Reasons for limiting waves by frequent
It would seem that there should be waves of all frequencies ($\nu $) from $\nu =0\ Hz$ to $\nu =\infty \ Hz.$ However, since a light wave has corpuscular properties in addition to wave properties, there are some restrictions . Quantum theory claims that electromagnetic radiation is emitted in the form of quanta (portions of energy). Quantum energy (W) is related to its frequency by the expression:
where $h=6.62\cdot (10)^(-34)J\cdot c$ is Planck's constant, $\hbar =\frac(h)(2\pi )=1.05\cdot (10) ^(-34)J\cdot c$ - Planck's constant with a bar. It follows from expression (1) that infinite frequencies are impossible, since there are no quanta with infinitely high energy. The same expression imposes restrictions on low frequencies, since there is a minimum energy guy value ($W_0$), which implies that the minimum frequency ($(\nu )_0$) is equal to:
Note 1
It must be said that to this day the existence of a lower bound on the energy of photons has not been proven in physics. The minimum frequency of about 8 Hz is observed in standing electromagnetic waves between the ionosphere and the earth's surface.
Electromagnetic wave scale
All currently known electromagnetic waves are divided into:
Picture 1.
Each of the ranges has its own characteristics. With increasing frequency, the manifestation of corpuscular properties of radiation increases. Waves different parts spectra are generated in different ways. Each wave range studies its own branch of physics. These parts of the spectrum differ not in their physical nature, but in the way they are received and received. There are no sharp transitions between these types of waves, the sections can overlap, the boundaries are conditional.
The visible part of the spectrum of electromagnetic waves, together with the zone of ultraviolet and infrared radiation, is studied in optics (the so-called optical range). Visible radiation quanta are called photons. Their energy is contained in the interval:
The entire spectrum of electromagnetic radiation has wave and quantum properties, but depending on the wavelength, one type of properties prevails in importance over the other, and, accordingly, different methods are used to study them. Depending on the wavelength different groups waves have various practical applications.
Features of different types of electromagnetic radiation
Features of the optical range are:
- fulfillment of the laws of geometric optics,
- weak interaction of light with matter.
Note 2
For frequencies lower than the optical range, the laws of geometric optics cease to apply, while the electromagnetic field of high frequencies either passes through the substance or destroys it. Visible light is necessary condition life on Earth, as it is a prerequisite for photosynthesis.
radio waves are used for radio communication, television, radar. These are the longest wavelengths in the electromagnetic spectrum. Radio waves are easy to artificially generate using an oscillatory circuit (capacitance and inductance connection). Atoms and molecules are capable of emitting radio waves, which is used in radio astronomy. In the very general view, it should be noted that the emitter of electromagnetic waves are rapidly moving charged particles located in atoms and nuclei.
Infrared spectrum first experimentally studied in 1800 by V. Herschel. The scientist placed the thermometer beyond the red edge of the spectrum and recorded an increase in temperature, which meant that the thermometer was heated by radiation invisible to the eye. Infrared radiation is emitted by any heated body. Using special means, infrared radiation can be converted into visible light. This is how images of heated bodies are obtained in the dark. Infrared radiation is used to dry something.
Ultraviolet radiation was discovered by I. Ritter. He discovered that beyond the violet end of the spectrum there are rays invisible to the eye that affect some chemical compounds. It is able to kill pathogenic bacteria, because of this it is widely used in medicine. Ultraviolet radiation in the composition of the sun's rays affects the human skin, causing it to darken (tan).
X-rays were discovered by W. Roentgen in 1895. They are invisible to the eye, pass without significant absorption through large layers of matter that are opaque to visible light. X-rays are detected by their ability to cause some crystals to glow and to affect photographic film. These beams are used in particular in medical diagnostics. X-ray radiation has a strong biological effect.
Definition 1
Gamma radiation- this is the radiation emitted by excited atomic nuclei and interacting elementary particles. This is the shortest wavelength. It has the most pronounced corpuscular properties. Usually gamma radiation is considered as a stream of gamma - quanta. In the region of wavelengths of the order of $(10)^(-10)-(10)^(-14)m$, the gamma radiation and X-ray ranges overlap.
Example 1
Exercise: What is the emitter for different types of electromagnetic waves?
Solution:
The emitter of electromagnetic waves are always moving charged particles. In atoms and nuclei, these particles move at an accelerated rate, which means that they are sources of electromagnetic waves. Radio waves emit atoms and molecules. This is the only type of wave that can be artificially generated using an oscillatory circuit. Infrared radiation is obtained mainly due to the vibrations of atoms in molecules. These oscillations are called thermal, as they are generated by thermal collisions of molecules. As the temperature increases, the oscillation frequency increases.
Visible beams are generated by individual excited atoms.
Ultraviolet light is also referred to as atomic.
X-rays are emitted due to the fact that electrons with high kinetic energy interact with atoms and nuclei of atoms, or the nuclei of atoms themselves emit due to their own excitation.
Gamma rays are generated by excited nuclei of atoms and arise during the interaction and mutual transformations of elementary particles.
Example 2
Exercise: What are the frequencies of visible waves?
