Presentation on the topic: Electromagnetic oscillations. History of the discovery of electromagnetic waves Presentation on the topic of low-frequency radiation

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Electromagnetic wave scale. Types, properties and applications.

From the history of discoveries... 1831 - Michael Faraday established that any change in the magnetic field causes the appearance of an inductive (vortex) electric field in the surrounding space.

1864 – James Clerk Maxwell hypothesized the existence of electromagnetic waves capable of propagating in vacuum and dielectrics. Once started at some point, the process of change electromagnetic field will continuously capture new areas of space. This is an electromagnetic wave.

1887 - Heinrich Hertz published the work “On Very Fast Electric Oscillations,” where he described his experimental setup - a vibrator and a resonator - and his experiments. When electrical vibrations occur in the vibrator, a vortex alternating electromagnetic field appears in the space around it, which is recorded by the resonator.

Electromagnetic waves are electromagnetic oscillations propagating in space with a finite speed.

The entire scale of electromagnetic waves is evidence that all radiation has both quantum and wave properties. Wave properties appear more clearly at low frequencies and less clearly at high frequencies. And vice versa, 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.

Low-frequency oscillations Wavelength (m) 10 13 - 10 5 Frequency (Hz) 3 10 -3 - 3 10 3 Energy (EV) 1 – 1.24 10 -10 Source Rheostatic alternator, dynamo, Hertz vibrator, Generators in electrical networks (50 Hz) Machine generators of high (industrial) frequency (200 Hz) Telephone networks (5000 Hz) Sound generators (microphones, loudspeakers) Receiver Electrical devices and engines Discovery history Lodge (1893), Tesla (1983) Application Cinema, radio broadcasting (microphones, loudspeakers)

Radio waves are produced using oscillatory circuits and macroscopic vibrators. Properties: radio waves of different frequencies and with different wavelengths are absorbed and reflected differently by media. exhibit diffraction and interference properties. Wavelengths cover the region from 1 micron to 50 km

Application: Radio communications, television, radar.

Infrared radiation (thermal) Emitted by atoms or molecules of a substance. Infrared radiation is emitted by all bodies at any temperature. Properties: passes through some opaque bodies, as well as through rain, haze, snow, fog; produces chemical action(photographs); being absorbed by a substance, it heats it up; invisible; capable of interference and diffraction phenomena; recorded by thermal methods.

Application: Night vision device, forensics, physiotherapy, in industry for drying products, wood, fruits

Visible radiation Properties: reflection, refraction, affects the eye, capable of dispersion, interference, diffraction. Part electromagnetic radiation, perceived by the eye (from red to violet). The wavelength range occupies a small interval from approximately 390 to 750 nm.

Ultraviolet radiation Sources: gas-discharge lamps with quartz tubes. Radiated by everyone solids, for which t 0> 1 000 ° C, as well as luminous mercury vapor. Properties: High chemical activity, invisible, high penetrating ability, kills microorganisms, in small doses has a beneficial effect on the human body (tanning), but in large doses it has a negative effect, changes cell development, metabolism.

Application: in medicine, in industry.

X-rays are emitted at high electron accelerations. Properties: interference, X-ray diffraction by crystal lattice, high penetrating power. Irradiation in large doses causes radiation sickness. Obtained using an X-ray tube: electrons in a vacuum tube (p = 3 atm) are accelerated by an electric field at high voltage, reaching the anode, and are sharply decelerated upon impact. When braking, electrons move with acceleration and emit electromagnetic waves with a short length (from 100 to 0.01 nm)

Application: In medicine for the purpose of diagnosing diseases internal organs; in industry to control the internal structure of various products.

γ-radiation Sources: atomic nucleus (nuclear reactions). Properties: Has enormous penetrating power and has a strong biological effect. Wavelength less than 0.01 nm. Highest energy radiation

Application: In medicine, production (γ-flaw detection).

Impact of electromagnetic waves on the human body

Thank you for your attention!

“Electromagnetic oscillations” - Magnetic field energy. Option 1. Organizational stage. The reciprocal of capacitance, Radian (rad). Radian per second (rad/s). Option2. Fill out the table. The stage of generalization and systematization of the material. Lesson plan. Option 1 1.Which of the systems shown in the figure is not oscillatory? 3. Using the graph, determine a) the amplitude, b) the period, c) the frequency of oscillations. a) A. 0.2m B.-0.4m C.0.4m b) A. 0.4s B. 0.2s C.0.6s c) A. 5Hz B.25Hz C. 1.6Hz.

“Mechanical vibrations” - Wavelength (?) – the distance between nearby particles oscillating in the same phase. Harmonic vibration graph. Examples of free mechanical vibrations: Spring pendulum. Elastic waves are mechanical disturbances propagating in an elastic medium. Mathematical pendulum. Oscillations. Harmonic vibrations.

