at a vessel containing fluoresceite (an organic dye),

passed through a violet light filter, this liquid begins to glow with green-yellow light, i.e. light of 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.

The main types of radiation and the sources that create them are listed. The most common sources of radiation are thermal.

You will need

• - spectroscope;
• - gas-burner;
• - a small ceramic or porcelain spoon;
• - pure table salt;
• - a transparent test tube filled with carbon dioxide;
• - powerful incandescent lamp;
• - powerful “economical” gas light lamp.

Instructions

For a diffraction spectroscope, take a CD, a small cardboard box, or a cardboard thermometer case. Cut a piece of disk to the size of the box. On the top plane of the box, next to its short wall, place the eyepiece at an angle of approximately 135° to the surface. The eyepiece is a piece of a thermometer case. Select the location for the gap experimentally, alternately piercing and sealing holes on another short wall.

Place a powerful incandescent lamp opposite the spectroscope slit. In the spectroscope eyepiece you will see a continuous spectrum. Such a spectral spectrum exists for any heated object. There are no emission or absorption lines. This spectrum is known as .

Place salt in a small ceramic or porcelain spoon. Point the spectroscope slit at a dark, non-luminous area located above the light burner flame. Introduce a spoonful of . At the moment when the flame turns intensely yellow, in the spectroscope it will be possible to observe the emission spectrum of the salt under study (sodium chloride), where the emission line in the yellow region will be especially clearly visible. The same experiment can be carried out with potassium chloride, copper salts, tungsten salts, and so on. This is what emission spectra look like - light lines in certain areas of a dark background.

Point the working slit of the spectroscope at a bright incandescent lamp. Place a transparent test tube filled with carbon dioxide so that it covers the working slit of the spectroscope. Through the eyepiece, a continuous spectrum can be observed, intersected by dark vertical lines. This is the so-called absorption spectrum, in this case of carbon dioxide.

Point the working slit of the spectroscope at the switched on “economical” lamp. Instead of the usual continuous spectrum, you will see a series of vertical lines located in different parts and having mostly different colors. From this we can conclude that the emission spectrum of such a lamp is very different from the spectrum of a conventional incandescent lamp, which is imperceptible to the eye, but affects the photography process.

Video on the topic

note

There are 2 types of spectroscopes. The first uses a transparent dispersive triangular prism. Light from the object under study is fed to it through a narrow slit and observed from the other side using an eyepiece tube. To avoid light interference, the entire structure is covered with a light-proof casing. It may also consist of elements and tubes isolated from light. The use of lenses in such a spectroscope is not necessary. The second type of spectroscope is diffraction. Its main element is a diffraction grating. It is also advisable to send light from the object through the slit. Pieces from CD and DVD discs are now often used as diffraction gratings in homemade designs. Any type of spectroscope will be suitable for the proposed experiments;

Table salt should not contain iodine;

It is better to carry out experiments with an assistant;

It is better to conduct all experiments in a darkened room and always against a black background.

Helpful advice

In order to obtain carbon dioxide in a test tube, place a piece of ordinary school chalk there. Fill it with hydrochloric acid. Collect the resulting gas in a clean test tube. Carbon dioxide is heavier than air, so it will collect at the bottom of an empty test tube, displacing the air in it. To do this, lower the tube from the gas source, that is, from the test tube in which the reaction took place, into an empty test tube.

The physical term "spectrum" comes from the Latin word spectrum, which means "vision", or even "ghost". But an object named with such a gloomy word is directly related to such a beautiful natural phenomenon as a rainbow.

In a broad sense, spectrum is the distribution of values ​​of a particular physical quantity. A special case is the distribution of frequency values ​​of electromagnetic radiation. The light that is perceived by the human eye is also a type of electromagnetic radiation, and it has a spectrum.

Spectrum discovery

The honor of discovering the spectrum of light belongs to I. Newton. When starting this research, the scientist pursued a practical goal: to improve the quality of lenses for telescopes. The problem was that the edges of the image that could be seen in , were painted in all the colors of the rainbow.