Solution:
Visible range - a set of waves that the human eye perceives. The boundaries of this range depend on individual features human vision, and is approximately within $\lambda =0.38-0.76\ µm.$
In optics, two types of frequencies are used. Circular frequency ($\omega $), which is defined as:
\[\omega =\frac(2\pi )(T)\left(2.1\right),\]
where $T$ is the period of wave oscillations. The frequency $\nu$ is also used, which is related to the oscillation period as:
\[\nu=\frac(1)(T)\left(2.2\right).\]
Therefore, both frequencies are related by the relation:
\[\omega =2\pi \nu \left(2.3\right).\]
Knowing that the propagation velocity of electromagnetic waves in vacuum is equal to $c=3\cdot (10)^8\frac(m)(c)$, we have:
\[\lambda =cT\to T=\frac(\lambda )(c)\left(2.4\right).\]
In this case, for the boundaries of the visible range, we get:
\[\nu =\frac(c)(\lambda ),\ \omega =2\pi \frac(c)(\lambda ).\]
Using the fact that we know the wavelengths for visible light, we get:
\[(\nu )_1=\frac(3\cdot (10)^8)(0.38\cdot (10)^(-6))=7.9\cdot (10)^(14)\left (Hz\right),\ (\nu )_2=\frac(3\cdot (10)^8)(0.76\cdot (10)^(-6))=3.9\cdot (10)^ (14)\left(Hz\right).\] \[(\omega )_1=2\cdot 3,14\cdot 7,9\cdot (10)^(14)=5\cdot (10)^( 15)\left(с^(-1)\right),(\omega )_1=2\cdot 3,14\cdot 3,9\cdot (10)^(14)=2,4\cdot (10) ^(15)\left(c^(-1)\right).\ \]
Answer: $3.9\cdot (10)^(14)Hz
Electromagnetic waves are classified according to the wavelength λ or the wave frequency associated with it f. Note also that these parameters characterize not only the wave but also the quantum properties electro magnetic field. Accordingly, in the first case, the electromagnetic wave is described by the classical laws studied in this course.
Consider the concept of the spectrum of electromagnetic waves. The spectrum of electromagnetic waves called the frequency band of electromagnetic waves that exist in nature.
The spectrum of electromagnetic radiation in order of increasing frequency is:
Different sections of the electromagnetic spectrum differ in the way they emit and receive waves belonging to one or another section of the spectrum. For this reason, there are no sharp boundaries between different parts of the electromagnetic spectrum, but each range is determined by its own characteristics and the prevalence of its laws, determined by the ratios of linear scales.
Radio waves are studied by classical electrodynamics. Infrared light and ultraviolet radiation are studied both by classical optics and quantum physics. X-ray and gamma radiation is studied in quantum and nuclear physics.
Let us consider the spectrum of electromagnetic waves in more detail.
low frequency waves
Low-frequency waves are electromagnetic waves whose oscillation frequency does not exceed 100 kHz). It is this frequency range that is traditionally used in electrical engineering. In the industrial electric power industry, a frequency of 50 Hz is used, at which the transmission of electrical energy is carried out along the lines and the voltage is converted by transformer devices. In aviation and land transport, a frequency of 400 Hz is often used, which gives an advantage in the weight of electrical machines and transformers by 8 times compared to 50 Hz. Switching power supplies of the latest generations use transformation frequencies alternating current units and tens of kHz, which makes them compact, energy-rich.
The fundamental difference between the low-frequency range and higher frequencies is the drop in the speed of electromagnetic waves in proportion to the square root of their frequency from 300 thousand km / s at 100 kHz to about 7 thousand km / s at 50 Hz.
radio waves
Radio waves are electromagnetic waves with wavelengths greater than 1 mm (frequency less than 3 10 11 Hz = 300 GHz) and less than 3 km (above 100 kHz).
Radio waves are divided into:
1. Long waves in the length range from 3 km to 300 m (frequency in the range of 10 5 Hz - 10 6 Hz = 1 MHz);
2. Medium waves in the length range from 300 m to 100 m (frequency in the range 10 6 Hz -3 * 10 6 Hz = 3 MHz);
3. Short waves in the wavelength range from 100m to 10m (frequency in the range 310 6 Hz-310 7 Hz=30 MHz);
4. Ultrashort waves with a wavelength of less than 10m (frequency greater than 310 7 Hz = 30 MHz).
Ultrashort waves, in turn, are divided into:
A) meter waves;
B) centimeter waves;
B) millimeter waves;
Waves with a wavelength less than 1 m (frequency less than 300 MHz) are called microwaves or microwaves.
Due to the large values of the wavelengths of the radio range compared to the size of atoms, the propagation of radio waves can be considered without taking into account the atomistic structure of the medium, i.e. phenomenologically, as is customary in the construction of Maxwell's theory. The quantum properties of radio waves are manifested only for the shortest waves adjacent to the infrared part of the spectrum and during the propagation of the so-called. ultrashort pulses with a duration of the order of 10 -12 sec - 10 -15 sec, comparable with the time of oscillations of electrons inside atoms and molecules.
The fundamental difference between radio waves and higher frequencies is a different thermodynamic relationship between the wavelength of the wave carrier (ether), equal to 1 mm (2.7 °K), and the electromagnetic wave propagating in this medium.
Biological effect of radio wave radiation
The terrible sacrificial experience of using powerful radio wave radiation in radar technology showed the specific effect of radio waves depending on the wavelength (frequency).
The destructive effect on the human body is not so much the average as the peak radiation power, at which irreversible phenomena occur in protein structures. For example, the power of continuous radiation of the magnetron of a microwave oven (microwave oven), which is 1 kW, affects only food in a small closed (shielded) volume of the oven, and is almost safe for a person nearby. The power of a radar station (radar, radar) of 1 kW of average power emitted by short pulses with a duty cycle of 1000: 1 (the ratio of the repetition period to the pulse duration) and, accordingly, a pulse power of 1 MW, is very dangerous for human health and life at a distance of up to hundreds of meters from the emitter. In the latter, of course, the direction of the radar radiation also plays a role, which emphasizes the destructive effect of precisely pulsed, and not average, power.
