Project on the topic of electric current in a vacuum. Presentations for lessons presentation for a physics lesson on the topic. fundamental current in silicon

Lesson on the topic "Electric current in a vacuum."

Objectives of the lesson: to familiarize students with electronic devices - the predecessors of semiconductor devices that still serve today; to achieve students' understanding of the phenomenon of TEE and the conditions for its manifestation; continue to develop attention, logical thinking, and the ability to highlight the main thing.

Equipment: presentation, computer, cathode ray tube, set of vacuum tubes.

Type of lesson - combined (teacher's story using a presentation, self-work with a textbook, control of acquired knowledge)

Lesson plan.

1. Today in class.

2. Repetition of the previous topic “Electric current in a substation” (according to the slide).

3. Teacher’s story about current in a vacuum based on the presentation.

4. Fastening (by slide).

5. Independent work students to consolidate and more in-depth study of the cathode ray tube and the properties of electron beams.

6. D.z. pp. 117 -118 of the 10th grade physics textbook by the authors G. Ya. Myakishev, B. B. Bukhovtsev, N. N. Sotsky.

View document contents
“Presentation for the lesson “Electric current in a vacuum”, grade 10, basic level.”

Electric current in a vacuum

Savvateeva Svetlana Nikolaevna, physics teacher

MBOU "Kemetskaya secondary school", Bologovsky district, Tver region.

Today in class

Is vacuum “nothing” or “something”?

Is vacuum a conductor or a dielectric?

Why do you need a vacuum?

How to introduce charge carriers into a vacuum?

What charge carriers create current in a vacuum?

What devices use current in a vacuum?

What is the main property of a two-electrode electron tube?

Let's repeat

• Why does their resistance decrease with increasing temperature?

A. Decrease conc. free charge carriers.

B . Enlarge conc. free charge carriers.

IN. Enlarge electron speed.

2. Trivalent indium is introduced into tetravalent silicon. What will it be like

main current in silicon?

A. Electronic. B. Hole . IN . Electron-hole.

3. In pure p/p (without impurities), the hole current is 5 A. What is the electronic

Current and total current?

A. 5 A, 5 A . B . 5 A, 10 A . IN. 5 A.0 G . 0.5 A.

4. How does the concentration of free charge carriers change?

For metals and materials when they are heated?

A. For metals it does not change, for metals it increases.

B. For metals it increases, for metals it does not change.

IN . For metals and for metals it increases.

G. For metals and for metals it decreases.

5. What happens when electrons and holes merge?

A. A neutral atom is formed. B. Negative ion.

B. Positive ion.

T SERMOELECTRON EMISSION

• The process of emission of electrons by highly heated metals.
• The intensity depends on the surface area, the temperature of the metal, and the cathode substance.

Electrovacuum diode (two-electrode vacuum tube)

Electric current in a vacuum - directional movement

electrons.

The main property of an electric vacuum diode

The main property of a diode is passes current in one direction.

There is current if at the anode (+ ψ ) or no current if at the anode (-ψ).

This property is used to rectify alternating current.

Cathode ray tube – oscilloscope, TV, computer displays

Properties of electron beams: inertia-free, electrically deflected

And magnetic fields cause some substances to glow and heat up bodies.

Consolidation

• Answers to questions on the slide “Today in class.”
• What is TEE and under what conditions does it occur?
• What is work function?
• Why does a vacuum diode have one-way conductivity?

5. Write a story about the properties of electron beams and about the cathode ray tube.

THERMAL ELECTRON EMISSION. By pumping gas out of a vessel (tube), it is possible to reach a concentration at which the gas molecules have time to fly from one wall of the vessel to the other without ever colliding with each other. This state of gas in the tube is called vacuum. The conductivity of the interelectrode gap in a vacuum can only be ensured by introducing a source of charged particles into the tube.

THERMAL ELECTRON EMISSION. Thermionic emission. Most often, the action of such a source of charged particles is based on the properties of bodies heated to high temperature, emit electrons. This process is called thermionic emission. It can be considered as the evaporation of electrons from the surface of the metal. For many solids, thermionic emission begins at temperatures at which evaporation of the substance itself does not yet occur. Such substances are used to make cathodes.

ONE-WAY CONDUCTION. One-way conduction. The phenomenon of thermionic emission leads to the fact that a heated metal electrode, unlike a cold one, continuously emits electrons. The electrons form an electron cloud around the electrode. The electrode becomes positively charged, and under the influence of the electric field of the charged cloud, electrons from the cloud are partially returned to the electrode.

