"Electromagnetic waves".
Lesson objectives:
Educational:
- to acquaint students with the features of the propagation of electromagnetic waves;
- consider the stages of creating a theory of the electromagnetic field and experimental confirmation of this theory;
Educational: to acquaint students with interesting episodes of the biography of G. Hertz, M. Faraday, Maxwell D.K., Oersted H.K., A.S. Popova;
Developing: promote the development of interest in the subject.
Demonstrations : slides, video.
DURING THE CLASSES
Today we will get acquainted with the features of the propagation of electromagnetic waves, note the stages of the creation of the theory of the electromagnetic field and the experimental confirmation of this theory, dwell on some biographical data.
Repetition.
To accomplish the objectives of the lesson, we need to repeat some questions:
What is a wave, in particular a mechanical wave? (Propagation of vibrations of particles of matter in space)
What quantities characterize the wave? (wavelength, wave velocity, oscillation period and oscillation frequency)
What is the mathematical relationship between wavelength and oscillation period? (the wavelength is equal to the product of the wave velocity and the oscillation period)
Learning new material.
An electromagnetic wave is in many ways similar to a mechanical wave, but there are differences. The main difference is that no medium is needed to propagate this wave. An electromagnetic wave is the result of the propagation of an alternating electric field and alternating magnetic fields in space, i.e. electromagnetic field.
The electromagnetic field is created by accelerated moving charged particles. Its availability is relative. it special kind matter, is a combination of alternating electric and magnetic fields.
Electromagnetic wave - the propagation of an electromagnetic field in space.
Consider the graph of the propagation of an electromagnetic wave.
The diagram of the propagation of an electromagnetic wave is shown in the figure. It is necessary to remember that the vectors of the electric field strength, magnetic induction and wave propagation velocity are mutually perpendicular.
Stages of the creation of the theory of electromagnetic waves and its practical confirmation.
Hans Christian Oersted (1820) Danish physicist, permanent secretary of the Danish Royal Society (since 1815).
Since 1806 - a professor at this university, since 1829 at the same time director of the Copenhagen Polytechnic School. Oersted's works are devoted to electricity, acoustics, molecular physics.
In 1820, he discovered the action of an electric current on a magnetic needle, which led to the emergence of a new field of physics - electromagnetism. The idea of the relationship between various natural phenomena is characteristic of Oersted's scientific work; in particular, he was one of the first to express the idea that light is an electromagnetic phenomenon. In 1822-1823, independently of J. Fourier, he rediscovered the thermoelectric effect and built the first thermoelement. Experimentally studied the compressibility and elasticity of liquids and gases, invented a piezometer (1822). He conducted research on acoustics, in particular, he tried to detect the occurrence of electrical phenomena due to sound. Investigated deviations from the Boyle-Mariotte law.
Oersted was a brilliant lecturer and popularizer, organized the Society for the Dissemination of Natural Science in 1824, created the first physics laboratory in Denmark, contributed to the improvement of the teaching of physics in educational institutions country.
Oersted is an honorary member of many academies of sciences, in particular the St. Petersburg Academy of Sciences (1830).
Michael Faraday (1831)
The brilliant scientist Michael Faraday was self-taught. At school I received only elementary education and then by virtue of life problems worked and simultaneously studied popular science literature in physics and chemistry. Later, Faraday became a laboratory assistant for a well-known chemist at that time, then surpassed his teacher and did a lot of important things for the development of such sciences as physics and chemistry. In 1821, Michael Faraday learned of Oersted's discovery that electric field creates a magnetic field. After pondering this phenomenon, Faraday set out to get an electric field from the magnetic field and as a constant reminder he carried a magnet in his pocket. Ten years later, he put his motto into practice. Turned magnetism into electricity: a magnetic field creates - electricity
The theoretical scientist derived the equations that bear his name. These equations said that alternating magnetic and electric fields create each other. It follows from these equations that an alternating magnetic field creates a vortex electric field, and it creates an alternating magnetic field. In addition, there was a constant in his equations - this is the speed of light in a vacuum. Those. from this theory it followed that an electromagnetic wave propagates in space with the speed of light in a vacuum. This truly brilliant work was appreciated by many scientists of that time, and A. Einstein said that Maxwell's theory was the most fascinating during his studies.
