"Electromagnetic waves".
Lesson objectives:
Educational:
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 one?
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.
Summarizing.
Literature.
Scenario for conducting a lesson using modern pedagogical technologies.
Lesson topic
"Electromagnetic waves"
Lesson objectives:
Educational : Study electromagnetic waves, the history of their discovery, characteristics and properties.
Developmental : develop the ability to observe, compare, analyze
Educating : formation of scientific and practical interest and worldview
Lesson plan:
Repetition
Introduction to the history of the discovery of electromagnetic waves:
Faraday's law (experiment)
Maxwell's hypothesis (experiment)
Graphical and mathematical representation of an electromagnetic wave
Electromagnetic wave graph
Electromagnetic Wave Equations
Characteristics of an electromagnetic wave: propagation speed, frequency, period, amplitude
Experimental confirmation of the existence of electromagnetic waves.
Closed oscillatory circuit
Open oscillatory circuit. Hertz's experiments
Properties of electromagnetic waves
Updating knowledge
Getting homework
Equipment:
Computer
interactive board
Projector
Inductor
Galvanometer
Magnet
Hardware-software digital measuring complexlaboratory equipment "Scientific entertainment"
Personal ready-made cards with a graphical representation of an electromagnetic wave, basic formulas and homework (Appendix 1)
Video material from the electronic supplement to the Physics kit, grade 11 ( UMK Myakishev G. Ya., Bukhovtsev B.B.)
TEACHER ACTIVITIES
Information card
STUDENT ACTIVITY
Motivational stage – Introduction to the lesson topic
Dear Guys! Today we will begin to study the last section in the large topic “Oscillations and Waves” regarding electromagnetic waves.
We will learn the history of their discovery and meet the scientists who had a hand in it. Let's find out how we were able to obtain an electromagnetic wave for the first time. Let's study the equations, graphs and properties of electromagnetic waves.
First, let's remember what a wave is and what types of waves do you know?
A wave is an oscillation that propagates over time. Waves are mechanical and electromagnetic.
Mechanical waves are diverse, they propagate in solid, liquid, gaseous media, can we detect them with our senses? Give examples.
Yes, in solid media this can be earthquakes, vibrations of the strings of musical instruments. In liquids there are waves on the sea, in gases they are the propagation of sounds.
With electromagnetic waves, things are not so simple. You and I are in a classroom and do not feel or realize at all how many electromagnetic waves permeate our space. Maybe some of you can already give examples of the waves that are present here?
Radio waves
TV waves
- Wi- Fi
Light
Radiation from mobile phones and office equipment
Electromagnetic radiation includes radio waves and light from the Sun, X-rays and radiation, and much more. If we visualized them, we would not be able to see each other behind such a huge number of electromagnetic waves. They serve as the main carrier of information in modern life and at the same time are a powerful negative factor affecting our health.
Organization of student activities to create a definition of an electromagnetic wave
Today we will follow in the footsteps of the great physicists who discovered and generated electromagnetic waves, find out what equations describe them, and explore their properties and characteristics. We write down the topic of the lesson “Electromagnetic waves”
You and I know that in 1831. English physicist Michael Faraday experimentally discovered the phenomenon of electromagnetic induction. How does it manifest itself?
Let's repeat one of his experiments. What is the formula of the law?
Students perform Faraday's experiment
A time-varying magnetic field leads to the appearance of induced emf and induced current in a closed circuit.
Yes, an induced current appears in a closed circuit, which we register using a galvanometer
Thus, Faraday experimentally showed that there is a direct dynamic relationship between magnetism and electricity. At the same time, Faraday, who had not received a systematic education and had little knowledge of mathematical methods, could not confirm his experiments with theory and mathematical apparatus. Another outstanding English physicist James Maxwell (1831-1879) helped him in this.
Maxwell gave a slightly different interpretation to the law of electromagnetic induction: “Any change in the magnetic field generates a vortex electric field in the surrounding space, the lines of force of which are closed.”
So, even if the conductor is not closed, a change in the magnetic field causes an inductive electric field in the surrounding space, which is a vortex field. What are the properties of a vortex field?
Properties of the vortex field:
His lines of tension are closed
Has no sources
It should also be added that the work done by the field forces to move a test charge along a closed path is not zero, but the induced emf
In addition, Maxwell hypothesizes the existence of an inverse process. Which one do you think?