ONE-WAY CONDUCTION. In the equilibrium state, the number of electrons leaving the electrode per second is equal to the number of electrons returning to the electrode during this time. The higher the temperature of the metal, the higher the density of the electron cloud. The difference between the temperatures of hot and cold electrodes sealed into a vessel from which air is evacuated leads to one-way conduction of electric current between them.

ONE-WAY CONDUCTION. When the electrodes are connected to a current source, an electric field arises between them. If the positive pole of the current source is connected to a cold electrode (anode), and the negative pole to a heated one (cathode), then the electric field strength vector is directed towards the heated electrode. Under the influence of this field, electrons partially leave the electron cloud and move towards the cold electrode. The electrical circuit is closed and a electricity. When the source is turned on in opposite polarity, the field strength is directed from the heated electrode to the cold one. The electric field pushes the cloud's electrons back toward the heated electrode. The circuit appears to be open.

DIODE. Diode. One-way conductivity was previously widely used in electronic devices with two electrodes - vacuum diodes, which, like semiconductor diodes, served to rectify electric current. However, at present, vacuum diodes are practically not used.

“The law of conservation of body momentum” - Man. Law of conservation of momentum. System of interacting bodies. Study the “body impulse”. Nature. Body impulse. Problem solving. Collection of problems. Motivation to learn new material. Direction of the impulse. Study plan physical quantity. Graphic interpretation. Connection of physics with other sciences. Let us consider a system of two interacting bodies. Experimental confirmation of the law. Newton. Complete the drawing.

“Properties of Liquids” - Angle? called the contact angle. Wetting liquids rise through the capillaries, non-wetting liquids descend. But water, for example, does not wet greasy surfaces. And vice versa: liquids that do not wet the capillary will sink into it (glass and mercury). Mercury, on the contrary, will drop below the level in the bowl (right picture). Water almost completely wets the clean glass surface. It turns out that we have constructed a “working model” of the capillary.

“Conductivity of Semiconductors” - Consider the electrical contact of two semiconductors. Different substances have different electrical properties. Conductivity of substances. Half-wave rectifier circuit. Intrinsic conductivity. Semiconductor devices. Questions for control. Intrinsic conductivity of semiconductors. Application of semiconductor diodes. Impurity conductivity of semiconductors. Questions. Semiconductor diode and its application.

"Use of the Atom" - Principle of Receipt nuclear energy. "Atom" is peaceful or military. Peaceful atom for the benefit of humanity. Radioisotope diagnostics in medicine. Nuclear icebreaker. Diagram of the operation of a nuclear power plant. MEPhI reactor. Nuclear medicine. Peaceful "atom". The largest nuclear power plants in Russia.

“Alternative fuels” - Solar energy. Modern fuel substitutes. Alternative fuels. Biofuel. Electricity. Hydrogen. Alcohol. Our present. Garbage recycling process. Compressed air. Types of fuel.

“Body impulse and force impulse” - Law of conservation of impulse. Railway carriage. The law of conservation of momentum using the example of the collision of balls. The concept of body impulse. Learning new material. Preservation. Organizational stage. Summarizing. Change in body momentum. Impulse of force. Consolidation of the studied material. Body impulse. Task. Demonstration of the law of conservation of momentum.

Slide 1

There are no charged particles in a vacuum, and therefore it is a dielectric. Those. it is necessary to create certain conditions that will help produce charged particles. There are free electrons in metals. At room temperature they cannot leave the metal because they are held in it by the forces of Coulomb attraction from positive ions. To overcome these forces, the electron must expend a certain energy, which is called the work function. Energy greater than or equal to the work function can be obtained by electrons when the metal is heated to high temperatures. Made by students 10 A Ivan Trifonov Pavel Romanko

Slide 2


When a metal is heated, the number of electrons with kinetic energy greater than the work function increases, so more electrons are emitted from the metal. The emission of electrons from metals when heated is called thermionic emission. To carry out thermionic emission, a thin wire filament made of refractory metal (incandescent filament) is used as one of the electrodes. A filament connected to a current source becomes hot and electrons fly out from its surface. The emitted electrons enter the electric field between the two electrodes and begin to move directionally, creating an electric current. The phenomenon of thermionic emission underlies the operating principle of electron tubes: vacuum diode, vacuum triode. Electric current in a vacuum Vacuum diode Vacuum triode

Slide 3

Vacuum

Vacuum is a highly discharged gas in which the free path of particles (from collision to collision) is greater than the size of the vessel - electric current is impossible, because the possible number of ionized molecules cannot provide electrical conductivity; - it is possible to create an electric current in a vacuum if you use a source of charged particles; - the action of a source of charged particles can be based on the phenomenon of thermionic emission.

