Note 32. Electromagnetic waves (EMW).
3. Electromagnetic waves
Definition. Electromagnetic field– a form of matter, which is a system of alternating electric and magnetic fields that mutually generate each other.
Definition. Electromagnetic wave (EMW)– an electromagnetic field that propagates in space over time.
Examples of emitters of electromagnetic waves: an oscillatory circuit (the main element of a radio transmitter/receiver), the sun, a light bulb, an X-ray machine, etc.
Comment. Heinrich Hertz experimentally confirmed the existence of electromagnetic waves, using oscillatory circuits tuned to resonance (Hertz vibrator) to receive and transmit electromagnetic waves.
Basic properties of EMW:
1) The speed of propagation of electromagnetic waves in a vacuum is the speed of light;
2) EMF is a transverse wave, the vectors of tension, magnetic induction and propagation speed are mutually perpendicular; 
3) If electromagnetic waves are emitted by an oscillatory circuit, then its period and frequency coincide with the oscillation frequency of the circuit;
4) As for all waves, the length of the electromagnetic wave is calculated using the formula.
Electromagnetic wave scale :
| Range name | Description | Use in technology |
| Low frequency radiation | Radiation sources, usually AC devices | No areas of mass application |
| Radio waves | Emitted by various radio transmitters: mobile phones, radars, television and radio stations, etc.When propagating, long radio waves can bend around the earth's surface, short ones are reflected from the Earth's ionosphere, and ultrashort ones pass through the ionosphere | Used to transmit information: television, radio, Internet, mobile communications, etc. |
| Infrared radiation | All bodies are sources, and the higher the body temperature, the higher the radiation intensity. In almost the entire spectrum it is a carrier of thermal radiation |
Night vision devices, thermal imagers, infrared heaters, low-speed communication channels |
| Visible light | Emitted by lighting fixtures, stars, etc. Wavelength range λ∈(380 nm; 700 nm). Human eyes are sensitive to the perception of this radiation. Different frequencies (wavelengths) are perceived by humans as different colors - from red to violet |
Photo and video recording equipment, microscopes, binoculars, telescopes, etc. |
| Ultraviolet radiation | Main sources: Sun, ultraviolet lamps. It affects human skin in such a way that in moderate doses it promotes the production of melanin pigment and darkening of the skin, and at high intensity it leads to burns. Promotes the production of vitamin D in human skin. |
Disinfection of water and air, security authentication devices, solariums |
| X-ray radiation | The main sources are X-ray tubes, in which rapid deceleration of charged particles occurs. X-rays can penetrate matter. Harmful to living organisms if exposed to excessive radiation |
X-ray, fluorography, inspection of things at airports, etc. |
| γ – radiation | As a rule, it is one of the products of nuclear reactions. This is one of the most high-energy and penetrating radiations. Is harmful and dangerous to living organisms |
Flaw detection of products, radiation therapy, sterilization, food preservation |
Definition. Radar– detection and determination of the location of various objects using radio waves. It is based primarily on the properties of reflection of radio waves.
Comment. For radar, a device is used, which is usually called a radar; its main elements are a transmitter and a receiver. 
– distance to the object in radar, m
Where t– signal travel time to the target and back, s
c– speed of light, m/s
Comment. The principle of radar is similar to the principle of echolocation (see abstract No. 30).
Limitations in target detection range and one-way signal transmission:
1) The maximum target detection range depends on the time interval between two consecutive radar pulses ():
– maximum radar distance, m
2) The minimum target detection range depends on the duration of the radar pulse ():
– minimum radar distance, m
3) The signal transmission range is limited by the shape of the Earth;
4) The signal transmission range is limited by the power of the radio transmitter and the sensitivity of the receiving antenna: 
– minimum signal power that the antenna can receive (sensitivity), W
Where is the transmitter power, W
S – surface area of the receiving antenna, m²
R – distance from the transmitter to the antenna, m
Comment. In points 1-3, when determining the signal propagation range, it is not taken into account that the power of the transmitting antenna and the sensitivity of the receiving antenna are limited.
"Electromagnetic waves".
Lesson objectives:
Educational:
- introduce students to the features of the propagation of electromagnetic waves;
- consider the stages of creating the theory of the electromagnetic field and experimental confirmation of this theory;
Educational: introduce students to interesting episodes from the biography of G. Hertz, M. Faraday, Maxwell D.K., Oersted H.K., A.S. Popova;
Developmental: 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 creating the theory of the electromagnetic field and experimental confirmation of this theory, and dwell on some biographical data.
Repetition.
To achieve 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 a wave? (wavelength, wave speed, oscillation period and oscillation frequency)
What is the mathematical relationship between wavelength and oscillation period? (wavelength is equal to the product of wave speed and oscillation period)
Learning new material.
An electromagnetic wave is in many ways similar to a mechanical wave, but there are also differences. The main difference is that this wave does not require a medium to propagate. An electromagnetic wave is the result of the propagation of an alternating electric field and an alternating magnetic field in space, i.e. electromagnetic field.
The electromagnetic field is created by accelerated moving charged particles. Its presence is relative. This is a special type of matter, which is a combination of variable electric and magnetic fields.
An electromagnetic wave is the propagation of an electromagnetic field in space.
Consider the graph of the propagation of an electromagnetic wave.
The propagation diagram of an electromagnetic wave is shown in the figure. It is necessary to remember that the vectors of electric field strength, magnetic induction and wave propagation speed are mutually perpendicular.
Stages of creating the theory of an electromagnetic wave and its practical confirmation.