“A time-varying electric field generates a magnetic field in the surrounding space”
How can we get a time-varying electric field?
Time-varying current
What is current?
Current - orderedly moving charged particles, in metals - electrons
Then how should they move for the current to be alternating?
With acceleration
That's right, it is the accelerated moving charges that cause an alternating electric field. Now let's try to record a change in the magnetic field using a digital sensor, bringing it to wires with alternating current
A student conducts an experiment to observe changes in the magnetic field
On the computer screen we observe that when the sensor is brought to a source of alternating currents and fixed, a continuous oscillation of the magnetic field occurs, which means an alternating electric field appears perpendicular to it
Thus, a continuous interconnected sequence arises: a changing electric field generates an alternating magnetic field, which, by its appearance, again generates a changing electric field, etc.
Once the process of changing the electromagnetic field has begun at a certain point, it will then continuously capture more and more new areas of the surrounding space. The propagating alternating electromagnetic field is an electromagnetic wave.
So, Maxwell’s hypothesis was only a theoretical assumption that did not have experimental confirmation, but on its basis he was able to derive a system of equations describing the mutual transformations of magnetic and electric fields and even determine some of their properties.
The children are given personal cards with graphs and formulas.
Maxwell's calculations:
Organization of student activities to determine the speed of electromagnetic waves and other characteristics
ξ-dielectric constant of the substance, we considered the capacitance of the capacitor,- magnetic permeability of a substance – we characterize the magnetic properties of substances, shows whether the substance is paramagnetic, diamagnetic or ferromagnetic
Let's calculate the speed of an electromagnetic wave in a vacuum, then ξ = =1
The guys are calculating the speed , after which we check everything on the projector
The length, frequency, cyclic frequency and period of wave oscillations are calculated using formulas familiar to us from mechanics and electrodynamics, please remind me of them.
The guys write down the formulas λ=υT on the board, , , check their correctness on the slide
Maxwell also theoretically derived a formula for the energy of an electromagnetic wave, and . W Em ~ 4 This means that in order to detect a wave more easily, it must be of high frequency.
Maxwell's theory caused a resonance in the physical community, but he did not have time to experimentally confirm his theory, then the baton was picked up by the German physicist Heinrich Hertz (1857-1894). Surprisingly, Hertz wanted to refute Maxwell’s theory, for this he came up with a simple and ingenious solution for producing electromagnetic waves.
Let's remember where we have already observed the mutual transformation of electric and magnetic energies?
In an oscillatory circuit.
IN closed oscillatory circuit, what does it consist of?
This is a circuit consisting of a capacitor and a coil in which mutual electromagnetic oscillations occur
That’s right, only the oscillations occurred “inside” the circuit, and the main task of scientists was to generate these oscillations into space and, naturally, to register them.
We have already said thatwave energy is directly proportional to the fourth power of frequency . W Em~ν 4 . This means that in order to detect a wave more easily, it must be of high frequency. What formula determines the frequency in an oscillatory circuit?
Closed loop frequency
What can we do to increase the frequency?
Reduce capacitance and inductance, which means reducing the number of turns in the coil and increasing the distance between the capacitor plates.
Then Hertz gradually “straightened” the oscillatory circuit, turning it into a rod, which he called a “vibrator”.
The vibrator consisted of two conductive spheres with a diameter of 10-30 cm, mounted on the ends of a wire rod cut in the middle. The ends of the rod halves at the cut site ended in small polished balls, forming a spark gap of several millimeters.
The spheres were connected to the secondary winding of the Ruhmkorff coil, which was a source of high voltage.
The Ruhmkorff inductor created a very high voltage, on the order of tens of kilovolts, at the ends of its secondary winding, charging the spheres with charges of opposite signs. At a certain moment, the voltage between the balls was greater than the breakdown voltage and aelectric spark , electromagnetic waves were emitted.
Let's remember the phenomenon of a thunderstorm. Lightning is the same spark. How does lightning appear?
Drawing on the board:
If a large potential difference occurs between the ground and the sky, the circuit “closes” - lightning occurs, current is conducted through the air, despite the fact that it is a dielectric, and the voltage is removed.
