Electromagnetic field Electromagnetic waves
9th grade
Michael Faraday 1791-1867 In 1831, he discovered the phenomenon of electromagnetic induction - the emergence of an electric current in a conductor when the magnetic flux changes through the conductor circuit.
What forces cause the charges in the coil to move? The magnetic field itself, penetrating the coil, cannot do this, because The magnetic field acts exclusively on moving charges, and the conductor with the electrons in it is motionless.
James Clerk Maxwell 1831-1879 The greatest scientific achievement in 1865 was the theory of the electromagnetic field he created, which he formulated in the form of a system of several equations expressing all the basic laws of electromagnetic phenomena.
Fundamental property of the field: Any change in the magnetic field over time gives rise to an alternating electric field, and any change in the electric field over time gives rise to an alternating magnetic field.
The source of a single electromagnetic field is accelerated electric charges
Mechanism of occurrence of induction current
The resulting vortex electric field, under the influence of which free charges, always present in the conductor, come into directed motion. The galvanometer plays the role of an indicator, detecting the electric field in space ( electricity).
The following conclusion follows from Maxwell's theory: A rapidly varying electromagnetic field propagates in space in the form of transverse waves.
James Maxwell based on theory:
- Waves propagate not only in matter, but also in vacuum. The speed of wave propagation in vacuum is 300,000 km/s.
- Waves propagate not only in matter, but also in vacuum.
- The speed of wave propagation in vacuum is 300,000 km/s.
- An electromagnetic wave is a system of electric and magnetic fields generating each other and propagating in space
Characteristics of the electric field - intensity ()
The electric field strength at any point is equal to the force ratio , with which the field acts on a point positive charge placed at that point, to the value of that charge q.
Characteristics of the magnetic field - magnetic induction vector (
For electromagnetic waves the same relationships between the wavelength and its speed are valid
With = 3 10 8 m/s, period T and frequency ν, as for mechanical waves. λ= = With T
Heinrich Rudolf Hertz 1857-1894 In 1888, he experimentally proved the existence of electromagnetic waves predicted by Maxwell. Established that the speed of propagation of electromagnetic waves is equal to the speed of light
- 1. Survey on the topic “Receiving alternating current»
- 3. Electromagnetic waves.
- 4. Consolidation.
- 5. Homework
Lesson Plan
Electromagnetic field. Faraday's experiments and Maxwell's hypothesis
Electric current occurs in the presence of an electric field.
And if you remove the conductor, will the field remain?
What field is this?
Electric, vortex.
James Clark Maxwell
Michael Faraday
Electromagnetic induction
- Any change in the magnetic field over time gives rise to an alternating electric field, and any change in the electric field over time gives rise to an alternating magnetic field.
Heinrich Rudolf Hertz
Proved experimentally the existence of E M V
Alexander Stepanovich Popov (1859-1906)
Used E M V for communication
ELECTROMAGNETIC WAVES are a system of variable electric and magnetic fields generating each other and propagating in space.
- this is an electromagnetic field propagating in space with a finite speed depending on the properties of the medium.
- The source of electromagnetic waves are accelerated moving electric charges.
Properties of electromagnetic waves
- - propagate not only in matter, but also in vacuum; - propagate in a vacuum at the speed of light
- (C = 300,000 km/s); - these are transverse waves; - these are traveling waves (transfer energy).
- All the space around us is permeated with electromagnetic radiation. The sun, the bodies around us, and transmitter antennas emit electromagnetic waves, which, depending on their oscillation frequency, carry different names.
- Radio waves are electromagnetic waves (with a wavelength from more than 10,000 m to 0.005 m), used to transmit signals (information) over a distance without wires.
ELECTROMAGNETIC WAVE SCALE
- In radio communications, radio waves are created by high-frequency currents flowing in an antenna. Radio waves of different wavelengths travel differently.
Radio waves
- Electromagnetic radiation with a wavelength less than 0.005 m but greater than 770 nm, i.e., lying between the radio wave range and the visible light range, is called infrared radiation (IR). Infrared radiation emit any heated bodies. Sources of infrared radiation are stoves, water heating radiators, and incandescent electric lamps. Using special devices, infrared radiation can be converted into visible light and images of heated objects can be obtained in complete darkness. Infrared radiation is used for drying painted products, building walls, and wood.