Heinrich Hertz (1887)
Heinrich Hertz was born a sickly child, but became a very quick-witted student. He liked all the subjects he studied. The future scientist loved to write poetry, work for lathe... After graduating from high school, Hertz entered a higher technical school, but did not want to be narrow specialist and entered the University of Berlin to become a scientist. After entering the university, Heinrich Hertz strived to study in the physics laboratory, but for this it was necessary to deal with the solution of competitive problems. And he set about solving the following problem: does an electric current have kinetic energy? This work was calculated for 9 months, but the future scientist solved it in three months. True, a negative result is incorrect from the modern point of view. The measurement accuracy had to be increased thousands of times, which was not possible then.
While still a student, Hertz defended his doctoral dissertation with excellent marks and received the title of doctor. He was 22 years old. The scientist successfully engaged in theoretical research. Studying Maxwell's theory, he showed high experimental skills, created a device, which is called today an antenna, and with the help of transmitting and receiving antennas, he created and received an electromagnetic wave and studied all the properties of these waves. He realized that the speed of propagation of these waves is finite and equal to the speed of propagation of light in a vacuum. After studying the properties of electromagnetic waves, he proved that they are similar to the properties of light. Unfortunately, this robot completely undermined the scientist's health. At first, the eyes refused, then the ears, teeth and nose ached. He died soon after.
Heinrich Hertz completed the enormous work begun by Faraday. Maxwell transformed Faraday's representations into mathematical formulas, and Hertz transformed mathematical images into visible and audible electromagnetic waves. Listening to the radio, watching television, we must remember this person. It is no accident that the unit of vibration frequency is named in honor of Hertz, and it is no coincidence that the first words transmitted by the Russian physicist A.S. Popov wirelessly, were "Heinrich Hertz", encrypted in Morse code.
Popov Alexander Sergeevich (1895)
Popov improved the receiving and transmitting antenna, and at first communication was carried out at a distance of 250 m, then at 600 m. And in 1899, the scientist established radio communication at a distance of 20 km, and in 1901 - at 150 km. In 1900, radio communications helped carry out rescue operations in Gulf of Finland... In 1901, the Italian engineer G. Marconi carried out radio communications across the Atlantic Ocean.
Let's watch a video fragment where some of the properties of an electromagnetic wave are considered. After watching, we will answer your questions.
Why does the light bulb in the receiving antenna change its glow when a metal rod is introduced?
Why doesn't this happen when replacing a metal rod with a glass one?
Anchoring.
Answer the questions:
What is an electromagnetic wave?
Who created the theory of the electromagnetic wave?
Who studied the properties of electromagnetic waves?
Fill out the answer table in your notebook, marking the question number.
How does the wavelength depend on the oscillation frequency?
(Answer: Inversely proportional)
What happens to the wavelength if the oscillation period of the particles doubles?
(Answer: Will increase 2 times)
How will the oscillation frequency of radiation change when the wave passes into a denser medium?
(Answer: Will not change)
What is the cause of the emission of an electromagnetic wave?
(Answer: Charged particles moving with acceleration)
Where are electromagnetic waves used?
(Answer: cellular telephone, microwave oven, television, radio, etc.)
(Answers to questions)
Homework.
It is necessary to prepare reports on various types of electromagnetic radiation, listing their features and talk about their application in human life. The message should be five minutes long.
- Types of electromagnetic waves:
- Sound waves
- Radio waves
- Microwave radiation
- Infrared radiation
- Visible light
- Ultraviolet radiation
- X-ray radiation
- Gamma radiation
Summarizing.
Literature.
- Kasyanov V.A. Physics grade 11. - M .: Bustard, 2007
- A.P. Rymkevich Collection of problems in physics. - M .: Provision, 2004.
- Maron A.E., Maron E.A. Physics grade 11. Didactic materials. - M .: Bustard, 2004.
- Tomilin A.N. The world of electricity. - M .: Bustard, 2004.
- Encyclopedia for children. Physics. - M .: Avanta +, 2002.
- Yu. A. Khramov Physics. Biographical reference, - M., 1983
The purpose of the lesson: to form the concept of the properties of electromagnetic waves and their propagation.
During the classes
Examination homework by individual survey
1. What are the principles of radio communication?
2. What is the name and how does amplitude modulation occur?
3. What is the name and how is the detection carried out?
4. Problem number 1000. Solution. T = 2π QUOTE c = λ / T; T = λ / s; λ2 / c2 = 4π2LC; C = λ2 / 4π2Lc2; C = 0.28 μF.
5. Problem number 1001. Solution. λ = c T; λ1 = with T1; T = 2 π QUOTE; T1 = 2 π QUOTE; λ = c 2π QUOTE
Λ1 = c 2π QUOTE λ / λ1 = QUOTE; λ2 / λ₁2 = LC / LC₁; C₁ = 1.54.