Impact of meter waves
High-intensity meter waves emitted by pulse generators of meter-long radar stations (RLS) with a pulse power of more than a megawatt (such as, for example, the P-16 early warning station) and commensurate with the length spinal cord of humans and animals, as well as the length of axons, disrupt the conductivity of these structures, causing diencephalic syndrome (UHF disease). The latter leads to the rapid development (over a period of several months to several years) of complete or partial (depending on the received pulsed dose of radiation) irreversible paralysis of the human limbs, as well as a violation of the innervation of the intestines and other internal organs.
Impact of decimeter waves
Decimeter waves are commensurate in wavelength with blood vessels covering such human and animal organs as lungs, liver and kidneys. This is one of the reasons why they cause the development of "benign" tumors (cysts) in these organs. Developing on the surface of blood vessels, these tumors lead to a cessation of normal blood circulation and disruption of the organs. If such tumors are not removed in time by surgery, then the death of the organism occurs. Decimeter waves of dangerous intensity levels are emitted by the magnetrons of such radars as the P-15 mobile air defense radar, as well as the radars of some aircraft.
Impact of centimeter waves
Powerful centimeter waves cause diseases such as leukemia - "leukemia", as well as other forms of malignant tumors in humans and animals. Waves of sufficient intensity for the occurrence of these diseases are generated by P-35, P-37 centimeter-range radars and almost all aircraft radars.
Infrared, light and ultraviolet radiation
infrared, light, ultraviolet radiation are optical region of the spectrum of electromagnetic waves in the broadest sense of the word. This spectrum occupies a range of electromagnetic wave lengths in the range from 2·10 -6 m = 2 μm to 10 -8 m = 10 nm (in frequency from 1.5·10 14 Hz to 3·10 16 Hz). The upper limit of the optical range is determined by the long-wave limit of the infrared range, and the lower limit by the short-wave limit of the ultraviolet (Fig. 2.14).
The closeness of the sections of the spectrum of these waves led to the similarity of the methods and instruments used for their study and practical application. Historically, lenses have been used for this purpose, diffraction gratings, prisms, diaphragms, optically active substances that are part of various optical devices (interferometers, polarizers, modulators, etc.).
On the other hand, the radiation of the optical region of the spectrum has general patterns the passage of various media, which can be obtained using geometric optics, which is widely used for calculations and construction of both optical devices and channels for the propagation of optical signals. infrared radiation is visible to many arthropods (insects, spiders, etc.) and reptiles (snakes, lizards, etc.) , available for semiconductor sensors (infrared photomatrices), but it is not passed by the thickness of the Earth's atmosphere, which does not allow to observe infrared stars from the surface of the Earth - "brown dwarfs", which make up more than 90% of all stars in the Galaxy.
The width of the optical range in frequency is approximately 18 octaves, of which the optical range accounts for approximately one octave (); on ultraviolet - 5 octaves ( 
), for infrared radiation - 11 octaves (
In the optical part of the spectrum, phenomena due to the atomistic structure of matter become significant. For this reason, along with the wave properties of optical radiation, quantum properties appear.
Light
|
Light, light, visible radiation - the part of the optical spectrum of electromagnetic radiation visible to the eyes of humans and primates, occupies a range of electromagnetic wave lengths in the range from 400 nanometers to 780 nanometers, that is, less than one octave - a twofold change in frequency.
Rice. 1.14. Electromagnetic wave scale Verbal meme-memory of the order of colors in the light spectrum: |
X-ray and gamma radiation
In the field of X-ray and gamma radiation, the quantum properties of radiation come to the fore.
x-ray radiation arises during the deceleration of fast charged particles (electrons, protons, etc.), as well as as a result of processes occurring inside the electron shells of atoms.
Gamma radiation is a consequence of phenomena occurring inside atomic nuclei, as well as as a result of nuclear reactions. The boundary between X-ray and gamma radiation is determined conditionally by the magnitude of the energy quantum corresponding to a given radiation frequency.
X-ray radiation consists of electromagnetic waves with a length of 50 nm to 10 -3 nm, which corresponds to a quantum energy of 20 eV to 1 MeV.
Gamma radiation is electromagnetic waves with a wavelength less than 10 -2 nm, which corresponds to a photon energy greater than 0.1 MeV.
The electromagnetic nature of light
Light is the visible part of the spectrum of electromagnetic waves, the wavelengths of which occupy the interval from 0.4 µm to 0.76 µm. Each spectral component of optical radiation can be associated with a specific color. The color of the spectral components of optical radiation is determined by their wavelength. The color of the radiation changes as its wavelength decreases as follows: red, orange, yellow, green, cyan, indigo, violet.
The red light corresponding to the longest wavelength defines the red end of the spectrum. Violet light - corresponds to the purple border.
Natural (daylight, sunlight) light is uncolored and is a superposition of electromagnetic waves from everything visible to man spectrum. Natural light comes from the emission of electromagnetic waves by excited atoms. The nature of excitation can be different: thermal, chemical, electromagnetic, etc. As a result of excitation, atoms emit electromagnetic waves in a chaotic manner for about 10 -8 seconds. Since the energy spectrum of excitation of atoms is quite wide, electromagnetic waves are emitted from the entire visible spectrum, the initial phase, direction and polarization of which is random. For this reason, natural light is not polarized. This means that the "density" of the spectral components of electromagnetic waves of natural light having mutually perpendicular polarizations is the same.