Hans Christian Oersted (1820) Danish physicist, permanent secretary of the Royal Danish 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, and molecular physics.
In 1820, he discovered the effect of 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. He experimentally studied the compressibility and elasticity of liquids and gases and invented the piezometer (1822). Conducted research on acoustics, in particular tried to detect the occurrence of electrical phenomena due to sound. Investigated deviations from the Boyle-Mariotte law.
Ørsted was a brilliant lecturer and popularizer, organized the Society for the Propagation of Natural Science in 1824, created Denmark's first physics laboratory, and contributed to improving the teaching of physics in the country's educational institutions.
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 a primary education, and then, due to life’s problems, I worked and simultaneously studied popular science literature on physics and chemistry. Later, Faraday became a laboratory assistant for a famous 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 an electric field creates a magnetic field. After pondering this phenomenon, Faraday set out to create an electric field from a magnetic field and carried a magnet in his pocket as a constant reminder. Ten years later, he put his motto into practice. Turned magnetism into electricity: creates a magnetic field - electric current
The theoretical scientist derived the equations that bear his name. These equations said that alternating magnetic and electric fields create each other. From these equations it follows that an alternating magnetic field creates a vortex electric field, which creates an alternating magnetic field. In addition, in his equations there was a constant value - this is the speed of light in a vacuum. Those. from this theory it followed that an electromagnetic wave propagates in space at the speed of light in a vacuum. The truly brilliant work was appreciated by many scientists of that time, and A. Einstein said that the most fascinating thing during his studies was Maxwell’s theory.
Heinrich Hertz (1887)
Heinrich Hertz was born a sickly child, but became a very smart student. He liked all the subjects he studied. The future scientist loved to write poetry and work on a lathe. After graduating from high school, Hertz entered a higher technical school, but did not want to be a narrow specialist and entered the University of Berlin to become a scientist. After entering the university, Heinrich Hertz sought to study in a physics laboratory, but for this it was necessary to solve competitive problems. And he set about solving the following problem: does electric current have kinetic energy? This work was designed to take 9 months, but the future scientist solved it in three months. True, a negative result is incorrect from a modern point of view. The measurement accuracy had to be increased thousands of times, which was not possible at that time.
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 that is called today an antenna and, with the help of transmitting and receiving antennas, created and received electromagnetic waves 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 light in 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. First my eyes failed, then my ears, teeth and nose started to hurt. He died soon after.
Heinrich Hertz completed the enormous work begun by Faraday. Maxwell transformed Faraday's ideas into mathematical formulas, and Hertz transformed mathematical images into visible and audible electromagnetic waves. Listening to the radio, watching television programs, we must remember this person. It is no coincidence that the unit of oscillation frequency is named after Hertz, and it is not at all accidental that the first words conveyed by the Russian physicist A.S. Popov using wireless communication 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 the Gulf of Finland. In 1901, the Italian engineer G. Marconi carried out radio communications across the Atlantic Ocean.
Let's watch a video clip that discusses some of the properties of an electromagnetic wave. After viewing we will answer questions.
Why does the light bulb in the receiving antenna change its intensity when a metal rod is inserted?
Why doesn't this happen when replacing a metal rod with a glass rod?
Consolidation.
Answer the questions:
What is an electromagnetic wave?
Who created the theory of electromagnetic waves?
Who studied the properties of electromagnetic waves?
Fill out the answer table in your notebook, marking the question number.
How does wavelength depend on vibration frequency?
(Answer: Inversely proportional)
What will happen to the wavelength if the period of particle oscillation doubles?
(Answer: Will increase by 2 times)
How will the oscillation frequency of the radiation change when the wave passes into a denser medium?
(Answer: Will not change)
What causes electromagnetic wave emission?
(Answer: Charged particles moving with acceleration)
Where are electromagnetic waves used?
(Answer: cell phone, microwave, television, radio broadcast, etc.)
(Answers to questions)
Homework.
It is necessary to prepare reports on various types of electromagnetic radiation, listing their features and talking about their application in human life. The message must be five minutes long.
- Types of electromagnetic waves:
- Sound Frequency Waves
- Radio waves
- Microwave radiation
- Infrared radiation
- Visible light
- Ultraviolet radiation
- X-ray radiation
- Gamma radiation
Summarizing.
Literature.
- Kasyanov V.A. Physics 11th grade. - M.: Bustard, 2007
- Rymkevich A.P. Collection of problems in physics. - M.: Enlightenment, 2004.
- Maron A.E., Maron E.A. Physics 11th grade. 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 book, - M., 1983
Municipal budgetary educational institution -
secondary school No. 6 named after. Konovalova V.P.
Klintsy, Bryansk region
Developed by a physics teacher of the first qualification category:
Sviridova Nina Grigorievna.
Goals and objectives:
Educational:
Introduce the concept of electromagnetic field and electromagnetic wave;
Continue to form correct ideas about the physical picture of the world;
Study the process of formation of an electromagnetic wave;
Study the types of electromagnetic radiation, their properties, application and effect on the human body;
Introduce the history of the discovery of electromagnetic waves
Develop skills in solving qualitative and quantitative problems.
Educational:
Development of analytical and critical thinking (ability to analyze natural phenomena, experimental results, ability to compare and establish common and distinctive features, ability to examine tabular data, ability to work with information)
Student speech development
Educational
Cultivating cognitive interest in physics, a positive attitude towards knowledge, and respect for health.
Equipment: presentation; table “Scale of electromagnetic waves”, worksheet with tasks for independent educational work, physical equipment.
Demonstration experiments and physical equipment.