Thus, Hertz managed to generate an uh wave. But it still needs to be registered; for this purpose, as a detector or receiver, Hertz used a ring (sometimes a rectangle) with a gap - a spark gap, which could be adjusted. The alternating electromagnetic field excited an alternating current in the detector; if the frequencies of the vibrator and receiver coincided, resonance occurred and a spark also appeared in the receiver, which could be visually detected.
Hertz proved with his experiments:
1) the existence of electromagnetic waves;
2) waves are well reflected from conductors;
3) determined the speed of waves in air (it is approximately equal to the speed in vacuum).
Let's conduct an experiment on the reflection of electromagnetic waves
An experiment on the reflection of electromagnetic waves is shown: the student’s phone is put into a completely metallic vessel and friends try to call him.
The signal does not pass through
The guys answer the question from experience, why there is no cellular signal.
Now let's watch a video on the properties of electromagnetic waves and record them.
Reflection of e-waves: waves are well reflected from a metal sheet, and the angle of incidence is equal to the angle of reflection
Wave absorption: um waves are partially absorbed when passing through a dielectric
Wave refraction: um waves change their direction when moving from air to dielectric
Wave interference: the addition of waves from coherent sources (we will study in more detail in optics)
Wave diffraction - bending of obstacles by waves
The video fragment “Properties of electromagnetic waves” is shown
Today we learned the history of electromagnetic waves from theory to experiment. So, answer the questions:
Who discovered the law about the appearance of an electric field when a magnetic field changes?
What was Maxwell's hypothesis about the generation of a changing magnetic field?
What is an electromagnetic wave?
What vectors is it built on?
What happens to the wavelength if the vibration frequency of charged particles is doubled?
What properties of electromagnetic waves do you remember?
Guys' answers:
Faraday experimentally discovered the law of emf and Maxwell expanded this concept in theory
A time-varying electric field generates a magnetic field in the surrounding space
Spreading in spaceelectromagnetic field
Tension, magnetic induction, speed
Will decrease by 2 times
Reflection, refraction, interference, diffraction, absorption
Electromagnetic waves have different uses depending on their frequency or wavelength. They bring benefits and harm to humanity, so for the next lesson, prepare messages or presentations on the following topics:
How do I use electromagnetic waves
Electromagnetic radiation in space
Sources of electromagnetic radiation in my home, their impact on health
The impact of electromagnetic radiation from a cell phone on human physiology
Electromagnetic weapons
And also solve the following problems for the next lesson:
i =0.5 cos 4*10 5 π t
Tasks on cards.
Thank you for your attention!
Annex 1
Electromagnetic wave:
1,25664*10 -6 H/m – magnetic constant
Tasks:
The broadcast frequency of the Mayak radio station in the Moscow region is 67.22 MHz. What wavelength does this radio station operate on?
The current strength in an open oscillatory circuit varies according to the lawi =0.5 cos 4*10 5 π t . Find the wavelength of the emitted wave.
LESSON PLAN
on this topic " Electromagnetic field and electromagnetic waves"
| Full name | Kosintseva Zinaida Andreevna |
|
| Place of work | DF GBPOU "KTK" |
|
| Job title | teacher |
|
| Item | ||
| 5. | Class | 2nd year profession “Cook, confectioner”, “Welder” |
| 6. 7. | Subject Lesson number in topic | Electromagnetic field and electromagnetic waves. 27 |
| 8. | Basic tutorial | V.F. Dmitrieva Physics: for professions and technical specialties: for general education. institutions: textbook beginning. and secondary vocational education Textbook: -6th ed. ster.-M.: Publishing center "Academy", 2013.-448 p. |
Lesson objectives:
- educational
repeat and summarize students’ knowledge in the “Electrodynamics” section;
- developing
promote the development of the ability to analyze, put forward hypotheses, assumptions, make forecasts, observe and experiment;
development of the ability for self-esteem and introspection of one’s own mental activity and its results;
check the level of independent thinking of students in applying existing knowledge in various situations.
- educational
encouraging cognitive interest in the subject and surrounding phenomena;
nurturing the spirit of competition, responsibility for comrades, collectivism.
Lesson type Lesson - seminar
Forms of student work verbal transmission of information and auditory perception of information; visual transmission of information and visual perception of information; transfer of information through practical activities; stimulation and motivation; methods of control and self-control.