Harmonic electromagnetic waves in the light range are called monochromatic. For a monochromatic light wave, one of the main characteristics is the intensity. light wave intensity is the average value of the energy flux density (1.25) carried by the wave:
Where is the Poynting vector.
Calculation of the intensity of a light, plane, monochromatic wave with amplitude electric field in a homogeneous medium with dielectric and magnetic permeability according to formula (1.35), taking into account (1.30) and (1.32), gives:
Traditionally, optical phenomena are considered with the help of rays. Description optical phenomena with the help of rays is called geometric-optical. The rules for finding ray trajectories developed in geometric optics are widely used in practice for the analysis of optical phenomena and in the construction of various optical devices.
Let's give a definition of a beam based on the electromagnetic representation of light waves. First of all, rays are lines along which electromagnetic waves propagate. For this reason, a ray is a line, at each point of which the average Poynting vector of an electromagnetic wave is directed tangentially to this line.
In homogeneous isotropic media, the direction of the mean Poynting vector coincides with the normal to the wave surface (equiphase surface), i.e. along the wave vector .
Thus, in homogeneous isotropic media, the rays are perpendicular to the corresponding wavefront of an electromagnetic wave.
For example, consider the rays emitted by a point monochromatic light source. From the point of view of geometric optics, a set of rays emanate from the source point in the radial direction. From the position of the electromagnetic essence of light, a spherical electromagnetic wave propagates from the source point. Enough long distance from the source, the curvature of the wave front can be neglected, assuming a locally spherical wave to be plane. By dividing the surface of the wave front into a large number of locally flat sections, it is possible to draw a normal through the center of each section, along which the plane wave propagates, i.e. in the geometric-optical interpretation of the beam. Thus, both approaches give the same description of the considered example.
The main task of geometric optics is to find the direction of the beam (trajectory). The trajectory equation is found after solving the variational problem of finding the minimum of the so-called. actions on the desired trajectories. Without going into details of the rigorous formulation and solution of this problem, we can assume that the rays are trajectories with the smallest total optical length. This statement is a consequence of Fermat's principle.
The variational approach to determining the trajectory of rays can also be applied to inhomogeneous media, i.e. such media, in which the refractive index is a function of the coordinates of the points of the medium. If the function describes the shape of the surface of a wave front in an inhomogeneous medium, then it can be found based on the solution of a partial differential equation, known as the eikonal equation, and in analytical mechanics as the Hamilton-Jacobi equation:
Thus, the mathematical basis of the geometric-optical approximation of the electromagnetic theory is made up of various methods for determining the fields of electromagnetic waves on rays, based on the eikonal equation or in some other way. The geometric-optical approximation is widely used in practice in radio electronics to calculate the so-called. quasi-optical systems.
In conclusion, we note that the ability to describe light simultaneously and from wave positions by solving Maxwell's equations and with the help of rays, the direction of which is determined from the Hamilton-Jacobi equations describing the motion of particles, is one of the manifestations of the apparent dualism of light, which, as is known, led to the formulation logically contradictory principles of quantum mechanics.
In fact, there is no dualism in the nature of electromagnetic waves. As shown by Max Planck in 1900 in his classic work On the Normal Spectrum of Radiation, electromagnetic waves are individual quantized oscillations with a frequency v and energy E=hv, Where h=const, on the air. The latter is a superfluid medium having the stable property of discontinuity with the measure h is Planck's constant. When exposed to the ether with an energy exceeding hv during radiation, a quantized "vortex" is formed. Exactly the same phenomenon is observed in all superfluid media and the formation of phonons in them - quanta of sound radiation.
For the "copy-and-paste" combination of the discovery of Max Planck in 1900 with the photoelectric effect discovered back in 1887 by Heinrich Hertz, in 1921 the Nobel Committee awarded the Nobel Prize
Physics lesson in grade 11
"Traveling the Scale of Electromagnetic Waves"
using design technology and ICT”
Physics teacher, MOU "Gatchinskaya secondary school No. 9 with in-depth study items"
Titova Tatyana Viktorovna
This lesson is held in the 11th grade and is the final in the sections "Electromagnetic waves", "Optics". The duration of the lesson is 2 hours. Students already know the basic properties of electromagnetic waves, the causes of their occurrence, methods for their production and registration, the main characteristics of electromagnetic radiation, they know the formulas that describe wave processes, they can give examples of the practical application of electromagnetic radiation.
Lesson Objectives:
Show the importance of the topic “Spectrum of electromagnetic waves” in the formation of students' ideas about the physical picture of the world; clarify the understanding of the structure of matter;
Show the capabilities of the computer in the organization of the educational process.
Lesson objectives:
generalize, systematize previously studied material on the entire range of electromagnetic radiation;
deepen knowledge on the topic;
to improve the intellectual abilities and speech development of students, to form the ability to highlight the main thing, compare, generalize, draw conclusions;
stimulate interest in the subject by attracting additional material;
create a need to deepen and expand knowledge.
develop curiosity.
Educational:
Developing:
Educational:
lesson type - repetition and consolidation of previously acquired knowledge, control of knowledge and skills of students.