Learning new material
1. Electromagnetic waves can be refracted, reflected, absorbed ...
Let's consider these phenomena. Demonstration special set consisting of a microwave generator, a horn antenna, a receiving antenna, dielectric bodies, a metal plate, a paraffin prism, a lattice of metal rods.
2. Demonstration and explanation of the teacher to the phenomenon of absorption of electromagnetic waves. 
Different dielectric bodies are placed between the horns of the antennas. Notice that the volume of the sound is significantly reduced. Some of the waves were absorbed by dielectrics.
Conclusion: dielectrics absorb electromagnetic waves.
3. Demonstration and explanation of the teacher to the phenomenon of reflection of electromagnetic waves. 
Instead of dielectric bodies, we place a metal plate in the path of the radio wave.
The sound is not heard at all. Due to the reflection, the waves do not reach the receiver.
Let us verify the validity of the law of wave reflection that the angle of incidence α equal to the angle reflection β. The antenna horns are placed at the same angles to metal sheet... The sound will disappear if the sheet is rotated or removed.
Conclusion: metals reflect electromagnetic waves.
4. Demonstration and explanation of the teacher to the phenomenon of refraction of electromagnetic waves.
At the boundary of the dielectric, electromagnetic waves change their direction - they are refracted. The horns are positioned at an angle to each other and directed towards a paraffin prism. The disappearance of sound is observed when the prism is rotated or when it is removed.
Conclusion: electromagnetic waves are refracted when they hit the dielectric boundary.
5. Demonstration of polarization and proof that electromagnetic waves are transverse.
If a grid of parallel metal rods is placed between the generator and receiver, the rods must be either vertically or horizontally positioned. When the vector E ̄ is parallel to the rods, currents appear in them, which the lattice reflects, like a metal plate.
When the vector E ̄ is perpendicular to the rods, the currents in them are not excited and the electromagnetic wave of the other plane passes through the lattice.
In the figure, we see a polarized wave.
Conclusion: experiments prove that the electromagnetic wave is transverse, and also have the property of polarization.
6. Propagation of electromagnetic waves.
The physical properties and shape of the Earth, the state of the atmosphere affect the propagation of waves. 
Radio waves propagate depending on their wavelength.
So short waves are reflected several times from the ionosphere and the Earth's surface.
Long waves seem to "slide" over the surface of the Earth. Ultra-short radio waves penetrate the ionosphere.
Lesson topic: Properties of electromagnetic waves. Propagation and application of electromagnetic waves.
The purpose of the lesson : repeat mechanical waves and their characteristics; the concept of an electromagnetic wave; their properties, distribution and application. Show the role of experiment in the triumph of theory. Expand the horizons of students.
Proceed activation of independent work children in the lesson.
On the desk a poster that indicates the stages of the class: "Remember - Look - Draw conclusions - Share interesting ideas."
Lesson equipment :
On the table is a set of instruments for studying the properties of electromagnetic waves, a loudspeaker, a universal VUP rectifier, a low-frequency amplifier, wires.
Plane-polarized wave model
Table 1 “Classification of radio waves and their area of application”.
Table No. 2 "Propagation of radio waves"
Multimedia equipment for demonstration of the presentation prepared by the students.
Each student has an assignment sheet ( independent work )
Portraits of scientists (D. Maxwell, G. Hertz, A.S. Popov)
In the lesson, we will study the properties of electromagnetic waves using the example of radio waves (from mm to fractions of hundreds of kilometers). The peculiarity of their distribution and use. Hear interesting messages from your classmates about their application. On the table in front of you are leaflets with assignments, which you will fill in during the lesson.
Lesson steps :
Updating basic knowledge(frontal conversation)
What is a Wave?
Wave types in the direction of change physical quantities and by their nature.
Wave characteristics: - wavelength (distance between adjacent humps (troughs)); - vibration frequency; v is the final velocity of propagation.
The connection between them.
What is an electromagnetic wave?
What do mechanical and electromagnetic waves have in common (they transfer energy and have a finite speed).
II. Learning new material .
Developing the theory of the electromagnetic field, D. Maxwell in the 60s of the IXX century theoretically substantiated the possibility of the existence of electromagnetic waves (based on the differential equations he compiled) and even calculated the speed of their propagation. It coincided with the speed of light v = c = 3 * 10 8 m / s. This gave Maxwell reason to conclude that light is one of the types of electromagnetic waves.