1) Oersted's experiment (current source, magnetic needle, conductor, connecting leads, key)
2) the effect of a magnetic field on a conductor with current (current source, arc-shaped magnet, conductor, connecting leads, key)
3) the phenomenon of electromagnetic induction (coil, strip magnet, demonstration galvanometer)
Intersubject connections
Mathematics (solving calculation problems);
History (a little about the discovery and research of electromagnetic radiation);
Life Safety (rational and safe use of devices that are sources of electromagnetic radiation);
Biology (effect of radiation on the human body);
Astronomy (electromagnetic radiation from space).
1. Motivational stage -7 min.
Press conference “Electricity and Magnetism”
Teacher: The modern world surrounding people is filled with a wide variety of technology. Computers and mobile phones, televisions have become our closest indispensable assistants and even replace our communication with friends. Numerous studies show that our assistants at the same time take away our most valuable thing - our health. Do your parents often wonder what causes more damage: a microwave oven or a cell phone?
We will answer this question later.
Now - a press conference on the topic “Electricity and Magnetism”.
Students. Journalist: Electricity and magnetism, known since antiquity, were considered phenomena unrelated to each other until the beginning of the 19th century and were studied in different branches of physics.
Journalist: Outwardly, electricity and magnetism manifest themselves in completely different ways, but in fact they are closely related, and many scientists have seen this connection. Give an example of analogies, or general properties of electrical and magnetic phenomena.
Expert - physicist.
For example, attraction and repulsion. In the electrostatics of unlike and like charges. In the magnetism of opposite and like poles.
Journalist:
The development of physical theories has always occurred on the basis of overcoming contradictions between hypothesis, theory and experiment.
Journalist: At the beginning of the 19th century, the French scientist Francois Arago published the book “Thunder and Lightning”. Does this book contain some very interesting entries?
Here are some excerpts from the book Thunder and Lightning: “...In June 1731, a merchant placed in the corner of his room in Wexfield a large box filled with knives, forks and other objects made of iron and steel... Lightning penetrated the house right through the corner in which the box stood, broke it and scattered all the things that were in it. All these forks and knives... turned out to be highly magnetized...")
What hypothesis could physicists put forward after analyzing excerpts from this book?
Expert - physicist: Objects were magnetized as a result of a lightning strike, at that time lightning was known to be an electric current, but scientists at that time could not explain why this happened theoretically.
Slide No. 10
Journalist: Experiments with electric current attracted scientists from many countries.
An experiment is a criterion for the truth of a hypothesis!
What experiments of the 19th century showed the connection between electrical and magnetic phenomena?
Expert - physicist. Demonstration experiment - Oersted's experiment.
In 1820, Oersted conducted the following experiment (Oersted's experiment, a magnetic needle turns near a conductor with current) There is a magnetic field in the space around the conductor with current.
In the absence of equipment, the demonstration experience can be replaced by the TsOR
Journalist. Oersted experimentally proved that electrical and magnetic phenomena are interrelated. Was there a theoretical basis?
Expert - physicist.
The French physicist Ampere in 1824 Ampere conducted a series of experiments and studied the effect of a magnetic field on current-carrying conductors.
Demonstration experiment - the effect of a magnetic field on a current-carrying conductor.
Ampere was the first to combine two previously separate phenomena - electricity and magnetism - with one theory of electromagnetism and proposed to consider them as the result of a single natural process
Teacher: a problem has arisen: The theory has been met with distrust by many scientists!?
Expert physicist. Demonstration experiment - the phenomenon of electromagnetic induction (coil at rest, magnet moving).
In 1831, the English physicist M. Faraday discovered the phenomenon of electromagnetic induction and found out that the magnetic field itself is capable of generating electric current.
Journalist. Problem: We know that current can occur in the presence of an electric field!
Expert - physicist. Hypothesis: The electric field arises as a result of a change in the magnetic field. But there was no proof of this hypothesis at that time.
Journalist: By the middle of the 19th century, quite a lot of information had accumulated about electrical and magnetic phenomena?
This information required systematization and integration into a single theory; who created this theory?
Expert physicist. This theory was created by the outstanding English physicist James Maxwell. Maxwell's theory resolved a number of fundamental problems in electromagnetic theory. Its main provisions were published in 1864 in the work “Dynamic Theory of the Electromagnetic Field”
Teacher: Guys, what will we study in the lesson, formulate the topic of the lesson.
Students formulate the topic of the lesson.
Teacher: Write down the topic of the lesson on the worksheet that we will work with during the lesson today.
|
Lesson summary worksheet for 9th grade student…………………………………………………………… Lesson topic:……………………………………………………………………………………………………………………………………… ……………. 1) The alternating electric and magnetic fields generating each other form a single…………………………………………………………………………………………………………… ……………………………………………………………… 2) Sources of electromagnetic field -………………….…………………charges, moving with …………………………………………………………… 3)Electromagnetic wave………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………. ……………………………………………………………………………………….................. 4) Electromagnetic waves propagate not only in matter, but also in …………………………….. 5) Wave type -………………………………………… 6) The speed of electromagnetic waves in a vacuum is denoted by the Latin letter c: with ≈……………………………………………………… The speed of electromagnetic waves in matter………………….than in vacuum………… 7) Wavelength λ=…………………………………………………………… |
What would you like to learn in class, what goals will you set for yourself?
Students formulate the goals of the lesson.
Teacher: Today in the lesson we will learn what an electromagnetic field is, expand our knowledge about the electric field, get acquainted with the process of the occurrence of an electromagnetic wave and some properties of electromagnetic waves,
2.Updating basic knowledge - 3 min.