Slide 4

Thermionic emission (TEE)

Thermionic emission (Richardson effect, Edison effect) is the phenomenon of electrons being ejected from a metal at high temperature. is the emission of electrons by solid or liquid bodies when they are heated to temperatures corresponding to the visible glow of a hot metal. A heated metal electrode continuously emits electrons, forming an electron cloud around itself. In an equilibrium state, the number of electrons leaving the electrode is equal to the number of electrons returning to it ( because the electrode becomes positively charged when electrons are lost).The higher the temperature of the metal, the higher the density of the electron cloud.

Slide 5

Vacuum dioid

Electric current in a vacuum is possible in vacuum tubes. A vacuum tube is a device that uses the phenomenon of thermionic emission.

Slide 6

Detailed structure of a vacuum diode

A vacuum diode is a two-electrode (A - anode and K - cathode) electron tube. A very low pressure is created inside the glass container H - a filament placed inside the cathode to heat it. The surface of the heated cathode emits electrons. If the anode is connected to + of the current source, and the cathode to -, then a constant thermionic current flows in the circuit. The vacuum diode has one-way conductivity. Those. current in the anode is possible if the anode potential is higher than the cathode potential. In this case, electrons from the electron cloud are attracted to the anode, creating an electric current in a vacuum.

Slide 7

Current-voltage characteristic of a vacuum diode.

The dependence of current on voltage is expressed by the OABCD curve. When electrons are emitted, the cathode acquires a positive charge and therefore retains electrons near it. In the absence of an electric field between the cathode and the anode, the emitted electrons form an electron cloud at the cathode. As the voltage between the anode and cathode increases, more electrons flow to the anode, and therefore the current increases. This dependence is expressed by the section of the OAB graph. Section AB characterizes the direct dependence of current on voltage, i.e. in the voltage range U1 - U2, Ohm's law is satisfied. The nonlinear dependence in the VCD section is explained by the fact that the number of electrons rushing to the anode becomes greater than the number of electrons escaping from the cathode. When enough great importance voltage U3, all electrons emitted from the cathode reach the anode, and the electric current reaches saturation.

Slide 8

Current-voltage characteristic of a vacuum diode.

A vacuum diode is used to rectify alternating current. As a source of charged particles, you can use a radioactive drug that emits α-particles. Under the influence of electric field forces, α-particles will move, i.e. an electric current will occur. Thus, an electric current in a vacuum can be created by the ordered movement of any charged particles (electrons, ions).

Slide 9

Electron beams

Properties and application: When they come into contact with bodies, they cause heating (electronic melting in a vacuum) They are deflected in electric fields; Deviate at magnetic fields under the influence of the Lorentz force; When a beam hitting a substance is decelerated, X-ray radiation appears; Causes glow (luminescence) of some solids and liquids (luminophores); is a stream of rapidly flying electrons in vacuum tubes and gas-discharge devices.

Slide 10

Cathode ray tube (CRT)

Thermionic emission phenomena and properties of electron beams are used. A CRT consists of an electron gun, horizontal and vertical deflecting electrode plates and a screen. In an electron gun, electrons emitted by a heated cathode pass through the control grid electrode and are accelerated by the anodes. An electron gun focuses an electron beam into a point and changes the brightness of the light on the screen. Deflecting horizontal and vertical plates allow you to move the electron beam on the screen to any point on the screen. The tube screen is coated with a phosphor that begins to glow when bombarded with electrons. There are two types of tubes: 1) with electrostatic control of the electron beam (deflection of the electric beam only by an electric field); 2) with electromagnetic control (magnetic deflection coils are added).

Slide 11

Cathode-ray tube

Application: in TV picture tubes in oscilloscopes in displays

Slide 12

View all slides

Triode. The flow of electrons moving in a vacuum tube from the cathode to the anode can be controlled using electric and magnetic fields. The simplest electric vacuum device in which the flow of electrons is controlled using an electric field is a triode. The container, anode and cathode of a vacuum triode have the same design as that of a diode, however, in the path of electrons from the cathode to the anode in the triode there is a third electrode called a grid. Typically the grid is a spiral of several turns of thin wire around the cathode. If a positive potential is applied to the grid relative to the cathode, then a significant part of the electrons flies from the cathode to the anode, and an electric current exists in the anode circuit. When a negative potential is applied to the grid relative to the cathode, the electric field between the grid and the cathode prevents the movement of electrons from the cathode to the anode, and the anode current decreases. Thus, by changing the voltage between the grid and the cathode, you can regulate the current in the anode circuit.