Facilities teach I : Presentations; reports; Crosswords; tasks for the tested survey;
Equipment: PC, ID, projector, presentationsppt, video lesson, PC-student workstations, tests.
Lesson structure and flow
Table 1.
STRUCTURE AND PROGRESS OF THE LESSON
| Lesson stage | Name of EORs used (indicating the serial number from Table 2) | Teacher activities (indicating actions with ESM, for example, demonstration) | Student activity | Time (per minute) |
|
| Organizing time | Greetings to students | Greet the teacher | |||
| Updating and correcting basic knowledge | 1. Oginsky “Polonaise” | Shows a video clip. | |||
| Introductory speech by the teacher | 1,. Presentation, Slide No. 1 Slide No. 2 | Announcing the topic of the lesson Declaration of goals and objectives | Listen and record | ||
| Repetition | Oral work with definitions and laws Test survey – Test No. 20 | Distributes among workplaces Includes electronic test log Shows the test on the screen | Work on a PC and in notebooks | ||
| Experiencing new discoveries Student performances 1. The brilliant self-taught Michael Faraday. 2. Founder of the electromagnetic field theory James Maxwell. 3. The great experimenter Heinrich Hertz. 4. Alexander Popov. Radio history 5. Watching a video about A.S. Popov | 1, Presentation, Slide No. 4 2. Presentation 3. Presentation 4. Presentation 5. Presentation | Coordinates student performance, assists and evaluates | Listen to students' speeches, take notes, ask questions, Characterize the performance | ||
| Reflection | 6, Crossword | Organizes work on a PC | Solving a crossword puzzle | ||
| Summing up the lesson | 1, Slide No. 10 | Gives grades and sums up | Give ratings | ||
| Homework | 1, Slide No. 5 | Explains homework - Presentation "" | Write down the task |
Appendix to the lesson plan
on the topic "Electromagnetic field and electromagnetic waves"
Table 2.
LIST OF EOR USED IN THIS LESSON
| Resource name | Type, type of resource | Information submission form (illustration, presentation, video clips, test, model, etc.) | ||
| Oginsky "Polonaise" | informational | video clip |
|
|
| Lesson summary | informational | presentation | ||
| Report “The brilliant self-taught Michael Faraday” | informational | presentation | ||
| Report " Founder of electromagnetic field theory James Maxwell» | informational | presentation | ||
| The great experimenter Heinrich Hertz" | informational | presentation | ||
| "Alexander Popov. Radio history" | informational | Presentation Video lesson The principle of radiotelephone communication. The simplest radio receiver. | Lkvideouroki.net. No. 20. |
|
| Film "A.S.Popov" | informational | Internet technology | www.youtube.com The invention of radio, Popov Alexander Stepanovich, Popov. |
|
| Practical | MyTest program. | No. 20 Lkvideouroki.net. |
||
| Crossword | Practical | presentation |
Physics teacher, Secondary School No. 42, Belgorod
Kokorina Alexandra Vladimirovna
Class: 9
Item: Physics.
the date of the:
Subject:“Electromagnetic field (EMF).”
Type: combined lesson .
Lesson objectives:
educational:
- trust previously acquired knowledge;
- ensure perception, comprehension, primary memorization of the concept of “electromagnetic field”, the relationship of electric and magnetic fields;
— organize students’ activities to reproduce learned information;
educational:
— education of labor motives and a conscientious attitude to work;
- nurturing motives for learning, a positive attitude towards knowledge;
— showing the role of physical experiment and physical theory in the study of physical phenomena.
developing:
— development of skills to creatively approach solving a wide variety of problems;
— development of skills to act independently;
Means of education:
- board and chalk;
Teaching methods:
- explanatory - illustrative .
Lesson structure (stages):
organizational moment (2 min);
updating basic knowledge (10 min);
learning new material (17 min);
checking understanding of the information received (8 min);
summing up the lesson (2 min);
information about homework (1 min).