Maxwell's conclusions were not recognized by all physicists - Maxwell's contemporaries. An experimental confirmation of the existence of electromagnetic waves was required. Theory without practice is dead!
Such an experiment was carried out in 1888 by the German physicist G. Hertz. Hertz's experiments brilliantly confirmed Maxwell's theory. But the German physicist did not see the prospect of their application. A.S. Popov, a Russian physicist, managed to find them practical use, i.e. gave them a start in life. Wireless communication was carried out using electromagnetic waves.
To obtain an electromagnetic wave, it is necessary to create charge oscillations high frequency... This can be done in an open oscillatory circuit. The intensity of the radiation of the electromagnetic wave is proportional to the 4th power of the frequency. The antenna does not emit low-frequency vibrations (sound).
Experiment: Modern technical devices allow you to get electromagnetic waves and study their properties. It is better to use waves in the centimeter range (= 3cm). Kilometer waves are emitted by a special microwave generator. The generator emits electromagnetic waves using a horn antenna. The electromagnetic wave reaching the receiver is converted into electrical vibrations and amplified by the amplifier and fed to the loudspeaker. Electromagnetic waves are emitted from the horn antenna away from the horn. A receiving antenna in the form of the same horn receives waves that propagate along its axis. ( general form installation is shown in fig. 81)
Demonstrates the properties of electromagnetic waves :
Passage and absorption of waves (cardboard, glass, wood, plastic, etc.);
Reflection from a metal plate;
Change of direction at the boundary of the dielectric (refraction);
Transverse electromagnetic waves, proven by polarization with metal rods;
Interference;
Task A .
Properties of electromagnetic waves:
Reflected from ... (conductors); (fig. 82)
Pass through ... (dielectrics);
Refract at the border ... (dielectric); (fig. 83)
Interfere - ...;
Are ... (transverse);
Classification of electromagnetic waves - (radio waves).
The attention of students is drawn to table No. 1, on which radio waves are distributed by types, lengths, frequencies, and their area of application is indicated. After studying, they perform task "B":
What electromagnetic waves are called radio waves?
What radio waves are used in:
B) television
C) space communications
Table 1. Classification of radio waves.
| , m | , MHz | Application area |
|
| Over long | 10 5 – 10 4 | 3*10 -3 – 3*10 -2 | Radiotelegraph communication, transmission of weather reports and time signals, communication with a submarine. |
| Long waves | 10 4 – 10 3 | 3*10 -2 – 3*10 -1 | Radio broadcasting, radiotelegraph communication and radiotelephone communication, radio broadcasting. |
| Medium waves | 10 3 – 10 2 | 3*10 -1 - 3 | too |
| Short wave HF | 10 2 - 10 | 3 - 30 | Radio broadcasting, radiotelegraph communication, communication with space satellites, radio amateur communication, etc. |
| Ultrashort VHF waves | 10 – 0,001 | 30 – 3*10 5 | Radio broadcasting, television, radio amateur, space, etc. |
Propagation of radio waves.
How the radio wave propagates is not a secondary issue. In practice, the quality of the reception depends on the solution of this issue.
The following factors influence radio wave propagation:
Physical and geometric properties of the Earth's surface;
The presence of the ionosphere, i.e. ionized gas at an altitude of 100 - 300 km;
Ionization of the air is caused by the electromagnetic radiation of the Sun and the streams of charged particles emitted by it. The conductive ionosphere reflects 10m radio waves. But the ability of the ionosphere to reflect and absorb radio waves varies significantly with the time of day and season.
Table number 2 (see page 85 of the textbook) shows the most typical options propagation of radio waves of different ranges near the surface of the Earth. During the passage of radio waves, both interference and diffraction (bending around the convex surface of the Earth) are observed
The use of radio waves.
Brief student messages with demo self-prepared presentation.
Radio as a means of communication
History cellular
Satellite connection
Microwave therapy
Radio telemetry (pp. 258-259, N.M. Liventsev, Physics course for medical universities) - Larisa Pechenkina.
Determine how long local radio stations work: Independent work
Option 1. Station frequencies.
Radio RIM = 101.7 MHz
Mix master = 102.5 MHz
NTV = 99.8 MHz
STB = 105.7 MHz
Radio center = 103.6 MHz
Victoria = 103.1 MHz
Anchoring :
Why is radio reception better in winter and at night than in summer and day?
Why do radios do not work well when a car passes under an overpass or bridge?
Why are telecentre towers built high?