Infrared radiation
Light - visible radiation
- Visible light includes radiation with a wavelength of approximately 770 nm to 380 nm, from red to violet light. The significance of this part of the spectrum of electromagnetic radiation in human life is extremely large, since a person receives almost all information about the world around him through vision. The light is prerequisite for the development of green plants and therefore a necessary condition for the existence of life on Earth.
- Electromagnetic radiation with a wavelength shorter than that of violet light, invisible to the eye, is called ultraviolet radiation (UV). Ultraviolet radiation can kill pathogenic bacteria, so it is widely used in medicine. Ultraviolet radiation from sunlight causes biological processes, leading to darkening of human skin - tanning. Gas-discharge lamps are used as sources of ultraviolet radiation in medicine. The tubes of such lamps are made of quartz, transparent to ultraviolet rays; That's why these lamps are called quartz lamps.
X-rays (Ri)
- invisible to the eye. They pass without significant absorption through significant layers of matter that are opaque to visible light. X-rays are detected by their ability to cause a certain glow in certain crystals and act on photographic film. The ability of X-rays to penetrate thick layers of matter is used to diagnose diseases internal organs person.
- In technology, X-rays are used to control internal structure various products, welds. X-rays have strong biological effects and are used to treat certain diseases.
X-ray beam
DO YOU KNOW?
At discos they use ultraviolet lamps, under which the light material begins to glow. This radiation is relatively safe for animals and plants. UV lamps used for artificial tanning and in medicine require eye protection, because may cause temporary vision loss. UV - bactericidal lamps used to disinfect premises have a carcinogenic effect on the skin and burn plant leaves.
The human body is also a source of electric and magnetic fields. Each organ has its own electromagnetic fields. Throughout life, a person's field constantly changes. The most advanced device for determining human electromagnetic fields is an encephalograph. It allows you to accurately measure the field at different points around the head and, from this data, restore the distribution of electrical activity in the cerebral cortex. With the help of an encephalograph, doctors diagnose many diseases.
- EM waves are different from sound waves
- 1. No reflection of waves from the boundary of two media.
- 2. Diffusion in a vacuum.
- 3. Period.
- 4. Wavelength.
- In what case does an EM wave appear in space?
- 1 . A direct current flows through the conductor.
- 2. a charged particle moves in a straight line with variable speed.
- 3. A charged particle moves uniformly and rectilinearly.
- 4. The magnet lies on a steel stand.
Fixing the material
Who predicted the existence of electromagnetic waves?
1. H. Oersted
2. M. Faraday
3. J.C. Maxwell
- Arrange the series of waves in ascending frequency:
- 1. ultraviolet.
- 2. Infrared radiation
- 3. X-rays.
- 4. Visible light.
Fixing the material
Properties of lines of force: Properties of lines of force: Start on positive charges, Start on positive charges, end on negative; end in negative; The denser the lines of force are, the denser the lines of force are, the greater the tension. the greater the tension.
B N E Electromagnetic induction An alternating magnetic field creates an alternating electric field. The faster the magnetic field induction changes, the greater the electric field strength. An alternating electric field is called a vortex field, since its lines of force are closed like the induction lines of a magnetic field. 0
E B E E V V V The electromagnetic field is a combination of two inextricably related friend with each other, mutually generating changing fields: alternating electric and alternating magnetic fields. The source of the electromagnetic field is charges moving with acceleration.
Electromagnetic fields cell phones The most harmful is high-frequency radiation in the centimeter range. Facilities mobile communications They are still operating at the very beginning of this range, but the operating frequency is gradually increasing. The effect of electromagnetic fields on the human body manifests itself in a functional disorder of the central nervous system. Subjective sensations in this case include increased fatigue, drowsiness or, conversely, sleep disturbance, headaches, etc. With systematic irradiation, persistent neuropsychiatric diseases, changes in blood pressure, and slowing of the pulse are observed.
Safety advice: do not talk on mobile phone for a long time, and not at all for reasons tariff plan; Do not bring the phone to your head immediately after pressing the start dialing button, because at this moment, electromagnetic radiation is several times greater than during the conversation itself; Beware of staying near the provider’s repeater antenna for a long time, since it constantly emits a fairly powerful signal in all directions; When choosing a phone model, give preference to devices with external antennas and good sensitivity stated in the certificates.
