Electric current in various environments. Electric current in a vacuum Electric current in a vacuum download presentation
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.
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Presentation on the topic: “Electric current in solutions and melts of electrolytes” Completed by Bazuheir Dalal, 10th grade student
Electric current can flow in five different media: Metals Vacuum Semiconductors Liquids Gases
Liquids according to the degree of electrical conductivity are divided into: dielectrics (distilled water) conductors (electrolytes) semiconductors (molten selenium)
Electric current in liquids Electrolytes are commonly called conducting media in which the flow of electric current is accompanied by the transfer of matter. The carriers of free charges in electrolytes are positively and negatively charged ions. Electrolytes are aqueous solutions of inorganic acids, salts and alkalis.
The resistance of electrolytes decreases with increasing temperature, since the number of ions increases with increasing temperature. Graph of electrolyte resistance versus temperature.
Electrolytic dissociation - during dissolution, collisions between solvent molecules and neutral electrolyte molecules occur as a result of thermal movement. Molecules break down into positive and negative ions. For example, dissolving copper sulfate in water.
The phenomenon of electrolysis is the release of substances included in electrolytes on the electrodes; Positively charged ions (anions) under the influence of an electric field tend to the negative cathode, and negatively charged ions (cations) tend to the positive anode. At the anode, negative ions give up extra electrons (oxidation reaction). At the cathode, positive ions receive the missing electrons (reduction reaction).
Faraday's laws of electrolysis. The laws of electrolysis determine the mass of a substance released during electrolysis at the cathode or anode during the entire period of passage of electric current through the electrolyte. k is the electrochemical equivalent of the substance, numerically equal to the mass of the substance released on the electrode when a charge of 1 C passes through the electrolyte.
Conclusion: 1. charge carriers – positive and negative ions; 2. the process of formation of charge carriers - electrolytic dissociation; 3.electrolytes obey Ohm's law; 4. Application of electrolysis: production of non-ferrous metals (removal of impurities - refining); electroplating - obtaining coatings on metal (nickel plating, chrome plating, gold plating, silver plating, etc.); galvanoplasty - producing peelable coatings (relief copies).
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ELECTRIC CURRENT IN VACUUM
VACUUM In engineering and applied physics, vacuum is understood as a medium containing gas at pressures significantly lower than atmospheric. The main carrier of electric current in a vacuum is the electron.
Thermionic emission is the emission of electrons from solid or liquid bodies when they are heated to temperatures corresponding to the visible glow of hot metal.
To observe thermionic emission, a hollow lamp containing two electrodes can be used: one in the form of a wire made of a refractory material, heated by current (cathode), and the other, a cold electrode that collects thermionic electrons (anode). The anode is most often shaped like a cylinder, inside which the heated cathode is located.
Electrical circuit for observing thermionic emission The circuit contains a diode D, the heated cathode of which is connected to the negative pole of battery B, and the anode to its positive pole; milliammeter mA, which measures the current through the diode D, and a voltmeter V, which measures the voltage between the cathode and the anode. When the cathode is cold, there is no current in the circuit, since the highly discharged gas (vacuum) inside the diode does not contain charged particles. If the cathode is heated using an additional source, the milliammeter will register the appearance of current.
Temperature Dependence A heated metal electrode continuously emits electrons, forming an electron cloud around itself. In an equilibrium state, the number of electrons that left the electrode is equal to the number of electrons that returned to it (since the electrode becomes positively charged when electrons are lost). The higher the temperature of the metal, the higher the density of the electron cloud.
Application Vacuum diode Electron tube Cathode ray tube
A vacuum diode is a two-electrode (A-anode and K-cathode) electron tube. A very low pressure is created inside the glass container. 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 a current in a vacuum. Current-voltage characteristic of a vacuum diode.
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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 of 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.
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“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 effect of such a source of charged particles is based on the property of bodies heated to a high temperature to 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 an electric current is established in it. 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.
