Oscillating circuit Obtaining electromagnetic fluctuations Presentation. Oscillatory contour. III. Studying a new material


Oscillations are there

mechanical, electromagnetic, chemical, thermodynamic

and different others. Despite such a variety, they all have a lot of things among themselves.


  • A magnetic field

generated by electric shock

basic Physical Characteristic - Magnetic Induction

  • Electric field

creates C I charge

the main physical characteristics

field tension


  • these are periodic or almost periodic charge changes q. , Tok forces I. and voltage U. .

Types of oscillatory

systems

Mathematical

pendulum

Spring

pendulum


Types of oscillatory

systems

Mathematical

pendulum

Spring

pendulum

Oscillatory

Circuit

Scheme of work shock absorber


Schematic representation of types of oscillatory systems

Mathematical pendulum

Spring pendulum



  • this is simplest systemIn which electromagnetic oscillations can occur, consisting of a condenser and coil attached to its plates.

By the nature of the processes causing oscillatory movements

Types of oscillatory

movement

Free

Forced

The oscillatory system is provided to himself, fading oscillations occur due to the initial stock of energy.

Oscillations occur due to external, periodically changing forces.


  • Free oscillations are called fluctuations in the system, which occur after it is removed from the state of equilibrium.
  • Forced oscillations are oscillations in the chain under the action of an external periodic EMF.
  • To bring the system from an equilibrium state, you must inform the condenser an additional charge.
  • The origin of the EMF: the electron is the power of the magnetic field, which causes the change in the magnetic flux and, accordingly, the EMF induction, together with the conductor.

to observe and research the most suitable device is electronic oscilloscope


OSCILLOSCOPE

(from lat. Oscillo - I am swaying and "graph"), measuring

device to observe relationships between two

or several rapidly changing values

(electrical or converted to electrical)

The most common electron-ray oscilloscopes

in which electrical signals,

proportional to the change of the studied values,

enroll plates

oscillographic tube;

on the screen tubes observe or

photograph graphic

image dependence.


L - INDUCTANCE Coils GN


C - Electricity Capacitor F.


CHARGING

Condenser

W- Electric field energy, j


Discharge condenser: The energy of the electric field decreases, but at the same time the energy of the magnetic field of the current increases.

  • W \u003d li ² / 2 -

magnetic field energy, j

i- for power alternating current, BUT


The total energy of the electromagnetic circuit field is equal to the sum of the energy of magnetic and electric fields.

W. = L I. 2 / 2 + Q 2 / 2S.



W el w m w ell

Energy conversion in the oscillatory circuit

q 2/2 C \u003d Q 2/2 C + Li 2/2 \u003d Li 2/2


In real oscillatory circuits

there is always active resistance,

which causes

attenuation of oscillations.



Mechanical and electromagnetic oscillations and oscillatory systems

mechanical and electromagnetic oscillations are subject to completely equal quantitative laws.


In addition to mechanical oscillations in nature, there are and

electromagnetic oscillations.

They are performed in

oscillatory circuit.

It consists of

coils and capacitor.

  • What transformations occur in the circuit

turning energies



  • §27-28,
  • abstract to Tetr.,
  • repeat mechanical oscillations: definitions and physical quantities characterizing oscillations.












Back forward

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Objectives lesson:

  • educational: introduce concepts: "electromagnetic oscillations", "oscillatory contour"; show the universality of the basic patterns of oscillatory processes for oscillations of any physical nature; show that fluctuations in the perfect circuit are harmonic; disclose the physical meaning of the characteristics of the oscillations;
  • developing: Development of cognitive interests, intellectual and creative abilities in the process of acquiring knowledge and skills in physics using various sources of information, including the means of modern information technologies; The formation of skills to evaluate the accuracy of natural science information;
  • educational: Education of conviction in the possibility of knowledge of the laws of nature; use of physics achievements for the benefit of the development of human civilization; The need for cooperation in the process of joint implementation of tasks, preparedness for the moral and ethical assessment of the use of scientific achievements, sense of responsibility for protecting the environment.