Frontal survey
1. What is a magnetic field?
2. What generates a magnetic field?
3. How is the magnetic induction vector designated? Name the units of measurement of magnetic induction.
4.What is an electric field. Where does the electric field exist?
5. What is the phenomenon of electromagnetic induction?
6. What is a wave? What are the types of waves? What wave is called transverse?
7. Write down the formula for calculating the wavelength?
3. Operational-cognitive stage - 25 min
1)Introduction of the concept of electromagnetic field
According to Maxwell's theory, alternating electric and magnetic fields cannot exist separately: a changing magnetic field generates an alternating electric field, and a changing electric field generates an alternating magnetic field. These alternating electric and magnetic fields generating each other form a single electromagnetic field.
Working with the textbook - reading the definition p. 180
Definition from the textbook: Any change in the magnetic field over time leads to the emergence of an alternating electric field, and any change in the electric field over time generates an alternating magnetic field.
ELECTROMAGNETIC FIELD
These alternating electric and magnetic fields generating each other form a single electromagnetic field.
Working with a plan-note (students supplement the notes in the process of learning new material).
1) Variable electric and magnetic fields generating each other form a single ………………… (electromagnetic field)
2) Sources of electromagnetic field -……(electric) charges moving with…………………(acceleration)
Source of electromagnetic field. Textbook page 180
Sources of electromagnetic field can be:
Electric charge moving with acceleration, for example oscillating (the electric field they create changes periodically)
(unlike a charge moving at a constant speed, for example, in the case of a direct current in a conductor, a constant magnetic field is created here).
Qualitative task.
What field appears around an electron if:
1) the electron is at rest;
2) moves at a constant speed;
3) is it moving with acceleration?
An electric field always exists around an electric charge, in any reference system, a magnetic field exists in the one relative to which the electric charges move,
An electromagnetic field is in a reference frame relative to which electric charges move with acceleration.
2) Explanation of the mechanism of occurrence of induction current, e in the case when the conductor is at rest. (Solving the problem formulated at the motivational stage during a press conference)
1) An alternating magnetic field generates an alternating electric field (vortex), under the influence of which free charges begin to move.
2) The electric field exists regardless of the conductor.
Problem: is the electric field created by an alternating magnetic field different from the field of a stationary charge?
3) Introducing the concept of tension, describing the lines of force of the electric field, electrostatic and vortex, highlighting the differences. (Solving the problem formulated at the motivational stage during a press conference)
Introduction of the concept of intensity and lines of force of an electrostatic field.
What can you say about electrostatic field lines?
How does an electrostatic field differ from a vortex electric field?
The vortex field is not associated with the charge, the lines of force are closed. Electrostatic is associated with a charge, vortex is generated by an alternating magnetic field and is not associated with a charge. The general one is an electric field.
4)Introduction of the concept of electromagnetic wave. Distinctive properties of electromagnetic waves.
According to Maxwell's theory, an alternating magnetic field generates an alternating electric field, which in turn generates a magnetic field, as a result of which the electromagnetic field propagates in space in the form of a wave.
Maintaining 3 definitions, first 2), then students read the definition in the textbook, page 182, write down the definition in the notes that you consider easier to remember or the one you liked.
3)Electromagnetic wave…………….
1) is a system of variable (vortex) electric and magnetic fields generating each other and propagating in space.
2) this is an electromagnetic field propagating in space with a finite speed depending on the properties of the medium.
3) A disturbance in the electromagnetic field propagating in space is called an electromagnetic wave.
Properties of electromagnetic waves.
How are electromagnetic waves different from mechanical waves? See the textbook on page 181 and add the notes to paragraph 4.
4) Electromagnetic waves propagate not only in matter, but also in……(vacuum)
If a mechanical wave propagates, then vibrations are transmitted from particle to particle.
What makes an electromagnetic wave oscillate? For example, in a vacuum?
What physical quantities change periodically in it?
Tension and magnetic induction change over time!
How are vectors E and B oriented relative to each other in an electromagnetic wave?
Is the electromagnetic wave longitudinal or transverse?
5) wave type………(transverse)
Animation "Electromagnetic wave"
Speed of electromagnetic waves in vacuum. Page 181 - find the numerical value of the speed of electromagnetic waves.
6) The speed of electromagnetic waves in vacuum is denoted by the Latin letter c: c ≈ 300,000 km/s=3*108 m/s;
What can be said about the speed of electromagnetic waves in matter?
The speed of electromagnetic waves in matter……(smaller) than in vacuum.
In a time equal to the oscillation period, the wave has moved a distance along the axis equal to the wavelength.
For electromagnetic waves, the same relationships between wavelength, speed, period and frequency apply as for mechanical waves. Speed is designated by the letter c.
7) wavelength λ= c*T= c/ ν.
Let's repeat and check the information about electromagnetic waves. Students compare notes on the worksheets and on the slide.
Teacher: Any theory in physics must coincide with experiment.
Message learning. Experimental discovery of electromagnetic waves.
In 1888, the German physicist Heinrich Hertz experimentally obtained and recorded electromagnetic waves.
As a result of Hertz's experiments, all the properties of electromagnetic waves theoretically predicted by Maxwell were discovered!
5) Study of the scale of electromagnetic radiation.
Electromagnetic waves are divided by wavelength (and, accordingly, by frequency) into six ranges: the boundaries of the ranges are very arbitrary.
Electromagnetic wave scale
Low frequency radiation.
1.Radio waves
2. Infrared radiation (thermal)
3.Visible radiation (light)
4.Ultraviolet radiation
5. X-rays
6.γ - radiation
Teacher: What information can be obtained if you examine the scale of electromagnetic waves.