General lesson plan:
Electromagnetic waves;
The history of the discovery of electromagnetic waves;
Properties of electromagnetic waves;
Characteristics and basic properties of electromagnetic waves (general overview of the scale of electromagnetic waves).
Motivation.
Lesson plan message:
Conclusion. Conclusions.
Repetition of formulas on the topic "Quantum Theory";
Summing up the lesson.
Lesson plan
Lesson stage
Teacher activity
Student activities
organizational
Greetings. Communication of goals, objectives, lesson plan
Accept goals cognitive activity preparation for the lesson
Organization of perception of information. Checking previously studied material
Frontal survey, slide show
They answer from the spot, work in a notebook
Repetition of material
View slides, comments on student presentations
Making a table in a notebook
Fixing the topic. Test.
Slideshow, face-to-face
Solving problems at the blackboard, repeating formulas
Summing up the lesson. Independent work. Homework Suggestions
Performance test items, comments of the teacher at registration of work.
Completing a task.
Answers to questions of reflection. Recording homework.
Organizing time. The message of the topic and purpose of the lesson (slide No. 1,2)
Motivation.
Teacher.
In 1862, Maxwell*, based on his theory of electromagnetism, predicted the existence of electromagnetic waves. From his calculations it followed that the speed of their propagation is equal to the previously measured speed of light in air. This fact clearly testified to the electromagnetic nature of light.
The full electromagnetic spectrum occupies an infinitely large range of wavelengths. It starts from the longest: with a wavelength of 1.5 10 13 cm and ends with the shortest gamma rays of radium with a wavelength of 4.7 10 -11 cm.
The longest waves are 3 10 23 times longer than the shortest ones (slide No. 3).
In our Everyday life we are dealing with different types electromagnetic radiation, which are used in science, medicine, i.e. The role of electromagnetic radiation is great, and there is a lot of information about electromagnetic waves.
* Draw students' attention to the portrait of a scientist on the stand.
Lesson plan message (slide #4)
Frontal survey (updating knowledge).
Teacher:
What is an electromagnetic wave? (slide №5,6)
What is the history of electromagnetic waves? (slide №7,8)
List General characteristics and properties that allow you to combine all types of electromagnetic radiation into a scale of electromagnetic waves (slide No. 9).
Students.
The speed of an electromagnetic wave is finite and in vacuum it is equal to the speed of light.
Any accelerating or oscillating charge radiates electromagnetic waves.
Around the source of electromagnetic waves, there is a periodic change in the characteristics of the electric and magnetic fields (vectors of intensity and magnetic induction).
The directions of oscillations of the vectors of magnetic induction are mutually perpendicular, and also perpendicular to the direction of wave propagation, which means that electromagnetic waves are transverse.
Electromagnetic waves have properties: interference, diffraction, polarization.
Overview of the scale of electromagnetic radiation (slide number 10)
Teacher:
Different ranges of electromagnetic waves have received different names, but one should not forget about the general properties of such waves: all types of radiation are of the same nature and differ from each other only in their frequencies. If these frequencies are plotted on a certain scale on the axis, then we get a diagram or a scale of waves*.
Traveling on the scale of electromagnetic waves, you will keep records in a special diary - a table (slide No. 11). (Appendix No. 1).
APPENDIX №1.
TABLE.
Scale of electromagnetic waves.
Spectrum name
Wavelength
Sources
Properties
Application
* Draw students' attention to the scale of electromagnetic waves on the stand.
Students present prepared presentations and mini performances on wave bands.
(low frequency vibrations)
Lead #1.
Electromagnetic waves propagate over great distances, so they transmit information, including sound and images.
Presentation by students (slides #12-19)*
* After each slide, give each student 1 minute. to write to the table.
Solving the problem of applying the ratio of wave motion (slide No. 20)
In 1897, the Russian physicist P.N. Lebedev received electromagnetic radiation with a wavelength of 6 mm. Calculate the frequency and period of such waves (the solution of the problem for self-test is given on slide No. 21).
(Infrared radiation)
Lead #2.
Once in a distant kingdom, a terrible misfortune happened. Torrential rains flooded the harvest. A terrible famine threatened people. The king thought and instructed the three heroes to save people from misfortune, and to increase his own glory. The heroes gathered on the road. They rode and rode, and around the forest and swamps, ditches and cliffs. What have you not seen along the way? And so they drove out into an open field at the crossroads of three roads, where a stone lay. And on that stone there was an inscription: “If you go to the right, you will enter the infrared kingdom; if you go straight, you will enter the ultraviolet principality; If you go to the left, you will enter the realm of visible light.” And the good fellows dispersed along three paths: Alyosha Popovich - to the realm of visible light, Dobrynya Nikitich - to the ultraviolet principality, and Ilya Muromets - to the infrared kingdom.
Teacher:
Who are we following? We need to get to the IR-kingdom.
Students:
Follow Ilya Muromets to the infrared kingdom!
Host #2:
Ilya Muromets is walking along the path and does not see anything remarkable, but he feels that the heat is unbearable in this part of the spectrum, and there are no obvious and visible reasons for this!
Ilya Muromets:
I must have fallen into the zone of invisible radiation!
Host #2:
Suddenly a strong wind blew up, spun the hero and a voice was heard.
Why did you come to my kingdom? You won’t leave alive and you won’t collect bones until you solve my three riddles. The first question is: Who am I? Where are my relatives from?