During the classes

I. Orgmant.

In today's lesson, we proceed to the study of the new head of the textbook and the theme of today's lesson "electromagnetic oscillations. Oscillatory contour. "

II. Check your homework.

Let's start our lesson from checking homework.

Slide 2. Test on the repetition of material traveled and grade 10.

You were asked to answer the questions to the scheme shown in the picture.

1. With what position the SA2 key is an neon lamp when opening the SA1 key flashes?

2. Why the neon lamp does not flash when the SA1 key is closed, in what position is the SA2 switch?

The test is performed on the computer. One of the student in the meantime collects a scheme.

Answer. The neon lamp flashes during the second position of the SA2 switch: after opening the SA1 key due to the self-induction phenomenon in the coil flows to zero, an alternating magnetic field is excited around the coil, which generates a vortex electric field, which for a short time supports the movement of electrons in the coil. At the top of the chain through the second diode (it is turned on in the bandwidth), short-term current will leak. As a result of self-induction in the coil when operating the chain, the potential difference will appear at its ends (self-induccus), sufficient to maintain the gas discharge in the lamp.

When the SA1 key is closed (SA2 key in position 1) of the voltage of the DC source is not enough to maintain the gas discharge in the lamp, so it does not light up.

Let's check the correctness of your assumptions. The proposed scheme is collected. Let's see what happens with the neon lamp when closing and opening the SA1 key at different positions of the SA2 switch.

(The test is made in the MyTest program. The assessment is set by the program).

File to start the MyTest program (located in the Presentation folder)

Test. (Run the MyTest program, open the "Test" file, press the F5 key to start the test)

III. Studying a new material.

Slide 3.Problem Statement: Let's remember what we know about mechanical oscillations? (The concept of free and forced oscillations, self-oscillating, resonance, etc.) in electrical circuits, as well as in mechanical systems, such as cargo on the spring or pendulum, free oscillations may occur. In today's lesson, we proceed to the study of such systems. The theme of today's lesson: "Electromagnetic oscillations. Oscillatory contour. "

Objectives lesson

  • we introduce the concepts: "electromagnetic oscillations", "oscillatory contour";
  • we show the versatility of the basic patterns of oscillatory processes for oscillations of any physical nature;
  • we show that the oscillations in the perfect circuit are harmonic;
  • we will reveal the physical meaning of the characteristics of oscillations.

Let us first remember what properties should have a system in order for free oscillations in it.

(In the oscillatory system, the returning force should occur and the conversion of energy from one species to another, friction in the system should be quite enough.)

In electrical circuits, as well as in mechanical systems, such as cargo on the spring or pendulum, free oscillations may occur.

What fluctuations are called free oscillations? (Oscillations that occur in the system after eliminating it from the equilibrium position) What fluctuations are called forced oscillations? (oscillations occurring under the action of an external periodically changing EMF)

Periodic or almost periodic changes in charge, current and voltage forces are called electromagnetic oscillations.

Slide 4. After I invented the Leiden Bank and learned to inform her a big charge with the help of an electrostatic machine, began to study the electric discharge of banks. The closure of the ledden bank with the help of a wire coil, found that steel spokes inside the coil are magnetized, but to predict what the end of the coil core will be the North Pole, and which southern it was impossible. A significant role in the theory of electromagnetic oscillations was played by the German scientist of the XIX century Helmgolts Herman Ludwig Ferdinand. He is called the first physician among scientists and the first scientists among doctors. He was engaged in physics, mathematics, physiology, anatomy and psychology, having achieved in each of these regions of world recognition. Having paid attention to the vibrational nature of the discharge of the Leiden bank, in 1869, Helmgoltz showed that similar oscillations occur in an induction coil connected to the capacitor (ie, essentially created an oscillating circuit consisting of inductance and capacity). These experiments played a big role in the development of the theory of electromagnetism.