Students: From the pictures you can determine which bodies are sources of waves or where electromagnetic waves are used.
Conclusion: We live in a world of electromagnetic waves.
What bodies are sources of waves.
How do the wavelength and frequency change if we go on a scale from radio waves to gamma radiation?
Why do you think this table shows space objects as examples?
Students: Astronomical objects (stars, etc.) emit electromagnetic waves.
Research and comparison of information on electromagnetic wave scales.
Compare 2 scales on a slide? What is the difference? What radiation is not on the second scale?
Why are there no low-frequency oscillations on the second one?
Student message.
Maxwell: to create an intense electromagnetic wave that could be recorded by a device at some distance from the source, it is necessary that the oscillations of the tension and magnetic induction vectors occur at a sufficiently high frequency (about 100,000 oscillations per second or more). The frequency of the current used in industry and everyday life is 50 Hz.
Give examples of bodies emitting low-frequency radiation.
Student message.
The influence of low-frequency electromagnetic radiation on the human body.
Electromagnetic radiation with a frequency of 50 Hz, which is created by AC power cables, causes
Fatigue,
Headache,
Irritability,
Fatigue,
Memory loss
Sleep disturbance…
Teacher: Please note that memory deteriorates if you work with a computer for a long time or watch TV, which prevents us from studying well. Let's compare the permissible standards for electromagnetic radiation from household appliances, electric vehicles, etc. Which electrical appliances are more harmful to human health? What is more dangerous: a microwave oven or a cell phone? Does the power depend on the power of the device?
Student message. Rules to help you stay healthy.
1) The distance between electrical appliances must be at least 1.5-2 m. (So as not to increase the effect of household electromagnetic radiation)
Your beds should be the same distance away from the TV or computer.
2) stay as far away from sources of electromagnetic fields as possible and for as little time as possible.
3) Unplug all devices that are not working.
4) Turn on as few devices as possible at the same time.
Let's explore another 2 scale of electromagnetic waves.
What radiation is present on the second scale?
Students: On the second scale, there is microwave radiation, but on the first there is not.
Although the frequency range is notional, do microwave waves belong to radio waves or infrared radiation, if we consider scale No. 1?
Students: Microwave radiation - radio waves.
Where are microwave waves used?
Student message.
Microwave radiation is called ultra-high frequency (microwave) radiation because it has the highest frequency in the radio range. This frequency range corresponds to wavelengths from 30 cm to 1 mm; therefore it is also called the decimeter and centimeter wave range.
Microwave radiation plays a big role in the life of a modern person, because we cannot refuse such achievements of science: mobile communications, satellite television, microwave ovens or microwave ovens, radar, the principle of operation of which is based on the use of microwaves.
Solving the problematic question posed at the beginning of the lesson.
What do a microwave oven and a cell phone have in common?
Students. The principle of operation is not based on the use of microwave radio waves.
Teacher: Interesting information about the invention of the microwave oven can be found on the Internet - homework.
Teacher: We live in a “sea” of electromagnetic waves, which is emitted by the sun (the entire spectrum of electromagnetic waves) and other space objects - stars, galaxies, quasars, we must remember that any electromagnetic radiation can, does bring both benefit and harm. The study of electromagnetic wave scales shows us how great the importance of electromagnetic waves is in human life.
6) Independent training work - work in pairs with a textbook pp. 183-184 and based on life experience. 5 test questions are mandatory for everyone, task 6 is a calculation problem.
1.The process of photosynthesis occurs under the influence
B) visible radiation-light
2.Human skin tans when exposed to
A) ultraviolet radiation
B) visible radiation-light
3. In medicine, fluorographic examinations are used
A) ultraviolet radiation
B) x-rays
4.For television communication they use
A) radio waves
B) x-rays
5. To avoid getting a retinal burn from solar radiation, people use glass “sunglasses”, since glass absorbs a significant part
A) ultraviolet radiation
B) visible radiation-light
6. At what frequency do ships transmit the SOS distress signal if, according to international agreement, the radio wave length should be 600m? The speed of propagation of radio waves in air is equal to the speed of electromagnetic waves in vacuum 3*108 m/s
4) Reflective-evaluative stage. Lesson summary -4.5 min
1) Checking independent work with self-assessment. If all test tasks are completed - grade “4”, if students managed to complete the task - “5”
Given: λ = 600 m, s = 3*108 m/s
Solution: ν = s/λ = 3*10^8 \ 600 = 0.005 * 10^8 = 0.5 * 10^6 Hz== 5 * 10^5 Hz
Answer: 500,000 Hz = 500 kHz = 0.5 MHz
2) Summing up and assessment and self-assessment of students.
What is an electromagnetic field?
What is an electromagnetic wave?
What do you now know about electromagnetic waves?
What is the significance of the material you studied in your life?
What did you like most about the lesson?
5. Homework - 0.5 min P. 52.53 exercises. 43, ex. 44(1)
The history of the invention of the microwave-Internet.
Lesson objectives:
Lesson type:
Form: lecture with presentation
Karaseva Irina Dmitrievna, 17.12.2017
2940 306
Development content
Lesson summary on the topic:
Types of radiation. Electromagnetic wave scale
Lesson developed
teacher of the LPR State Institution “LOUSOSH No. 18”
Karaseva I.D.
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 influence of various types of radiation on humans; systematize material on the topic and deepen students’ knowledge about electromagnetic waves; develop students’ oral speech, students’ creative skills, logic, memory; cognitive abilities; to develop students’ interest in studying physics; cultivate accuracy and hard work.