Ilya Muromets:
Most visible light sources emit, in addition to visible rays, also rays invisible to our eyes. These are infrared rays. They are of the same nature as the visible ones. They are electromagnetic waves, the length of which is 3·10 -5 m. Any body, even a human one, can be their source. Emitters are atoms and molecules, or rather, electrons and ions (slide No. 22).
Fine! The second question is: "What are the properties of my behavior?"
Ilya Muromets:(simultaneously with the answer, slides with properties appear)
Infrared radiation has many properties: reflected from objects; bodies that are transparent to visible rays can be opaque to invisible light and vice versa; weakly scattered by the medium, as they have longer wavelengths than visible light; chemically inactive and used for film development; have a strong thermal effect (slide No. 23).
Where are my properties used?
Ilya Muromets:(simultaneously with the answer, slides with areas of application appear)
Infrared radiation is used in medicine for heating the tissues of a living organism; drying of various products; when pasteurizing products; for the protection of premises from fires; in night vision devices (slide No. 24).
Fine! I'm letting you go!
(visible radiation)
Lead #2.
And what happened to Alyosha Popovich? What adventures came his way? And the hero came to the realm of visible light. There is a hero and sees the light of unearthly beauty (garland).
Alesha Popovich:
Wow! Red! Orange! Yellow! Green! Blue! Blue! Violet! Oh holy spectrum! Oh, the magic number seven! (slide number 25) (meets a girl).
Young woman:
Good day to you, hero! Where are you heading?
Alesha Popovich:
I came to where the road took me. into the realm of visible light. The path was not close, do not let me die of thirst, give me clean and cool water to drink.
Young woman:
Try the juices produced by our company. Vitaminized juices - the right way to health! (they take out 7 glasses of water tinted in the colors of the spectrum *)
* Juices put in the order of the spectrum.
Alesha Popovich:
Oh, hostess, delicious juice! Tell me, mistress, how are things in your kingdom?
Young woman:(simultaneously with the answer, slides with the laws of light appear) (slides No. 26-28). And where is the use of this magical light, you know?
Alesha Popovich:
Coloring of various materials and objects; light music, television; photosynthesis in nature; photograph (slide number 29).
You can conduct a simple and very beautiful experience - an experiment with tourmaline crystals.
Let's take a rectangular plate of tourmaline and direct a beam of light from an electric lamp normally at it. The rotation of the plate around the beam will not cause any change in the light intensity, the light only acquires a greenish color. But the light wave acquired new properties.
These properties are revealed if a beam of light is forced to pass through a second identical tourmaline crystal located parallel to the first.
With identically directed axes of crystals, the light beam weakens even more. But if the second crystal is rotated, leaving the first motionless, then the light will be extinguished.
This can be explained by the fact that light is a transverse wave and in the beam of waves incident from a conventional source there are oscillations of various directions perpendicular to the direction of wave propagation. A tourmaline crystal has the ability to transmit light waves with vibrations lying in one specific plane. Tourmaline crystal transforms natural light into plane polarized.
(ultraviolet radiation)
Lead #2.
Meanwhile, Dobrynya Nikitich ended up in an ultraviolet principality. He walked for a long time, looking for this magical principality in order to ask the great prince, the chief ruler for help in a terrible trouble that happened on his land. So that the ruler of the ultraviolet principality would help him return the sun to the clear sky, and dry up all the fields and meadows on the Russian land, so that the people of misfortune - grief did not know, but lived in satiety. And he meets the clear sun on his way (meets the sun).
Sun.
Why did you come to my kingdom? What trouble brought you here?
Nikitich.
Trouble has befallen my state, terrible torrential rains have flooded the entire crop! Hunger threatens us unprecedented. Great ruler, help return the clear sun, and dry and warm the Russian land.
Sun.
Fine! You just have to tell me what you know about ultraviolet radiation.
Nikitich(slides #30-36).
Sun.
I am satisfied! Return to your homeland and do not be sad! Soon the sun will shine again in the sky!
(X-ray)
Lead #2.
Let's start the news show. C vodka incidents. In connection with sleet, the number of injuries associated with the human skeletal apparatus has increased. If you find yourself in such a situation, we advise you to contact our center, where experienced radiologists are waiting for you. I have some characteristics of the radiation used in the new center (slide show #37-42).
(Gamma radiation)
Lead #2.
The created center in no way affects the general radiation background in the city, which today is 15 microR/h. Let us turn to our specialists for a comment (slide show No. 43-48).
Teacher.
So our journey on the scale of electromagnetic waves has ended. I hope you enjoyed our little walk. We close the table that you filled out during our trip. Let's check how you understood and remembered the spectra of electromagnetic waves.
Conclusion. Conclusions.
Teacher.
Previously, all information about the Universe was obtained in the visible range using optical telescopes (slide No. 49). In the 20th century, it became possible to analyze data received in the radio range; for this, radio telescopes are used. Currently, the study of galaxies and other objects of the Universe is carried out in the infrared, ultraviolet, X-ray ranges using detectors installed on spaceships and satellites.
spacecraft made it possible to conduct studies of space objects in all wavelength ranges of electromagnetic radiation. On the slide (slide No. 50) there is a photograph of the growing moon, taken in gamma rays; the sun in x-rays; Milky Way in various ranges.
Conclusions:(slide number 51)
Studies of electromagnetic radiation are of great importance for clarifying our understanding of the structure of matter. Studies of infrared, visible and ultraviolet radiation helped to elucidate the structure of molecules and the outer electron shells of atoms; the study of x-ray radiation made it possible to establish the structure of the inner electron shells of atoms and the structure of crystals, and the radiation of gamma rays provides much valuable information about the structure of atomic nuclei.