Is electromagnetic radiation harmful to health? On this moment Science has not quantitatively proven a direct connection between the level of electromagnetic fields and cancer and other types of morbidity. However, qualitatively such a connection can be traced: in places where people are exposed to electromagnetic radiation, cancer and disorders of the cardiovascular and autonomic nervous systems are more often detected. The nervous system and visual organs are the most sensitive.
Artificial electromagnetic fields are harmful to everyone, but especially to high-risk groups: children, pregnant women, people with diseases of the central nervous, hormonal, cardiovascular systems, and allergy sufferers. It’s a good idea to install an air ionizer in your apartment - it reduces the impact of electrostatic fields. House flowers - begonias and violets - also saturate the air with very useful ions. A low-frequency electromagnetic field is formed around operating microwave ovens, which decreases to a safe level within a radius of at least 0.5 m. Televisions emit an electromagnetic field in all directions, even in standby mode. Therefore, it is better to unplug them at night.
Receiver elements: 1. Power source. Supplies energy to the circuit. 2. Antenna. Receives electromagnetic waves. 3. Grounding. Increases wave reception range. 4. Kogerer. Controls the current in the receiver circuit. 5. Call. Registers received electromagnetic waves. Provides automatic wave reception.
Improvement of the receiver On May 7, 1895, at a meeting of the Russian Physico-Chemical Society, A. S. Popov demonstrated the world’s first radio receiver. Ten months later, on March 24, 1896, A.S. Popov transmitted the world’s first radiogram of the two words “Heinrich Hertz” over a distance of 250 m. In the summer of the following year, the wireless communication range was increased to 5 km. In 1899, he designed a receiver for receiving signals by ear using a telephone receiver. In 1897 A.S. Popov received radio waves from thunderclouds. The reception range was 30 km. Lightning detector A.S. Popova
In 1900, A.S. Popov established communications in the Baltic Sea at a distance of over 45 km between the islands of Gogland and Kutsalo, near the city of Kotka. This world's first practical wireless communication line served the rescue expedition to remove the battleship Admiral General Apraksin, which had landed on the rocks off the southern coast of Gogland. The first radiogram transmitted by A.S. Popov to the island of Gogland on February 6, 1900, contained an order for the icebreaker Ermak to go to the aid of fishermen carried out to sea on an ice floe. The icebreaker complied with the order and 27 fishermen were rescued. The world's first practical line, which began its work by rescuing people swept out to sea, clearly proved the advantages of this type of communication. Battleship "Admiral General Apraksin". Behind is the icebreaker "Ermak".
In order to perpetuate the memory of A. S. Popov, a gold medal named after A. S. Popov was established, awarded annually for outstanding work and inventions in the field of radio. The Fatherland appreciated the services of the brilliant inventor and patriotic scientist to the Motherland. In 1945, the 50th anniversary of the invention of radio was widely celebrated in our country. The anniversary was celebrated on May 7, the day when A. S. Popov publicly demonstrated his invention for the first time. In this regard, the government established May 7 as Radio Day.
Propagation of radio waves Radiolocation Questions: 1. Definition of radio waves. 2.Types of radio waves. Wavelength range. 3. Due to what phenomena do radio waves propagate? Explain with a drawing. 4. Determination of radar. 5. What phenomenon is radar based on?
Slide 1
Electromagnetic field
These are alternating electric and magnetic fields that generate each other. The theory of the electromagnetic field was created by James Maxwell in 1865. He theoretically proved that: Any change in the magnetic field over time gives rise to a changing electric field, and any change in the electric field over time gives rise to a changing magnetic field. If electric charges move with acceleration, then the electric field they create periodically changes and itself creates an alternating magnetic field in space, etc.
Slide 2
Electromagnetic field sources can be
moving magnet; - an electric charge moving with acceleration or oscillating (in contrast to a charge moving at a constant speed, for example, in the case of direct current in a conductor, a constant magnetic field is created here).
Slide 3
Conditions for the existence of fields
The electric field always exists around the electric charge, in any reference system, the magnetic field - in the one relative to which electric charges move, the electromagnetic field - in the reference system relative to which electric charges move with acceleration.
Slide 4
TRY SOLVING!