Why are there zones of “silence” when working on short wavelengths?
Why is it impossible to carry out radio communication between submarines located at some depth in the ocean?
OGAOU SPO
"Belgorod Machine-Building Technical School"
Methodical development physics lesson
on this topic
Physics teacher
Azarov Sergey Nikolaevich
Belgorod
Methodical development of a physics lesson on the topic
"Properties of electromagnetic waves, their propagation and application"
Lesson topic : Properties of electromagnetic waves. Propagation and application of electromagnetic waves. The purpose of the lesson : repeat mechanical waves and their characteristics; the concept of an electromagnetic wave; their properties, distribution and application. Show the role of experiment in the triumph of theory. Expand the horizons of students. Lesson equipment :- On the table is a set of instruments for studying the properties of electromagnetic waves, a loudspeaker, a universal VUP rectifier, a low-frequency amplifier, wires. Plane-polarized wave model Table 1 “Classification of radio waves and their area of application”. Poster "Propagation of radio waves". Student reports. Each student has an assignment sheet (independent work)
- Updating basic knowledge (frontal conversation)
II. Learning new material . Developing the theory of the electromagnetic field, D. Maxwell in the 60s of the IXX century theoretically substantiated the possibility of the existence of electromagnetic waves (based on the differential equations he compiled) and even calculated the speed of their propagation. It coincided with the speed of light v = c = 3 * 10 8 m / s. This gave Maxwell reason to conclude that light is one of the types of electromagnetic waves. Maxwell's conclusions were not recognized by all physicists - Maxwell's contemporaries. An experimental confirmation of the existence of electromagnetic waves was required. Theory without practice is dead! Such an experiment was carried out in 1888 by the German physicist Hertz Hertz. Hertz's experiments brilliantly confirmed Maxwell's theory. But the German physicist did not see the prospect of their application. A.S. Popov, a Russian physicist, managed to find practical application for them, i.e. gave them a start in life. Wireless communication was carried out using electromagnetic waves. In order to obtain an electromagnetic wave, it is necessary to create oscillations of a high-frequency charge. This can be done in an open oscillatory circuit. The intensity of the radiation of the electromagnetic wave is proportional to the 4th power of the frequency. The antenna does not emit low-frequency vibrations (sound). Experiment: Modern technical devices make it possible to obtain electromagnetic waves and study their properties. It is better to use waves in the centimeter range (= 3cm). Kilometer waves are emitted by a special microwave generator. The generator emits electromagnetic waves using a horn antenna. The electromagnetic wave reaching the receiver is converted into electrical vibrations and amplified by the amplifier and fed to the loudspeaker. Electromagnetic waves are emitted from the horn antenna away from the horn. A receiving antenna in the form of the same horn receives waves that propagate along its axis (a general view of the installation is shown in Fig. 81). Demonstrates the properties of electromagnetic waves : 1) Passage and absorption of waves (cardboard, glass, wood, plastic, etc.); 2). Reflection from a metal plate; 3) Change of direction at the boundary of the dielectric (refraction); 4) The transverseness of electromagnetic waves is proved by polarization using metal rods; 5). Interference and diffraction of electromagnetic waves. After the demonstration, students write down the properties of electromagnetic waves and make a reference outline (task A). Task A .Properties of electromagnetic waves:
- Reflected from the conductors. Pass through dielectrics. Refract at the boundary of the dielectric. Interfere (using an aluminum plate) Are transverse.
- What electromagnetic waves are called radio waves? What radio waves are used in:
- Physical and geometric properties of the Earth's surface; The presence of the ionosphere, i.e. ionized gas at an altitude of 100 - 300 km;
- Radio as a means of communication. Formation of Belgorod radio. The history of cellular communications. Satellite connection. Microwave therapy. Satellite system GLONAS.
- Why is radio reception better in winter and at night than in summer and day? Why do radios do not work well when a car passes under an overpass or bridge? Why are telecentre towers built high? Why are there zones of “silence” when working on short wavelengths? Why is it impossible to carry out radio communication between submarines located at some depth in the ocean?