I. Newton conducted an experiment: a ray of light penetrated a darkened room through a small hole and fell on a screen. But in its path a triangular glass prism was installed. Instead of a white spot of light, a rainbow stripe appeared on the screen. White sunlight turned out to be complex, composite.

The scientist complicated the experiment. He began making small holes in the screen so that only one colored ray (for example, red) would pass through them, and behind the screen a second and another screen. It turned out that the colored rays into which the first prism decomposed the light were not decomposed into their component parts when passing through the second prism, they were only deflected. Consequently, these light rays are simple, and they were refracted in different ways, which allowed the light to be divided into parts.

So it became clear that different colors do not come from different degrees of “mixing light with darkness,” as was believed before I. Newton, but are components of light itself. This composition was called the spectrum of light.

I. Newton's discovery was important for its time; it contributed a lot to the study of the nature of light. But the true revolution in science associated with the study of the spectrum of light occurred in the middle of the 19th century.

German scientists R.V. Bunsen and G.R. Kirchhoff studied the spectrum of light emitted by fire, to which evaporations of various salts were mixed. The spectrum varied depending on the impurities. This led researchers to believe that the chemical composition of the Sun and other stars can be judged from light spectra. This is how the method of spectral analysis was born.

SPREAD OF LIGHT

Take three postcards and use scissors to cut a hole the size of a penny in the middle of each card. Make a stand for each card from lumps of plasticine and stick them on the table in a line so that the holes are in one straight line.

Shine a flashlight into the hole of the card that is furthest from you, and look through the hole of the nearest card.

What do you see? What about the path that light takes from a flashlight to your eye?

Move the middle card a couple of centimeters to the side so that it now blocks the path of light. What do you see now? What happened to the light? Can you see any traces of light on the card that is pulled back?

Light travels in a straight line. When all three holes are on the same line, the light spreads from the flashlight along this line and hits your eyes;

When the middle card is shifted, an obstacle appears in the path of the light, and the light cannot go around it, since it travels in a straight line. The card prevents it from going the rest of the way to your eye.

OBTAINING SPECTRUM

There is actually more to the color white than meets the eye. It is a mixture of all the colors of the rainbow - red, orange, yellow, green, blue, indigo and violet. These colors make up what is called the visible spectrum. There are several ways to separate white light into its components. Here's one of them.

Fill a bowl with water and place it on a well-lit surface. Place a mirror inside and tilt it so that it rests on one of the sides of the cuvette.

Look at the reflection that the mirror casts on a nearby surface. What do you see? To make the image clearer, place a sheet of white paper in the place where the reflection is cast.

Light travels in waves. Like sea waves, they have crests called maxima and troughs called minima. The distance from one maximum to another is called the wavelength.

A beam of white light contains rays of light with different wavelengths. Each wavelength corresponds to a specific color. V red has the longest wavelengths. Next come orange, then yellow, green, blue and blue. Violet has the shortest wavelengths.

When white light is reflected in a mirror through water, it is broken down into its component colors. They diverge and form a pattern of parallel stripes of color called a spectrum.

And look at the surface of the CD. Where did the rainbow come from here?

SPECTRUM ON THE CEILING

Fill the glass one-third full with water. Place the books in a stack on some smooth surface. The stack should be slightly higher than the length of the flashlight.

Place the glass on top of a stack of books so that part of it extends slightly beyond the edge of the book and hangs in the air, but the glass does not fall.

Place the flashlight under the hanging part of the glass almost vertically, and secure it in this position with a piece of plasticine so that it does not slip. Turn on the flashlight and turn off the lights in the room.

Look at the ceiling. What do you see?
Repeat the experiment, but now fill the glass two-thirds full. How has the rainbow changed?

The beam of a flashlight falls on a glass filled with water at a slight angle. As a result, white light is decomposed into its constituent components. Colors adjacent to each other continue their path along diverging trajectories and, eventually ending up on the ceiling, give such a wonderful spectrum.