A piece of amber was rubbed against a cloth, and it charged static electricity. What kind of field can be found around motionless amber? Around a moving one? A charged body is at rest relative to the surface of the earth. The car moves uniformly and rectilinearly relative to the surface of the earth. Is it possible to detect a constant magnetic field in the reference frame associated with a car? What field appears around an electron if it: is at rest; moves at a constant speed; moving with acceleration?
Slide 5
ELECTROMAGNETIC WAVES
This is an electromagnetic field propagating in space with a finite speed depending on the properties of the medium.
Slide 6
Properties of electromagnetic waves:
They spread not only in matter, but also in vacuum; - propagate in vacuum at the speed of light (C = 300,000 km/s); - these are transverse waves; - these are traveling waves (transfer energy). The source of electromagnetic waves are accelerated moving electric charges. Oscillations of electric charges are accompanied by electromagnetic radiation having a frequency equal to the frequency of charge oscillations.
Slide 7
ELECTROMAGNETIC WAVE SCALE
All the space around us is permeated with electromagnetic radiation. The sun, the bodies around us, and transmitter antennas emit electromagnetic waves, which, depending on their oscillation frequency, have different names. Meters
Slide 8
abstracts
1. Radio waves 2. Infrared radiation 3. Visible radiation 4. Ultraviolet radiation 5. X-rays 6. Gamma radiation
Slide 9
We solve problems
Determine the frequency of electromagnetic waves in the air, the length of which is 2 cm. What is the length of the waves sent by a radio station operating at a frequency of 1400 kHz. The radio transmitter operates at a frequency of 6 MHz. How many waves are there at a distance of 100 km in the direction of the radio signal? The current strength in the winding of the alternator changes according to the graph. Determine the amplitude, period, and frequency of current oscillations.
Slide 10
IT'S INTERESTING THAT...
Reinforced concrete houses shield external “street” electromagnetic fields, so inside such a house the influence of external fields is not felt. There are many electrical appliances used in our homes nowadays. All of them create electromagnetic fields during operation. Even a switched-on iron is surrounded by an electromagnetic field within a radius of approximately 25 cm; an electric kettle has an electromagnetic field that is twice as wide. The electromagnetic field of a regular electric razor is quite strong, so an electric razor is only good for short-term use. TV is a strong source of electromagnetic field (and color - in to a greater extent than black and white), but at a distance of 1.5 meters from it the electromagnetic background becomes safe. When using a working microwave oven, it is safe to be at a distance of 1-1.5 meters from it, although turning on the oven should also be quite short. The electromagnetic field of the computer is strongest from the back wall of the monitor, so it is more convenient to install it in the corner of the room. It is safe to sit at arm's length in front of the screen.
Lesson type: A lesson in mastering knowledge based on existing knowledge (with elements of generalization and systematization).
Lesson objectives:
educational: repeat and generalize students’ knowledge about electric and magnetic fields; introduce the concept of electromagnetic field; to form in students an idea of the electric and magnetic fields as a single whole - a single electromagnetic field.
- developing : activation of mental activity (by comparison); development of skills to compare, identify patterns, generalize, and think logically.
- educational : cultivate the ability to overcome difficulties, listen to opponents, defend your point of view, respect others.
Forms of organizing educational activities: frontal, individual.
Teaching methods: partial-search ( heuristic conversation), teaching programming (questions are asked), cluster method, the lesson is accompanied by an illustrative presentation
Means of education: projector, PC.
Types of control: final control based on the results of activity in the lesson.
Lesson Plan
1.Organization of the beginning of the lesson.
- Updating and summarizing knowledge
- Learning new material.
4. Consolidation of knowledge, skills and abilities. Cluster method
- Homework.
- Reflection and grading.
During the classes
I.Organization of the beginning of the lesson.
Slide 1 Lesson topic
Justification of the significance of the topic being studied We have been studying electrical and magnetic phenomena for quite a long time. The time has come to summarize all the information we have received, systematize it as much as possible and consider various electromagnetic phenomena from the point of view of their unity and generality.
Voicing goals and lesson plan
II. Updating and summarizing knowledge
Slide 2 The relationship between electricity and magnetism
How were magnetic and electric fields explained until the beginning of the 19th century? Was a relationship established between them or were they perceived as two completely independent phenomena?
Please remember what phenomena indicated the relationship between electricity and magnetism?