Theme. Scale of electromagnetic waves. Properties of electromagnetic waves in different frequency ranges. Electromagnetic waves in nature and technology
Lesson objectives: consider the scale of electromagnetic waves, characterize waves of different frequency ranges; show the role of various types of radiation in human life, the effect of various types of radiation on a person; systematize the material on the topic and deepen the knowledge of students about electromagnetic waves; develop oral speech learners, learners' creative skills, logic, memory; cognitive ability; to form students' interest in the study of physics; educate accuracy, diligence
Lesson type: lesson in the formation of new knowledge
Form of carrying out: lecture with presentation
Equipment: a computer, multimedia projector, presentation "Scale of electromagnetic waves"
During the classes
1. Organizing time
2. Motivation of educational and cognitive activities
The universe is an ocean of electromagnetic radiation. People live in it, for the most part, not noticing the waves penetrating the surrounding space. Warming up by the fireplace or lighting a candle, a person makes the source of these waves work, without thinking about their properties. But knowledge is power: having discovered the nature of electromagnetic radiation, mankind during the XX century has mastered and put at its service its most diverse types.
3. Statement of the topic and objectives of the lesson
Today we will take a journey along the scale of electromagnetic waves, consider the types of electromagnetic radiation in different frequency ranges. Record the topic of the lesson: “Scale of electromagnetic waves. Properties of electromagnetic waves in different frequency ranges. Electromagnetic waves in nature and technology ".
We will study each radiation according to the following generalized plan. Generalized plan for studying radiation:
1. Band name
2. Frequency
3. Wavelength
4. Who was discovered
5. Source
6. Indicator
7. Application
8. Action on humans
As you study the topic, you must complete the following table:
"Scale of electromagnetic radiation"
4. Presentation of new material
The length of electromagnetic waves is very different: from values of the order of 1013 m (low-frequency oscillations) to 10-10 m (g-rays). Light makes up a tiny fraction of the wide spectrum of electromagnetic waves. Nevertheless, it was by studying this small part of the spectrum that other radiations with unusual properties were discovered.
It is customary to emit low frequency radiation, radio emission, infrared rays, visible light, ultraviolet rays, X-rays and g-radiation. The shortest-wavelength g-radiation emits atomic nuclei.
There is no fundamental difference between individual emissions. All of them are electromagnetic waves generated by charged particles. Electromagnetic waves are detected, ultimately, by their action on charged particles. In a vacuum, radiation of any wavelength travels at a speed of 300,000 km / s. The boundaries between the individual regions of the radiation scale are rather arbitrary.
Radiations of different wavelengths differ from each other in the way they are obtained (antenna radiation, thermal radiation, radiation during deceleration of fast electrons, etc.) and in the registration methods.
Everything listed types electromagnetic radiation is also generated by space objects and is successfully investigated using rockets, artificial earth satellites and spacecraft. First of all, this refers to X-ray and g-radiation, which are strongly absorbed by the atmosphere.
As the wavelength decreases, quantitative differences in wavelengths lead to significant qualitative differences.
Radiation of different wavelengths are very different from each other in their absorption by matter. Shortwave radiation (X-rays and especially g-rays) are weakly absorbed. Substances that are opaque to waves in the optical range are transparent to these radiations. The reflectance of electromagnetic waves also depends on the wavelength. But the main difference between longwave and shortwave radiation is that shortwave radiation exhibits particle properties.
Let's consider each radiation.
Low-frequency radiation occurs in the frequency range from 3 · 10-3 to 3. 105 Hz. This radiation corresponds to a wavelength of 1013 - 105 m. Radiation of such relatively low frequencies can be neglected. The source of low frequency radiation is alternating current generators. They are used for melting and hardening metals.
Radio waves occupy the frequency range 3 · 105 - 3 · 1011 Hz. They correspond to a wavelength of 10 5 - 10 -3 m. The source of radio waves, as well as low-frequency radiation is alternating current... The source is also a radio frequency generator, stars, including the Sun, galaxies and metagalaxies. The indicators are a Hertz vibrator, an oscillatory circuit.
The high frequency of radio waves, in comparison with low-frequency radiation, leads to a noticeable emission of radio waves into space. This allows them to be used to transmit information over different distances. Speech, music (broadcasting), telegraph signals (radio communication), images of various objects (radar) are transmitted.
Radio waves are used to study the structure of matter and the properties of the medium in which they propagate. The study of radio emission from space objects is the subject of radio astronomy. In radio meteorology, processes are studied based on the characteristics of the received waves.
Infrared radiation occupies the frequency range 3 * 1011 - 3.85 * 1014 Hz. They correspond to a wavelength of 2 · 10 -3 - 7.6 · 10 -7 m.