The analysis of the information obtained in the entire spectrum of electromagnetic waves makes it possible to compose a more complete picture of the structure of objects in the Universe, thereby expanding the boundaries of knowledge of nature.
Test (slide No. 52) (Appendix No. 2).
1 option.
1. In what cases does the emission of electromagnetic waves occur?
1. An electron moves uniformly and in a straight line.
2. The electron moves uniformly accelerated and rectilinearly.
3. An electron moves uniformly in a circle.
Answers: A. only 1
B. only 2
V. only 3
G. 1, 2, 3
D. 2 and 3
2. Does electromagnetic radiation arise when electrons decelerate?
Answers: A. no
B. yes
3. Which of the following radiations are capable of being diffracted at the edge of an obstacle?
Answers: A. Radio waves
B. Visible radiation C. X-ray
4. What properties will electromagnetic waves of the following ranges show when they fall on the human body? Make a match.
1. Radio waves
2.X-ray range
3. Infrared
4.Ultraviolet range.
B. Heat the tissues.
5. What kind of electromagnetic waves has the lowest frequency?
Answers: A. X-ray
B. Ultraviolet
B. Visible light
G. Infrared
D. Radio waves
Option 2.
1. What kind of electromagnetic waves has the longest wavelength?
Answers: A. X-ray
B. Ultraviolet
B. Visible light
G. Infrared
D. Radio waves
2. How fast does an electromagnetic wave propagate in a vacuum?
Answers: A. 300 km/s
B. 300,000 km/s
B. 30,000 km/s
D. 3,000 km/s
3. What properties will electromagnetic waves of the following ranges detect when falling on the human body? Make a match.
1.X-ray range
2. Radio waves
3. Ultraviolet range
4. Infrared.
Answers: A. Cause reddening of the skin.
B. Heat the tissues.
B. Almost completely reflected
G. Pass through soft tissues
4. Which of the following radiations have the ability to interfere?
Answers: A. Radio waves
B. Visible radiation
B. X-ray
D. Everything except X-rays
E. All of the above radiation
5. Does electromagnetic radiation arise when a charge moves with acceleration?
Answers: A. Yes
B. No
Homework (slide number 53).
§23, Rymkevich -1137,1139.
Repetition of formulas on the topic "Quantum Theory" (call the student to the blackboard).
How are wavelength and frequency related?
Write down the Einstein equation.
Independent work (according to the problem book of G. Stepanova 10-11 cells) (Appendix No. 3).
1 option.
What is the energy of a photon of red light having a wavelength of 0.72 microns.
Determine the maximum kinetic energy of photoelectrons emitted from potassium when it is illuminated by rays with a wavelength of 345 nm. The work function of electrons from potassium is 2.26 eV.
Option 2.
The radiation consists of photons with an energy of 6.4 · 10 -19 J. Determine the frequency and wavelength of this radiation.
The work function of electrons from gold is 4.76 eV. Find the red photo effect border for gold.
Summing up (questions to students).
Was the lesson interesting? How?
Have you learned something new?
Would you like to conduct lessons in this form?
For the first time the hypothesis of the existence of electromagnetic waves was expressed in 1864 by the Scottish physicist James Maxwell. In his work, he showed that the sources of the electric field can be both electric charges, and magnetic fields that change with time. A change in the induction of the magnetic field over time causes the appearance of a vortex electric field in the surrounding space. Maxwell suggested that any change in the intensity of the vortex electric field is accompanied by the appearance of an alternating magnetic field. This again leads to the appearance of a vortex electric field, and so on. This process can be repeated "indefinitely" because the fields can alternately reproduce each other even in a vacuum.
- A set of interconnected periodically changing electric and magnetic fields is called electromagnetic field.
According to Maxwell's theory, an alternating electromagnetic field propagates in space with a finite speed.
- An electromagnetic field that propagates in a vacuum or in some medium over time at a finite speed is called electromagnetic wave.
Electromagnetic waves were experimentally discovered in 1887 by the German physicist Heinrich Rudolf Hertz. Hertz believed that such waves could not be used to transmit information. However, on May 7, 1905, the Russian scientist Alexander Stepanovich Popov carried out the world's first transmission of information by electromagnetic waves - a radio transmission and laid the foundation for the era of radio broadcasting.
Properties of electromagnetic waves
- Electromagnetic waves are transverse, since the speed \(\vec(\upsilon)\) of wave propagation, the strength \(\vec(E)\) of the electric field and the induction \(\vec(B)\) of the magnetic field of the wave are mutually perpendicular.
- Speed electromagnetic wave in vacuum (air):
\(c = \dfrac(1)(\sqrt(\varepsilon_(0) \cdot \mu_(0))),\)
where ε 0 is the electrical constant, μ 0 is the magnetic constant.
Velocity of propagation of electromagnetic waves in vacuum c= 3⋅10 8 m/s is the maximum (maximum) achievable value. In any substance, their propagation speed is less c and depends on its electrical and magnetic properties:
\(\upsilon = \dfrac(c)(\sqrt(\varepsilon \cdot \mu)),\)
Where ε is the dielectric constant of the medium, tabular value, μ is the magnetic permeability of the medium, tabular value.
- The propagation of electromagnetic waves is associated with the transfer of electromagnetic field energy in space. Bulk density transferred energy is equal to
\(\omega = \dfrac(\varepsilon \cdot \varepsilon_(0) \cdot E^(2))(2) + \dfrac(B^(2))(2 \mu \cdot \mu_(0)) ,\)
Where E- intensity vector modulus, B- modulus of the magnetic induction vector.