Lesson type: lesson in the formation of new knowledge.
Form: lecture with presentation
Equipment: computer, multimedia projector, presentation “Types of radiation.
Electromagnetic wave scale"
During the classes
Organizing time.
Motivation for educational and cognitive activities.
The Universe is an ocean of electromagnetic radiation. People live in it, for the most part, without noticing the waves permeating the surrounding space. While 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, humanity during the 20th century has mastered and put into its service its most varied types.
Setting the topic and goals 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. Write down the topic of the lesson: “Types of radiation. Electromagnetic wave scale" (Slide 1)
We will study each radiation according to the following generalized plan (Slide 2).Generalized plan for studying radiation:
1. Range name
2. Wavelength
3. Frequency
4. Who was it discovered by?
5. Source
6. Receiver (indicator)
7. Application
8. Effect on humans
As you study the topic, you must complete the following table:
Table "Electromagnetic radiation scale"
| Name radiation | Wavelength | Frequency | Who was open | Source | Receiver | Application | Effect on humans |
Presentation of new material.
(Slide 3)
The length of electromagnetic waves can be very different: from values of the order of 10
13
m (low frequency vibrations) up to 10
-10
m (
-rays). Light makes up a tiny part of the broad spectrum of electromagnetic waves. However, it was during the study of this small part of the spectrum that other radiations with unusual properties were discovered.
It is customary to highlight low frequency radiation, radio radiation, infrared rays, visible light, ultraviolet rays, x-rays and
-radiation. The shortest wavelength -radiation is emitted by atomic nuclei.
There is no fundamental difference between individual radiations. All of them are electromagnetic waves generated by charged particles. Electromagnetic waves are ultimately detected by their effect on charged particles . In a vacuum, radiation of any wavelength travels at a speed of 300,000 km/s. The boundaries between individual regions of the radiation scale are very arbitrary.
(Slide 4)
Radiation of different wavelengths differ from each other in the way they are receiving(antenna radiation, thermal radiation, radiation during braking of fast electrons, etc.) and registration methods.
All of the listed types of electromagnetic radiation are also generated by space objects and are successfully studied using rockets, artificial Earth satellites and spacecraft. First of all, this applies to X-ray and - radiation strongly absorbed by the atmosphere.
Quantitative differences in wavelengths lead to significant qualitative differences.
Radiations of different wavelengths differ greatly from each other in their absorption by matter. Short-wave radiation (X-ray and especially -rays) are weakly absorbed. Substances that are opaque to optical waves are transparent to these radiations. The reflection coefficient of electromagnetic waves also depends on the wavelength. But the main difference between long-wave and short-wave radiation is that short-wave radiation reveals the properties of particles.
Let's consider each radiation.
(Slide 5)
Low frequency radiation occurs in the frequency range from 3 10 -3 to 3 10 5 Hz. This radiation corresponds to a wavelength of 10 13 - 10 5 m. Radiation of such relatively low frequencies can be neglected. The source of low-frequency radiation is alternating current generators. Used in melting and hardening of metals.
(Slide 6)
Radio waves occupy the frequency range 3·10 5 - 3·10 11 Hz. They correspond to a wavelength of 10 5 - 10 -3 m. Source radio waves, just like Low frequency radiation is alternating current. Also the source is a radio frequency generator, stars, including the Sun, galaxies and metagalaxies. The indicators are a Hertz vibrator and an oscillatory circuit.
High frequency radio waves, compared to low-frequency radiation leads to noticeable emission of radio waves into space. This allows them to be used to transmit information over various distances. Speech, music (broadcasting), telegraph signals (radio communications), and images of various objects (radiolocation) 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 radiometeorology, processes are studied based on the characteristics of received waves.
(Slide 7)
Infrared radiation occupies the frequency range 3 10 11 - 3.85 10 14 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. While studying the temperature rise of a thermometer heated by visible light, Herschel discovered the greatest heating of the thermometer outside the region of visible light (beyond 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 share (from 70 to 80%) of the radiation energy of incandescent lamps with tungsten filament. Infrared radiation is emitted by 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 photos and thermistors, special photo emulsions. Infrared radiation is used for drying wood, food and various paints and varnishes (infrared heating), for signaling in poor visibility, and makes it possible to use optical devices that allow you to see in the dark, as well as for remote control. Infrared rays are used to guide projectiles and missiles to targets and to detect camouflaged enemies. These rays make it possible to determine the difference in temperatures of individual areas of the surface of the planets, the structural features of the molecules of matter (spectral analysis). Infrared photography is used in biology when studying plant diseases, in medicine when diagnosing skin and vascular diseases, and in forensics when detecting counterfeits. When exposed to humans, it causes an increase in the temperature of the human body.
(Slide 8)
Visible radiation - the only range of electromagnetic waves perceived by the human eye. Light waves occupy a fairly narrow range: 380 - 670 nm ( = 3.85 10 14 - 8 10 14 Hz). The source of visible radiation is valence electrons in atoms and molecules, changing their position in space, as well as free charges, moving quickly. This part of the spectrum gives a person maximum information about the world around him. In terms of its physical properties, it is similar to other spectral ranges, being only a small part of the spectrum of electromagnetic waves. Radiation having different wavelengths (frequencies) in the visible range has different physiological effects on the retina of the human eye, causing the 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. Approximately, we can name seven primary colors distinguished by the human eye in the visible range (in order of increasing frequency of radiation): red, orange, yellow, green, blue, indigo, violet. Memorizing the sequence of the primary colors of the spectrum is facilitated by a 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 influence the occurrence of chemical reactions in plants (photosynthesis) and in animals and humans. Visible radiation is emitted by certain 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 helps maintain biological life on Earth. Visible radiation is also 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.