“Mechanical vibrations, grade 11” - There are waves: 2. Longitudinal - in which vibrations occur along the direction of propagation of the waves. Wave quantities: Visual representation of a sound wave. In a vacuum, a mechanical wave cannot arise. 1. Presence of an elastic medium 2. Presence of a source of vibrations - deformation of the medium.

“Small oscillations” - Wave processes. Sound vibrations. During the oscillation process, a transformation occurs kinetic energy to potential and back. Mathematical pendulum. Spring pendulum. The position of the system is determined by the deflection angle. Small fluctuations. The phenomenon of resonance. Harmonic vibrations. Mechanics. Equation of motion: m?l2???=-m?g?l?? or??+(g/l)??=0 Frequency and period of oscillation:

“Oscillatory systems” - External forces are forces acting on the bodies of the system from bodies not included in it. Oscillations are movements that are repeated at certain intervals. The friction in the system should be quite low. Conditions for the occurrence of free vibration. Forced vibrations are called vibrations of bodies under the influence of external periodically changing forces.

“Harmonic oscillations” - Figure 3. Ox – reference straight line. 2.1 Methods of representing harmonic vibrations. Such oscillations are called linearly polarized. Modulated. 2. The phase difference is equal to an odd number?, that is. 3. The initial phase difference is?/2. 1. The initial phases of oscillations are the same. The initial phase is determined from the relation.

“Waves in the Ocean” - The devastating consequences of the Tsunami. Movement earth's crust. Learning new material. Find out objects on contour map. Tsunami. The length in the ocean is up to 200 km, and the height is 1 m. The height of the Tsunami off the coast is up to 40 m. Strait. V. Bay. Wind waves. Ebbs and flows. Wind. Consolidation of the studied material. average speed Tsunami 700 – 800 km/h.

"Waves" - "Waves in the ocean." They spread at a speed of 700-800 km/h. Guess which extraterrestrial object causes the tides to rise and fall? The highest tides in our country are at Penzhinskaya Bay in the Sea of ​​Okhotsk. Ebbs and flows. Long gentle waves, without foamy crests, occurring in calm weather. Wind waves.

"Seismic waves" - Complete destruction. Felt by almost everyone; many sleepers wake up. Geographical distribution of earthquakes. Registration of earthquakes. On the surface of alluvium, subsidence basins are formed and filled with water. The water level in wells changes. On earth's surface waves are visible. There is no generally accepted explanation for such phenomena yet.

“Waves in a medium” - The same applies to a gaseous medium. The process of propagation of vibrations in a medium is called a wave. Consequently, the medium must have inert and elastic properties. Waves on the surface of a liquid have both transverse and longitudinal components. Consequently, transverse waves cannot exist in liquid or gaseous media.

“Sound waves” - The process of propagation of sound waves. Timbre is a subjective characteristic of perception, generally reflecting the characteristics of sound. Sound characteristics. Tone. Piano. Volume. Loudness - the level of energy in sound - is measured in decibels. Sound wave. As a rule, additional tones (overtones) are superimposed on the main tone.

“Mechanical waves, grade 9” - 3. By nature, waves are: A. Mechanical or electromagnetic. Plane wave. Explain the situation: There are not enough words to describe everything, The whole city is distorted. In calm weather, we are nowhere to be found, and when the wind blows, we run on the water. Nature. What "moves" in the wave? Wave parameters. B. Flat or spherical. The source oscillates along the OY axis perpendicular to OX.

The discovery of electromagnetic waves is a remarkable example of the interaction between experiment and theory. It shows how physics has united seemingly completely disparate properties - electricity and magnetism - by discovering in them different aspects of the same physical phenomenon - electromagnetic interaction. Today it is one of the four known fundamental physical interactions, which also include strong and weak nuclear interactions and gravity. A theory of electroweak interaction has already been constructed, which common positions describes electromagnetic and weak nuclear forces. There is also the next unifying theory - quantum chromodynamics - which covers the electroweak and strong interactions, but its accuracy is somewhat lower. Describe All Fundamental interactions from a unified position have not yet been achieved, although intensive research is being carried out in this direction within the framework of such areas of physics as string theory and quantum gravity.

Electromagnetic waves were predicted theoretically by the great English physicist James Clerk Maxwell (probably first in 1862 in On Physical Lines of Force, although detailed description theory was published in 1867). He diligently and with great respect tried to translate into strict mathematical language Michael Faraday's somewhat naive pictures describing electrical and magnetic phenomena, as well as the results of other scientists. Having ordered all electrical and magnetic phenomena in the same way, Maxwell discovered a number of contradictions and a lack of symmetry. According to Faraday's law, alternating magnetic fields generate electric fields. But it was not known whether alternating electric fields generate magnetic fields. Maxwell managed to get rid of the contradiction and restore the symmetry of the electric and magnetic fields by introducing an additional term into the equations, which described the appearance of a magnetic field when the electric field changes. By that time, thanks to Oersted's experiments, it was already known that D.C. creates a constant magnetic field around the conductor. The new term described a different source of the magnetic field, but it could be thought of as some kind of imaginary electric current, which Maxwell called displacement current, to distinguish it from ordinary current in conductors and electrolytes - conduction current. As a result, it turned out that alternating magnetic fields generate electric fields, and alternating electric fields generate magnetic ones. And then Maxwell realized that in such a combination the oscillating electric and magnetic field can break away from the conductors that generate them and move through the vacuum at a certain, but very high speed. He calculated this speed, and it turned out to be about three hundred thousand kilometers per second.