Infrared radiation was discovered in 1800 by astronomer William Herschel. Studying the rise in temperature of a thermometer heated by visible light, Herschel found that the thermometer warms up most outside the visible light region (behind the red region). Invisible radiation, given its place in the spectrum, was called infrared. The source of infrared radiation is the radiation of molecules and atoms under thermal and electrical influences. A powerful source of infrared radiation is the Sun, about 50% of its radiation lies in the infrared region. Infrared radiation accounts for a significant proportion (from 70 to 80%) of the radiation energy of incandescent lamps with a tungsten filament. Infrared radiation emits an electric arc and various gas discharge lamps... The radiation of some lasers lies in the infrared region of the spectrum. Indicators of infrared radiation are photo and thermistors, special photo emulsions. Infrared radiation is used to dry wood, food products and various paints and varnishes(infrared heating), for signaling in case of poor visibility, makes it possible to use optical devices that allow you to see in the dark, as well as when remote control... Infrared beams are used to aim projectiles and missiles at a target, to detect a camouflaged enemy. These rays make it possible to determine the difference in temperatures of individual parts of the surface of planets, the structural features of the molecules of matter (spectral analysis). Infrared photography is used in biology in the study of plant diseases, in medicine in the diagnosis of skin and vascular diseases, in forensic science when detecting fakes. When exposed to humans, it causes an increase in the temperature of the human body.
Visible radiation is the only range of electromagnetic waves perceived by the human eye. Light waves occupy a rather narrow range: 380 - 670 nm (n = 3.85 .1014 - 8. 1014 Hz). The source of visible radiation are valence electrons in atoms and molecules, which change their position in space, as well as free charges moving at an accelerated rate. This part of the spectrum gives a person the maximum information about the world around him. According to their physical properties it is similar to other ranges of the spectrum, being only a small part of the spectrum of electromagnetic waves. Radiation, which has different wavelengths (frequencies) in the range of visible radiation, has different physiological effects on the retina of the human eye, causing a psychological sensation of light. Color is not a property of an electromagnetic light wave in itself, but a manifestation of the electrochemical action of the human physiological system: eyes, nerves, brain. There are approximately seven primary colors distinguishable by the human eye in the visible range (in ascending order of radiation frequency): red, orange, yellow, green, cyan, blue, violet. Memorizing the sequence of the primary colors of the spectrum is facilitated by the phrase, each word of which begins with the first letter of the name of the primary color: "Every Hunter Wants to Know Where the Pheasant Sits." Visible radiation can interfere with the chemical reactions in plants (photosynthesis) and in animals and humans. Visible radiation is emitted by individual insects (fireflies) and some deep-sea fish due to chemical reactions in the body. The absorption of carbon dioxide by plants as a result of the process of photosynthesis and the release of oxygen contributes to the maintenance of biological life on Earth. Also, visible radiation is used when illuminating various objects.
Light is the source of life on Earth and at the same time the source of our ideas about the world around us.
Ultraviolet radiation, not visible to the eye, electromagnetic radiation occupying the spectral region between visible and X-ray radiation within the wavelength range 3.8 ∙ 10 -7 - 3 ∙ 10 -9 m. (N = 8 * 1014 - 3 * 1016 Hz). Ultraviolet radiation was discovered in 1801 by the German scientist Johann Ritter. In studying the blackening of silver chloride by visible light, Ritter found that silver blackens even more effectively in the region beyond the violet end of the spectrum, where there is no visible radiation. The invisible radiation that caused this blackening was called ultraviolet radiation.
The source of ultraviolet radiation is the valence electrons of atoms and molecules, also rapidly moving free charges.
The radiation of solids heated to temperatures of - 3000 K contains a noticeable fraction of ultraviolet radiation of the continuous spectrum, the intensity of which increases with increasing temperature. A more powerful source of ultraviolet radiation is any high-temperature plasma. For various applications ultraviolet radiation, mercury, xenon and other gas-discharge lamps are used. Natural sources of ultraviolet radiation are the Sun, stars, nebulae and other space objects. However, only the long-wavelength part of their radiation (l> 290 nm) reaches the earth's surface. To register ultraviolet radiation at
l = 230 nm, ordinary photographic materials are used; in the shorter wavelength region, special low-gelatin photographic layers are sensitive to it. Photoelectric detectors are used that use the ability of ultraviolet radiation to cause ionization and photoelectric effect: photodiodes, ionization chambers, photon counters, photomultipliers.
In small doses ultraviolet radiation has a beneficial, health-improving effect on humans, activating the synthesis of vitamin D in the body, as well as causing sunburn. A large dose of ultraviolet radiation can cause skin burns and cancerous growths (80% curable). In addition, excessive UV radiation weakens the body's immune system, contributing to the development of certain diseases. Ultraviolet radiation also has a bactericidal effect: under the influence of this radiation, pathogenic bacteria die.