(Slide 9)
Ultraviolet radiation, electromagnetic radiation invisible to the eye, occupying the spectral region between visible and x-ray radiation within wavelengths of 3.8 ∙ 10 -7 - 3 ∙ 10 -9 m ( = 8 * 10 14 - 3 * 10 16 Hz). Ultraviolet radiation was discovered in 1801 by the German scientist Johann Ritter. By studying the blackening of silver chloride under the influence of visible light, Ritter discovered that silver blackens even more effectively in the region beyond the violet end of the spectrum, where visible radiation is absent. The invisible radiation that caused this blackening was called ultraviolet radiation.
The source of ultraviolet radiation is the valence electrons of atoms and molecules, as well as rapidly moving free charges.
Radiation from solids heated to temperatures of -3000 K contains a noticeable proportion of ultraviolet radiation of a 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 of 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-wave part of their radiation ( 290 nm) reaches the earth's surface. To register ultraviolet radiation at
= 230 nm, conventional photographic materials are used; in the shorter wavelength region, special low-gelatin photographic layers are sensitive to it. Photoelectric receivers are used that use the ability of ultraviolet radiation to cause ionization and the photoelectric effect: photodiodes, ionization chambers, photon counters, photomultipliers.
In small doses, ultraviolet radiation has a beneficial, healing effect on humans, activating the synthesis of vitamin D in the body, as well as causing tanning. A large dose of ultraviolet radiation can cause skin burns and cancer (80% curable). In addition, excessive ultraviolet 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 used in fluorescent lamps, in forensic science (fraudulent documents can be detected from photographs), and in art history (with the help of ultraviolet rays, invisible traces of restoration can be detected in paintings). Window glass practically does not transmit ultraviolet radiation, because 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 a room with the window closed.
The human eye does not see ultraviolet radiation because... The cornea of the eye and the eye lens absorb ultraviolet radiation. Ultraviolet radiation is visible to some animals. For example, a pigeon navigates by the Sun even in cloudy weather.
(Slide 10)
X-ray radiation - This is electromagnetic ionizing radiation, occupying the spectral region between gamma and ultraviolet radiation within wavelengths from 10 -12 - 1 0 -8 m (frequencies 3 * 10 16 - 3-10 20 Hz). X-ray radiation was discovered in 1895 by the German physicist W. K. Roentgen. The most common source of X-ray radiation is an X-ray tube, in which electrons accelerated by an electrical field bombard a metal anode. X-rays can be produced by bombarding a target with high-energy ions. Some radioactive isotopes and 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
Images of objects in X-ray radiation are obtained on special X-ray photographic film. X-ray radiation can be recorded using an ionization chamber, a scintillation counter, secondary electron or channel electron multipliers, and microchannel plates. Due to its high penetrating ability, X-ray radiation is used in X-ray diffraction analysis (studying the structure of a crystal lattice), in studying the structure of molecules, detecting defects in samples, in medicine (X-rays, fluorography, treatment of cancer), in flaw detection (detection of defects in castings, rails) , in art history (discovery of ancient painting hidden under a layer of later painting), in astronomy (when studying X-ray sources), and forensic science. A large dose of X-ray radiation leads to burns and changes in the structure of human blood. The creation of X-ray receivers and their placement on space stations made it possible to detect X-ray radiation from hundreds of stars, as well as the shells of supernovae and entire galaxies.
(Slide 11)
Gamma radiation - short-wave electromagnetic radiation, occupying the entire frequency range = 8∙10 14 - 10 17 Hz, which corresponds to wavelengths = 3.8·10 -7 - 3∙10 -9 m. Gamma radiation was discovered by the French scientist Paul Villard in 1900.
While studying radium radiation in a strong magnetic field, Villar discovered short-wave electromagnetic radiation that, like light, is not deflected by a magnetic field. It was called gamma radiation. Gamma radiation is associated with nuclear processes, radioactive decay phenomena 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 and in flaw detection. Gamma radiation has a negative effect on humans.
(Slide 12)
So, low frequency radiation, radio waves, infrared radiation, visible radiation, ultraviolet radiation, x-rays,-radiation are various types of electromagnetic radiation.
If you mentally arrange these types according to increasing frequency or decreasing wavelength, you will get a wide continuous spectrum - a scale of electromagnetic radiation (teacher shows scale). Dangerous types of radiation include: gamma radiation, x-rays and ultraviolet radiation, the rest are safe.
The division of electromagnetic radiation into ranges is conditional. There is no clear boundary between the regions. The names of the regions have developed historically; they only serve as a convenient means of classifying radiation sources.
(Slide 13)
All ranges of the electromagnetic radiation scale have common properties:
the physical nature of all radiation is the same
all radiation propagates in vacuum at the same speed, equal to 3 * 10 8 m/s
all radiations 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.
(Slide 14)
Conclusion:
The entire scale of electromagnetic waves is evidence that all radiation has both quantum and wave properties.
Quantum and wave properties in this case do not exclude, but complement each other.
Wave properties appear more clearly at low frequencies and less clearly at high frequencies. Conversely, quantum properties appear more clearly at high frequencies and less clearly at low frequencies.
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 confirmation of the law of dialectics (the transition of quantitative changes into qualitative ones).
Abstract (learn), fill in the table
last column (effect of EMR on humans) and
prepare a report on the use of EMR
Development content
GU LPR "LOUSOSH No. 18"
Lugansk
Karaseva I.D.