Slide 4.Typically, electromagnetic oscillations occur with a very large frequency that significantly exceeds the frequency of mechanical oscillations. Therefore, an electronic oscilloscope is very convenient for their observation and research. (Demonstration of the device. The principle of its action on the animation.)

Slide 4.Currently, digital came to replace electronic oscilloscopes. On the principles of their action will tell us ...

Slide 5.Animation "Oscilloscope"

Slide 6. But back to electromagnetic oscillations. The simplest electrical system capable of performing free oscillations is a serial RLC contour. The oscillatory contour is called an electrical circuit consisting of a sequentially connected capacitor with a power capacity of C, the coil with the inductance L and electrical resistance R. We will call it a consecutive RLC-contour.

Physical experiment. We have a chain, the diagram of which is shown in Figure 1. Attach the galvanometer to the coil. We observe the behavior of the electroplating arrow after translating the switch from position 1 to position2. You noticed that the arrow begins to fluctuate, but these oscillations will soon fade. All real contours contain electrical resistance R. For each period of oscillations, part of the electromagnetic energy stored in the circuit turns into jowle heat, and the oscillations become decaying. The graph of sputtering oscillations is considered.

How do free oscillations occur in the oscillatory circuit?

Consider the case when the resistance r \u003d 0 (model of the perfect oscillatory circuit). What processes occur in the oscillatory circuit?

Slide 7. Animation "oscillatory contour."

Slide 8.Let us turn to the quantitative theory of processes in the oscillatory circuit.

Consider a serial RLC contour. When K key is in position 1, the capacitor is charged to the voltage. After switching the key to position 2, the process of dischargeing a condenser through a resistor R and the inductor of the inductance L. under certain conditions, this process may have a oscillating character.

Ohm's law for a closed RLC circuit that does not contain an external current source is recorded as

where - the voltage on the condenser, q - the charge of the condenser, - Current in the chain. On the right side of this ratio costs EMF self-induction of the coil. If the value of the capacitor Q (T) is as a variable, the equation describing the free oscillations in the RLC circuit can be given to the following form:

Consider the case when there is no loss of electromagnetic energy in the circuit (R \u003d 0). We introduce the designation: . Then

(*)

Equation (*) is the main equation describing free oscillations in the LC-circuit (ideal oscillatory circuit) in the absence of attenuation. According to the form, it coincides with the equation of free vibrations of cargo on the spring or thread in the absence of friction forces.

This equation I was recorded when studying the topic "Mechanical oscillations".

In the absence of attenuation, free fluctuations in the electrical circuit are harmonic, that is, they occur by law

q (T) \u003d Q m cos (0 T + 0).

Why? (Since this is the only function of the second derivative of which is equal to the function itself. In addition, Cos0 \u003d 1, and therefore Q (0) \u003d Q m)

The amplitude of the oscillating oscillating q m and the initial phase 0 are determined by the initial conditions, that is, by the way that the system has been removed from the equilibrium state. In particular, for the process of oscillations, which will begin in the circuit shown in Figure 1, after switching the key K to position 2, q m \u003d c, 0 \u003d 0.

Then the equation of harmonic oscillations of charge for our contour will take the form

q (T) \u003d Q m cos 0 t.

The strength of the current also makes harmonic oscillations:

Slide 9.Where is the amplitude of the fluctuations in the current strength. Current fluctuations are ahead of phase on charge fluctuations.

With free oscillations, the periodic transformation of the electrical energy W e, stored in the condenser, into magnetic energy W M coil and vice versa. If there is no energy loss in the oscillatory circuit, then the complete electromagnetic energy of the system remains unchanged:

Slide 9. The parameters L and C of the oscillating circuit define only their own frequency of free oscillations.

.

Considering that, we get.

Slide 9.Formula Thomson's formula, British physics of William Thomson (Lord Kelvin), who brought it in 1853.