Which scientists contributed to the development of the theory of the relationship between electricity and magnetism?
Slide 3 Portrait of Oersted
Slide 4 Oersted's experience
Explain the essence of Oersted's experiment depicted in the figure?
What did Oersted manage to establish?
Slide 5 Portrait of Ampere
Slide 6 Ampere's law
What is shown in the picture? (action of a magnetic field on a current-carrying conductor)
What parameters determine the force acting on a current-carrying conductor placed in a magnetic field?
How to determine the direction of this force?
Formulate Ampere's law.
How will two current-carrying conductors interact? (Fig. 2 on slide)
Let's remember what hypothesis Ampere put forward to explain the magnetic properties of bodies?
Slide 7 Portrait of Faraday
Slide 8 Electromagnetic induction
What phenomenon was Faraday able to observe? What is the essence of the experiments he conducted? (explain based on the diagram shown on the slide)
What other way can one observe the appearance of an induced current? (Fig. 2 on slide)
What conclusion did Faraday draw from his experiments?
Let's formulate the essence of the phenomenon of electromagnetic induction.
Slide 9 Summarizing and summing up
What general conclusions can be drawn based on the three great discoveries of the 19th century? How are electricity and magnetism related?
So, by the middle of the 19th century. it was known:
- Electric current (moving charges) generates a magnetic field around itself.
- A constant magnetic field has an orienting effect on a current-carrying conductor (and moving charges, respectively)
- An alternating magnetic field is capable of generating an electric current (i.e., causing charged particles to move in a directed direction through an electric field)
And one Scot wondered (Use leading questions to try to bring students to the same idea):
if an alternating magnetic field generates an electric field, then isn’t there an inverse process in nature - Doesn't the electric field, in turn, generate a magnetic field??
III. Learning new material.(accompanied by leading questions, heuristic conversation)
Slide 10 Portrait of Maxwell
Slide 11 Maxwell's hypothesis
What can be assumed based on the above? What will happen when we have a changing magnetic field? (a hypothesis made by Maxwell)
Maxwell's Hypothesis: Whenever an electric field changes with time, it produces a magnetic field.
The hypothesis must be confirmed by experiment.
How can an alternating electric field be obtained?
Figure 1. Electric field of a capacitor.
When charging a capacitor, a changing electric field exists in the space between the plates .
Let's think about what a magnetic field generated by an alternating electric field might look like? (for this we can recall and draw an analogy with the magnetic field generated by a conductor with current)
Figure 2. A changing electric field generates a vortex magnetic field
A changing electric field creates the same magnetic field as if there were an electric current between the plates of a capacitor.
Slide 12 Direction of the magnetic induction vector B:
The lines of magnetic induction of the generated magnetic field cover the lines of electric field strength.
When the electric field strength increases, the direction of the magnetic induction vector forms a right screw with the direction of vector E. When it decreases, it forms a left screw ( explanatory drawing) .
When the magnetic field changes, the picture is similar ( explanatory drawing) .
What conclusion does this suggest?
Slide 13 Maxwell's derivation
Fields do not exist separately, independently of each other.
It is impossible to create an alternating magnetic field without simultaneously creating an electric field in space. And vice versa,
An alternating electric field does not exist without a magnetic field.
Electric and magnetic fields are a manifestation of a single whole - ELECTROMAGNETIC FIELD.
No less important is the fact that an electric field without a magnetic field, and vice versa, can only exist in relation to certain frames of reference.
Thus, a charge at rest creates only an electric field. But the charge is at rest only relative to a certain reference system, and relative to another it will move and, therefore, create a magnetic field.
Slide 14 Definition of electromagnetic field
Electromagnetic field– a special form of matter through which interaction between electrically charged particles occurs.
An electromagnetic field in a vacuum is characterized by the electric field strength vector E and magnetic induction B, which determine the forces acting from the field on stationary and moving charged particles.
Slide 15 Conclusion
In 1864 J. Maxwell creates electromagnetic field theory, according to which electric and magnetic fields exist as interconnected components of a single whole - the electromagnetic field.
This theory with single point of view explained the results of all previous studies in the field of electrodynamics
IV. Consolidation of knowledge, skills and abilities. Cluster method
Key phrase “Electromagnetic field”
V. Homework: § 17
VI. Reflection and grading.
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