GENERALIZED RADIATION STUDY PLAN
1. Range name.
2. Wavelength
3. Frequency
4. Who was it discovered by?
5. Source
6. Receiver (indicator)
7. Application
8. Effect on humans
TABLE “ELECTROMAGNETIC WAVE SCALE”
Name of radiation
Wavelength
Frequency
Opened by
Source
Receiver
Application
Effect on humans
The radiations differ from each other:
- by method of receipt;
- by registration method.
Quantitative differences in wavelengths lead to significant qualitative differences; they are absorbed differently by matter (short-wave radiation - X-rays and gamma radiation) - are weakly absorbed.
Short-wave radiation reveals the properties of particles.
Low frequency vibrations
Wavelength (m)
10 13 - 10 5
Frequency Hz)
3 · 10 -3 - 3 · 10 5
Source
Rheostatic alternator, dynamo,
Hertz vibrator,
Generators in electrical networks (50 Hz)
Machine generators of high (industrial) frequency (200 Hz)
Telephone networks (5000Hz)
Sound generators (microphones, loudspeakers)
Receiver
Electrical devices and motors
History of discovery
Oliver Lodge (1893), Nikola Tesla (1983)
Application
Cinema, radio broadcasting (microphones, loudspeakers)
Radio waves
Wavelength(m)
Frequency Hz)
10 5 - 10 -3
Source
3 · 10 5 - 3 · 10 11
Oscillatory circuit
Macroscopic vibrators
Stars, galaxies, metagalaxies
Receiver
History of discovery
Sparks in the gap of the receiving vibrator (Hertz vibrator)
Glow of a gas discharge tube, coherer
B. Feddersen (1862), G. Hertz (1887), A.S. Popov, A.N. Lebedev
Application
Extra long- Radio navigation, radiotelegraph communication, transmission of weather reports
Long– Radiotelegraph and radiotelephone communications, radio broadcasting, radio navigation
Average- Radiotelegraphy and radiotelephone communications, radio broadcasting, radio navigation
Short- amateur radio communications
VHF- space radio communications
UHF- television, radar, radio relay communications, cellular telephone communications
SMV- radar, radio relay communications, celestial navigation, satellite television
MMV- radar
Infrared radiation
Wavelength(m)
2 · 10 -3 - 7,6∙10 -7
Frequency Hz)
3∙10 11 - 3,85∙10 14
Source
Any heated body: candle, stove, radiator, electric incandescent lamp
A person emits electromagnetic waves with a length of 9 · 10 -6 m
Receiver
Thermoelements, bolometers, photocells, photoresistors, photographic films
History of discovery
W. Herschel (1800), G. Rubens and E. Nichols (1896),
Application
In forensic science, photographing earthly objects in fog and darkness, binoculars and sights for shooting in the dark, heating the tissues of a living organism (in medicine), drying wood and painted car bodies, alarm systems for protecting premises, infrared telescope.
Visible radiation
Wavelength(m)
6,7∙10 -7 - 3,8 ∙10 -7
Frequency Hz)
4∙10 14 - 8 ∙10 14
Source
Sun, incandescent lamp, fire
Receiver
Eye, photographic plate, photocells, thermocouples
History of discovery
M. Melloni
Application
Vision
Biological life
Ultraviolet radiation
Wavelength(m)
3,8 ∙10 -7 - 3∙10 -9
Frequency Hz)
8 ∙ 10 14 - 3 · 10 16
Source
Contains sunlight
Gas discharge lamps with quartz tube
Emitted by all solids with a temperature greater than 1000 ° C, luminous (except mercury)
Receiver
Photocells,
Photomultipliers,
Luminescent substances
History of discovery
Johann Ritter, Layman
Application
Industrial electronics and automation,
Fluorescent lamps,
Textile production
Air sterilization
Medicine, cosmetology
X-ray radiation
Wavelength(m)
10 -12 - 10 -8
Frequency Hz)
3∙10 16 - 3 · 10 20
Source
Electron X-ray tube (voltage at the anode - up to 100 kV, cathode - filament, radiation - high-energy quanta)
Solar corona
Receiver
Camera roll,
The glow of some crystals
History of discovery
V. Roentgen, R. Milliken
Application
Diagnostics and treatment of diseases (in medicine), Flaw detection (control of internal structures, welds)
Gamma radiation
Wavelength(m)
3,8 · 10 -7 - 3∙10 -9
Frequency Hz)
8∙10 14 - 10 17
Energy(EV)
9,03 10 3 – 1, 24 10 16 Ev
Source
Radioactive atomic nuclei, nuclear reactions, processes of converting matter into radiation
Receiver
counters
History of discovery
Paul Villard (1900)
Application
Flaw detection
Process control
Research of nuclear processes
Therapy and diagnostics in medicine
GENERAL PROPERTIES OF ELECTROMAGNETIC RADIATIONS
physical nature
all radiation is the same
all radiations spread
in a vacuum at the same speed,
equal to the speed of light
all radiations are detected
general wave properties
polarization
reflection
refraction
diffraction
interference
- The entire scale of electromagnetic waves is evidence that all radiation has both quantum and wave properties.
- Quantum and wave properties in this case do not exclude, but complement each other.
- Wave properties appear more clearly at low frequencies and less clearly at high frequencies. Conversely, quantum properties appear more clearly at high frequencies and less clearly at low frequencies.
- The shorter the wavelength, the brighter the quantum properties appear, and the longer the wavelength, the brighter the wave properties appear.
- § 68 (read)
- fill in the last column of the table (effect of EMR on a person)
- prepare a report on the use of EMR