Obviously, the period of electromagnetic oscillations depends on the inductance of the coil L and the capacitance of the Cancer C. We have a coil, the inductance of which can be increased by an iron core, and a capacitor of the variable container. Let's first remember how to change the capacity of such a condenser. I remind you, this is the material of the course of grade 10.

The condenser variable containers consists of two sets of metal plates. When rotating the knob of the plate of one dialing is taken into the gaps between the plates of another set. In this case, the capacitance of the capacitor changes in proportion to the change in the area of \u200b\u200bthe overlapping part of the plates. If the plates are connected in parallel, then, by increasing the area of \u200b\u200bthe plates, we will increase the container of each of the capacitors, and therefore the capacity of the entire capacitors will increase the capacity. With a consistent connection of capacitors in the battery, an increase in the capacitance of each capacitor will include a decrease in the capacity of the capacitors battery.

Let's see how the period of electromagnetic oscillations depends on the capacitor C capacitor C and the inductance of the coil L.

Slide 9. Animation "The dependence of the period of electromagnetic oscillations from L and C"

Slide 10.Compare now electrical oscillations and cargo oscillations on the spring. Open the tutorial page 85, Figure 4.5.

The figure shows graphs of the change of charge Q (T) of the capacitor and the shift X (T) of the cargo from the position of the equilibrium, as well as the current charts I (T) and the cargo speed v. (t) in one period T oscillations.

You have a table on your tables that we filled in when studying the topic "Mechanical oscillations". Appendix 2.

One line of this table is filled with you. Taking advantage of Figure 2, paragraph 29 of the textbook and Figure 4.5 on the textbook page 85 fill out the remaining table lines.

What are the processes of free electrical and mechanical oscillations? Let's see the following animation.

Slide 11. Animation "Analogy between electric and mechanical oscillations"

The resulting comparisons of free cargo oscillations on the spring and processes in the electrical oscillatory circuit make it possible to conclude about the analogy between electrical and mechanical values.

Slide 12.These analogies are presented in the table. Appendix 3.

The same table is available on your tables and in the textbook on page 86.

So, the theoretical part we looked at. Did you all understand? Maybe someone has any questions?

Now let's turn to solving problems.

IV. Fizkultminutka.

V. Fixing the studied material.

Solving tasks:

  1. tasks 1, 2, problems of part A No. 1, 6, 8 (orally);
  2. tasks No. 957 (response 5.1 μH), No. 958 (the answer will decrease in 1, 25 times) (at the board);
  3. the task of part in (orally);
  4. task number 1 part with (at the board).

Tasks are taken from the collections of tasks for the 10-11 classes A.P. Rymkiewicz and applications 10. Appendix 4.

Vi. Reflection.

Students fill the reflective card.

VII. Summing up the lesson.

Is the objective of the lesson achieved? Summing up the lesson. Evaluation of students.

VIII. Task at home.

Paragraphs 27 - 30, No. 959, 960, the remaining tasks from Annex 10.

Literature:

  1. Multimedia Course of Physics "Open Physics" version 2.6 Edited by Professor MFTI S.M. Goat
  2. Problem 10-11 class. A.P. Rymkevich, Moscow "Education", 2012.
  3. Physics. Tutorial for 11 class of general educational institutions. G. Y. Mikishev, B.B. Bukhovtsev, V.M. Charugine. Moscow "Enlightenment", 2011.
  4. Electronic application to the textbook G. Y. Mikisheva, B.B. Bukhovtseva, V.M. Charugin. Moscow "Enlightenment", 2011.
  5. Electromagnetic induction. Qualitative (logical) tasks. Grade 11, FizmatProfil. CM. Novikov. Moscow "Clean ponds", 2007. Library "On September 1st". Series "Physics". Issue 1 (13).
  6. http://pitf.ftf.nstu.ru/resources/walter-fendt/osccirc

P.S.If there is no possibility to provide each student a computer, then the test can be held in writing.