During the classes
Student activities | ||||||||||||
- greetings "Hello guys". — recording of absentees"Who is absent today?" | - greet the teacher "Hello" - the duty officer calls those who are absent |
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- physical dictation “You have blank sheets of paper on your tables, sign them and indicate the number of the option you are sitting on. I will dictate questions to you one at a time, first for the 1st option, then for the 2nd option. Be careful " Questions for the dictation: 1.1 What generates a magnetic field? 1.2 How can you clearly show a magnetic field? 2.1 What is the nature of the NMP lines? 2.2 What is the nature of the WMD lines? 3.1 Magnetic induction: formula, units of measurement. 3.2 Magnetic induction lines are... 4.1 What can be determined by the right hand rule? 4.2 What can be determined by the left-hand rule? 5.1 The EMR phenomenon is... 5.2 Alternating current is... “Now pass your work to the first desks. Who failed the task?”(discuss the questions that caused difficulties) | - sign the work - answer questions Answers: 1.1 moving charges 1.2 magnetic lines 2.1 are curved, their density changes 2.2 parallel to each other, located at the same frequency 3.1 B = F/(I l), T 3.2 lines, tangents to which at each point of the field coincide with the direction of the magnetic induction vector 5.1 when the mp passing through the circuit of a closed conductor changes, a current arises in the conductor 5.2 current periodically varying in magnitude and direction over time |
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- conversation with the class: “The topic of our lesson is written on the board. And who can tell me in what year and by whom the EMP phenomenon was discovered?” “What is it?” “Under what conditions does current flow in a conductor?” “This means we can conclude that an alternating magnetic field penetrating a closed circuit of a conductor creates an electric field in it, under the influence of which an induced current arises.” — explanation of new material: “Based on this conclusion, James Clerk Maxwell in 1865 created a complex theory of EMF. We will consider only its main provisions. Write it down.” Basic provisions of the theory: 3. These variables generating each other e.p. and m.p. form EMF. 5. (next lesson) “A constant m.p. is created around charges moving at a constant speed. But if the charges move with acceleration, then the m.p. excited by them. changes periodically. Variable e.p. creates a variable m.p. in space, which in turn generates a variable e.p. etc." Variable e.p. – vortex. | - answer the teacher’s questions orally “Michael Faraday, in 1831" “when the mp passing through the contour of a closed conductor changes, a current arises in the conductor” “ if it contains e.p.” - write down in a notebook what the teacher dictates |
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“Now draw a table in your notebooks as on the board. Let’s fill it out together.”
| - draw a table and fill it out together with the teacher |
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- generalization and systematization: “So, what important concept did you learn about in class today? That's right, with the concept of EMF. What can you say about him?” - reflection: “who has difficulty understanding the material?” Assessing the behavior and performance of individual students in the classroom. | - answer questions |
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- information about homework Ҥ 51 , prepare for the test. The lesson is over. Goodbye". | - write down homework - say goodbye to the teacher: "Goodbye". |
Students should have in their notebooks:
Topic: “Electromagnetic field (EMF).”
1856 - J.C. Maxwell created the theory of EMF.
Basic provisions of the theory:
1. Any change over time m.p. leads to the appearance of a variable e.p.
2. Any change over time e.p. leads to the appearance of a variable m.p.
3. These variables generating each other e.p. and m.p. form EMF.
4. Source of EMF – accelerated moving charges.
Variable e.p. – vortex.
vortex | electrostatic | |
character | changes periodically over time | does not change over time |
source | accelerated charges | stationary charges |
power lines | closed | start with “+”; end with “-” |
Class: 11
Lesson objectives:
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
Org. Moment.
Annex 1. (SLIDE No. 1). 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)
(SLIDE No. 2)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.
(SLIDE No. 3)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) (SLIDE No. 4) 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.
(SLIDE No. 4). 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)
(SLIDE No. 5)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: ~ magnetic field creates ~ electric current
(SLIDE No. 6) 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)
(SLIDE No. 7). 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
(SLIDE No. 8) 250 m, then 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. (Slide No. 9). 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 one?
Consolidation.
Answer the questions:
(SLIDE No. 10)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.
(SLIDE No. 11)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)
Let's solve the problem.
The Kemerovo television center transmits two carrier waves: an image carrier wave with a radiation frequency of 93.4 kHz and a sound carrier wave with a frequency of 94.4 kHz. Determine the wavelengths corresponding to these radiation frequencies.
(SLIDE No. 12)Homework.
(SLIDE No. 13) 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.
Summarizing.
(SLIDE No. 14) Thank you for your attention and for your work!!!
Literature.