Shocked by the result, Maxwell wrote to William Thomson (Lord Kelvin, who, in particular, introduced the absolute temperature scale): “The speed of transverse wave oscillations in our hypothetical medium, calculated from the electromagnetic experiments of Kohlrausch and Weber, coincides so exactly with the speed of light calculated from Fizeau's optical experiments, that we can hardly refuse the conclusion that light consists of transverse vibrations of the same medium that causes electrical and magnetic phenomena" And further in the letter: “I received my equations while living in the provinces and not suspecting the proximity of the propagation speed I found magnetic effects to the speed of light, so I think that I have every reason to consider the magnetic and luminiferous mediums as one and the same medium...”

Maxwell's equations go far beyond the scope of a school physics course, but they are so beautiful and laconic that they should be placed in a prominent place in a physics classroom, because most natural phenomena that are significant to humans can be described with just a few lines of these equations. This is how information is compressed when previously heterogeneous facts are combined. Here is one type of Maxwell's equations in differential representation. Admire it.

I would like to emphasize that Maxwell’s calculations yielded a discouraging consequence: the oscillations of the electric and magnetic fields are transverse (which he himself emphasized all the time). And transverse vibrations propagate only in solids, but not in liquids and gases. By that time, it was reliably measured that the speed of transverse vibrations in solids (simply the speed of sound) is higher, the harder, roughly speaking, the medium (the higher the Young’s modulus and the lower the density) and can reach several kilometers per second. The speed of the transverse electromagnetic wave was almost one hundred thousand times higher than the speed of sound in solids. And it should be noted that the stiffness characteristic is included in the equation for the speed of sound in a solid body under the root. It turned out that the medium through which electromagnetic waves (and light) travel has monstrous elasticity characteristics. An extremely difficult question arose: “How do other bodies move through such a solid medium and not feel it?” The hypothetical medium was called ether, attributing to it both strange and, generally speaking, mutually exclusive properties - enormous elasticity and extraordinary lightness.

Maxwell's works caused shock among contemporary scientists. Faraday himself wrote with surprise: “At first I was even scared when I saw such mathematical power applied to the question, but was then surprised to see that the question held up so well.” Despite the fact that Maxwell’s views overturned all the then-known ideas about the propagation of transverse waves and about waves in general, far-sighted scientists understood that the coincidence of the speed of light and electromagnetic waves was a fundamental result, which indicated that it was here that a major breakthrough awaited physics.

Unfortunately, Maxwell died early and did not live to see reliable experimental confirmation of his calculations. International scientific opinion changed as a result of the experiments of Heinrich Hertz, who 20 years later (1886–89) demonstrated the generation and reception of electromagnetic waves in a series of experiments. Hertz not only obtained the correct result in the silence of the laboratory, but passionately and uncompromisingly defended Maxwell’s views. And he didn’t limit himself experimental proof the existence of electromagnetic waves, but also studied their basic properties (reflection from mirrors, refraction in prisms, diffraction, interference, etc.), showing the complete identity of electromagnetic waves with light.

It is curious that seven years before Hertz, in 1879, the English physicist David Edward Hughes (Hughes - D. E. Hughes) also demonstrated to other prominent scientists (among them was also the brilliant physicist and mathematician Georg-Gabriel Stokes) the effect of the propagation of electromagnetic waves in the air. As a result of discussions, scientists came to the conclusion that they see the phenomenon of Faraday electromagnetic induction. Hughes was upset, did not believe himself and published the results only in 1899, when the Maxwell-Hertz theory became generally accepted. This example suggests that in science, persistent dissemination and propaganda of the results obtained is often no less important than the scientific result itself.

Heinrich Hertz summed up the results of his experiments: “The experiments described, at least it seems to me, eliminate doubts about the identity of light, thermal radiation and electrodynamic wave motion.”

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)

10 5 - 10 -3

Frequency Hz)

3 · 10 5 - 3 · 10 11

Source

Oscillatory circuit

Macroscopic vibrators

Stars, galaxies, metagalaxies

Receiver

Sparks in the gap of the receiving vibrator (Hertz vibrator)

Glow of a gas discharge tube, coherer

History of discovery

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

DMV- 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, warming up 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

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.