Ultraviolet radiation is applied in fluorescent lamps, in forensic science (forged documents are detected from the photographs), in art history (with the help of ultraviolet rays traces of restoration that are not visible to the eye can be found in the paintings). Window glass practically does not transmit ultraviolet radiation; it is absorbed by iron oxide, which is part of the glass. For this reason, even on a hot sunny day, you cannot sunbathe in the room with the window closed.
The human eye cannot see ultraviolet radiation because the cornea and the eye lens absorb ultraviolet light. Some animals see ultraviolet radiation. For example, a pigeon is guided by the sun even in cloudy weather.
X-rays are electromagnetic ionizing radiation occupying the spectral region between gamma and ultraviolet radiation in the range of wavelengths from 10-12 - 10-8 m (frequencies 3 * 1016 - 3-1020 Hz). X-rays were discovered in 1895 by the German physicist W. K. Roentgen. The most common X-ray source is an X-ray tube in which electrons accelerated by an electric zero bombard a metal anode. X-rays can be produced by bombarding a target with high-energy ions. Some radioactive isotopes, synchrotrons - electron storage devices can also serve as sources of X-ray radiation. Natural sources of X-ray radiation are the Sun and other space objects.
X-ray images of objects are obtained on a special X-ray photographic film. X-rays can be recorded using an ionization chamber, scintillation counter, secondary electronic or channel electron multipliers, microchannel plates. Due to its high penetrating power, X-ray radiation is used in X-ray structural analysis (study of the crystal lattice structure), in the study of the structure of molecules, in the detection of defects in samples, in medicine (X-rays, fluorography, cancer treatment), in flaw detection (detection of defects in castings, rails) , in art history (the discovery of ancient painting hidden under a layer of late painting), in astronomy (in the study of X-ray sources), forensic science. A large dose of X-ray radiation leads to burns and changes in the structure of the human blood. Creation of X-ray detectors and their placement on space stations made it possible to detect X-rays from hundreds of stars, as well as shells supernovae and entire galaxies.
Gamma radiation - short-wave electromagnetic radiation occupying the entire frequency range n = 8 ∙ 1014-10 17 Hz, which corresponds to wavelengths l = 3.8 · 10 -7 - 3 ∙ 10-9 m. Gamma radiation was discovered by the French scientist Paul Villard in 1900. By studying the radiation of radium in a strong magnetic field, Willard discovered shortwave electromagnetic radiation, which does not deflect, like light, magnetic field... It was called gamma radiation. Gamma radiation is associated with nuclear processes, the phenomena of radioactive decay that occur with certain substances, both on Earth and in space. Gamma radiation can be recorded using ionization and bubble chambers, as well as using special photographic emulsions. They are used in the study of nuclear processes, in non-destructive testing. Gamma radiation has a negative effect on humans.
So, low-frequency radiation, radio waves, infrared radiation, visible radiation, ultraviolet radiation, X-rays, g-radiation are different kinds electromagnetic radiation.
If you mentally decompose these types in increasing frequency or decreasing wavelength, you get a wide continuous spectrum - the scale of electromagnetic radiation (the teacher shows the scale). TO dangerous species radiation includes: gamma radiation, X-rays and ultraviolet radiation, the rest are safe.
The division of electromagnetic radiation into ranges is conditional. There is no clear border between the regions. The names of the regions have developed historically, they only serve as a convenient means of classifying radiation sources.
All ranges of the electromagnetic emission scale have common properties:
- the physical nature of all radiations is the same
- all radiation propagates in vacuum at the same speed equal to 3 * 108 m / s
- all emissions exhibit common wave properties (reflection, refraction, interference, diffraction, polarization)
5. Summing up the lesson
At the end of the lesson, students finish working on the table.
Output: The entire scale of electromagnetic waves is evidence that all radiation has both quantum and wave properties. In this case, quantum and wave properties do not exclude, but complement each other. The wave properties are brighter at low frequencies and less bright at high frequencies. Conversely, quantum properties are more pronounced at high frequencies and less brightly at small ones. The shorter the wavelength, the brighter the quantum properties appear, and the longer the wavelength, the brighter the wave properties appear. All this serves as a confirmation of the law of dialectics (transition quantitative changes in high quality).
6. Homework:§ 49 (read), synopsis (learn), fill in the table
the last column (the effect of EMR on a person) and
prepare a message on the use of EMP