- Like other waves, electromagnetic waves can absorb, reflect, refract, experience interference and diffraction.
- electromagnetic wave exists without field sources in the sense that after its emission, the electromagnetic field of the wave becomes unrelated to the source. The emission of electromagnetic waves occurs when fast motion electric charges.
Electromagnetic wave scale
The properties of electromagnetic waves depend very strongly on their frequency. The spectrum of electromagnetic radiation is conveniently depicted using the scale of electromagnetic waves shown in Figure 2.
The classification of electromagnetic waves depending on the frequencies (wavelengths) is given in Table 1.
Table 1.
Classification of electromagnetic waves
| Types of radiation | Frequency interval, Hz | Wavelength interval, m | Radiation sources |
|---|---|---|---|
| low frequency waves | < 3·10 3 | > 1⋅10 5 | Alternators, electrical machines |
| radio waves | 3 10 3 – 3 10 9 | 1 10 5 – 1 10 –1 | Oscillating circuits, Hertz vibrators |
| Microwave | 3 10 9 – 1 10 12 | 1 10 –1 – 1 10 –4 | Lasers, semiconductor devices |
| Infrared radiation | 1 10 12 – 4 10 14 | 1 10 -4 - 7 10 -7 | Sun, electric lamps, lasers, cosmic rays |
| Visible radiation | 4 10 14 – 8 10 14 | 7 10 -7 - 4 10 -7 | Sun, electric lamps, fluorescent lamps, lasers |
| Ultraviolet radiation | 8 10 14 – 1 10 16 | 4 10 -7 - 3 10 -8 | Sun, cosmic rays, lasers, electric lamps |
| x-ray radiation | 1 10 16 – 3 10 20 | 3 10 -8 - 1 10 -12 | Betatrons, solar corona, celestial bodies, x-ray tubes |
| Gamma radiation | 3 10 20 – 3 10 29 | 1 10 -12 - 1 10 -21 | Cosmic radiation, radioactive decays, betatrons |
Currently, electromagnetic waves are widely used in science and technology:
- melting and hardening of metals in the electrical industry, the manufacture of permanent magnets ( low frequency waves);
- television, radio communication, radar ( radio waves);
- mobile communication, radar ( microwave);
- welding, cutting, melting of metals with lasers, night vision devices ( infrared radiation);
- lighting, holography, lasers ( visible radiation);
- luminescence in gas-discharge lamps, hardening of living organisms, lasers ( ultraviolet radiation);
- X-ray therapy, X-ray diffraction analysis, lasers ( x-rays);
- flaw detection, diagnostics and therapy in medicine, the study of the internal structure of atoms, lasers, military science ( gamma radiation).
Literature
Zhilko, V.V. Physics: textbook. allowance for grade 11 general education. school from Russian lang. training / V.V. Zhilko, L.G. Markovich. - Minsk: Nar. Asveta, 2009. - S. 57-58.
the formula for adding intensities should contain the average value cos δ . But this average value for one period of oscillations is equal to zero. Therefore, we get I = I 1 + I 2 , that is, the intensity of the wave when two beams are added is equal to the sum of the intensities of these beams, and there is no interference.
Note that the ability to interfere is the most important feature of the wave process and is the wave nature of light.
SCALE OF ELECTROMAGNETIC WAVES Electromagnetic waves are a continuous series of radiation
cheniya, extending from radio waves to γ-rays. The figure below shows the scale of electromagnetic waves.
1010 |
10 12 10 14 10 16 10 18 |
The numbers indicate the frequency ranges of electromagnetic waves:
1 - radio waves; 2 - infrared rays; 3 - visible light; 4 - ultraviolet rays; 5 - X-ray and γ - rays.
Visible light occupies a range of about 4 1014 to 8 1014 Hz. Visible white light is the sum of electromagnetic waves of different frequencies, each of which causes a sensation from red to purple as the frequency increases (so-called spectral colors: red, orange, yellow, green, cyan, indigo and violet).
White light interference produces color maxima because each frequency has its own maximum interference condition. An example is the play of colors on thin films and CDs.
The propagation of white light in many cases can be considered by abstracting from its wave nature and assuming that the light propagates along straight lines called rays. It is thanks to the ray of light that humanity has formed the concept of a straight line. The wave nature of light is due to the wavelength. Assuming that in the limit the wavelength λ → ∞, one can quite strictly explain the reflection and refraction of light, the formation of a shadow, and other phenomena that are studied by geometric optics. Thus the condition λ → ∞ is approximation of geometric optics.
In the approximation of geometric optics, the light behind the barrier should not penetrate into the region of the geometric shadow. In reality, the light wave propagates throughout space, penetrating into the region of the geometric shadow. This penetration is the greater, the smaller the size of the barrier or hole. If the size of the barrier or hole is comparable to the wavelength, the geometrical optics approximation is unacceptable. Wave optics comes into play. The condition λ ≥ R , where R is the size of the barrier or hole, is wave optics approximation. Deviations from the law of rectilinear propagation of light and related phenomena are called diffraction.
At sufficiently short wavelengths, light can exhibit its own
quantum, corpuscular, properties. Condition λ ≤ hc , h is a constant
E since
Planck, and Epor is the threshold energy, is quantum optics approximation. The quantum properties of light will be discussed in the next part of the lectures.