"Free oscillations" - Unlucky oscillations. Free electromagnetic oscillations. Where I and Q are the current and electrical charge at any time. According to the electromagnetic induction; the total electromagnetic energy of the oscillatory circuit. The number of oscillations per unit of time is called the frequency of oscillations: full energy.

"Mechanical resonance" - 1. Chain Egyptian bridge in St. Petersburg. Resonance in the technique. 3. Mexico City 1985 Thamsky suspension bridge. The positive value of the resonance frequency meter. 2. State general Education Gymnasium No. 363 of the Frunzensky district. Mechanical tongue frequency - device for measuring the frequency of oscillations.

"Frequency of oscillations" - Sound waves. Think ???? Infrasure is used in military business, fishing fishery, etc. Can the sound spread in gases, liquids, solids? What does the volume of the sound depend on? What does the height of the sound depend on? Sound speed. Ultrasound. In this case, the oscillation of the sound source is obvious.

"Mechanical oscillations" - transverse. Spring pendulum. Oscillatory movement. Free. Longitudinal. "Oscillations and waves." Harmonic. Free oscillations. Waves - the spread of oscillations in space over time. Performed: student of the 11th grade "A" Oleinikova Julia. Forced oscillations. Waves. Mathematical pendulum.

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Signatures for slides:

Oscillatory contour. Electromagnetic oscillations. Radiocommunication Principle and Television Lesson No. 51

Eutergenic oscillations are periodic changes with the time of electrical and magnetic values \u200b\u200b(charge, current, voltage, voltage, magnetic induction, etc.) in the electrical circuit. As is known, to create a powerful electromagnetic wave, which could be registered with devices at large distances from the radiating antenna, it is necessary that the wave frequency is not less than 0.1 MHz.

One of the main parts of the generator is an oscillatory circuit - this is an oscillatory system consisting of a sequentially connected coil with an inductance L, capacitor with a container C and a resistor resistance R.

After I invented the Leiden Bank (the first capacitor) and learned to inform her of a large charge with the help of an electrostatic machine, began to study the electric discharge banks. The closure of the ledden jar with the help of the coil, found that steel spokes inside the coil magnetize. It was strange that it was impossible to predict what the end of the coil core would be the North Pole, and what southern. It was not immediately understood that when the condenser was discharged through a coil in an electrical circuit, oscillations occur.

The period of free oscillations is equal to its own period of the oscillatory system, in this case the contour period. The formula for determining the period of free electromagnetic oscillations was obtained by English physicist William Thomson in 1853

The Popov transmitter diagram is quite simple - this is an oscillatory circuit, which consists of inductance (secondary winding of the coil), the feed battery and the tank (spark gap). If you click on the key, then in the spark gap of the coil, the spark is sparking, causing electromagnetic oscillations in the antenna. The antenna is an open vibrator and emits electromagnetic waves, which, reaching the antenna of the receiving station, excise electrical oscillations in it.

To register the adopted waves, Alexander Stepanovich Popov applied a special device - coherer (from the Latin word "coherence" - clutch) consisting of a glass tube in which metal sawdust is located. On March 24, 1896, the first words were transferred with the help of ABC Morse - "Heinrich Hertz".

Although modern radio receivers are very little reminiscent of Popov receiver, the basic principles of their action are the same.

The main conclusions are: - the oscillating circuit is a oscillatory system consisting of a consecutive coil, capacitor and active resistance. - Free electromagnetic oscillations are oscillations occurring in an ideal oscillatory circuit due to the expenditure reported by this contour of the energy, which is not replenished in the future. - The period of free electromagnetic oscillations can be calculated using the Thomson formula. - From this formula, it follows that the period of the oscillating circuit is determined by the parameters of the components of its elements: the inductance of the coil and the capacitance of the capacitor. - Radio communication is the process of transferring and receiving information using electromagnetic waves. - amplitude modulation is the process of changing the amplitude of high-frequency oscillations with a frequency equal to the frequency of the sound signal. - The process, reverse modulation is called detection.

 

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