What conditions are needed for the existence of an electric current. Direct current, its characteristics. Conditions necessary for the existence of an electric current. Series connection of energy consumers
To begin with, let's answer the question of what an electric current is. A simple battery on a table does not generate current by itself. And a flashlight lying on the table will not create a current through its LEDs just like that, for no reason at all. For a current to appear, something must flow somewhere, at least start moving, and for this, the circuit of the LEDs of the flashlight and the battery must be closed. Not for nothing, in the old days the electric current was compared with the movement of a certain charged liquid.
In fact, we now know that electric current is the directed motion of charged particles, and that a charged gas would be a closer analogue to reality, a gas of charged particles moving under the action of electric field... But first things first.
Electric current is the directed movement of charged particles
So, electric current is the movement of charged particles, but even the chaotic movement of charged particles is also movement, but it is not yet a current. Likewise, liquid molecules, which are in thermal motion all the time, do not create flows, because the total displacement of the entire volume of the resting liquid is exactly zero.
For a fluid flow to occur, a total movement must occur, that is, the general movement of the fluid molecules must become directional. So the chaotic movement of molecules will add up with the directional movement of the entire volume, and a flow of the entire volume of the liquid will arise.
The situation is similar with electric current - the directed movement of electrically charged particles is an electric current. The speed of the thermal movement of charged particles, for example, in a metal, is measured in hundreds of meters per second, however, with directional movement, when a certain current is set in the conductor, the speed of the general movement of particles is measured in fractions and units of millimeters per second.
So, if a direct current equal to 10 A flows in a metal conductor with a cross section of 1 sq. Mm, then the average speed of the ordered motion of electrons will be from 0.6 to 6 millimeters per second. This will already be an electric shock. And this slow movement of electrons is enough for a conductor, for example of nichrome, to warm up well, obeying.
Particle speed is not the speed of propagation of an electric field!
Note that the current begins in the conductor almost instantly throughout the entire volume, that is, this "movement" spreads along the conductor at the speed of light, but the movement of the charged particles themselves is 100 billion times slower. You can consider the analogy with a pipe through which a liquid flows.
1. For existence electric current charged particles are needed
Electrons in metals and in vacuum, ions in electrolyte solutions - serve as charge carriers and provide the presence of current in different substances... In metals, electrons are very mobile, some of them can freely move from atom to atom, like a gas filling the space between the nodes of the crystal lattice.
In electron tubes, electrons leave the cathode during thermionic emission, rushing under the action of an electric field to the anode. In electrolytes, molecules disintegrate in water into positively and negatively charged parts, and become ions - free charge carriers in electrolytes. That is, wherever an electric current can exist, there are free charge carriers that can move. This is the first condition for the existence of an electric current - the presence of free charge carriers.
2. The second condition for the existence of an electric current is that external forces must act on the charge
If you now look at a conductor, let's say it is a copper wire, then you can ask yourself: what is needed in order for an electric current to arise in it? There are charged particles, electrons, they are able to move freely.
What will make them move? It is known that an electrically charged particle interacts with an electric field. Therefore, an electric field must be created in the conductor, then a potential will arise at each point of the conductor, a potential difference will take place between the ends of the conductor, and the electrons will move in the direction of the field - in the direction from "-" to "+", that is, in the direction against the vector of the electric field strength. The electric field will accelerate electrons, increasing their (kinetic and magnetic) energy.
As a result, if we consider an electric field simply applied from the outside to the conductor (we placed the conductor in an electric field along the lines of force), then electrons will accumulate at one end of the wire, and a negative charge will appear at this end, and since electrons have shifted from the other end of the wire, then a positive charge will take place on it.
As a result, the electric field of a conductor charged by an externally applied electric field will be in such a direction as to weaken the external electric field by its action.
The process of redistribution of charges will proceed almost instantly, and upon its completion, the current in the conductor will stop. The resulting electric field inside the conductor will become zero, and the strength at the edges will be equal in magnitude, but opposite in the direction to the electric field applied from the outside.
If an electric field in a conductor is created by a direct current source, for example a battery, then such a source will become a source of external forces for the conductor, that is, the source that will create a constant EMF in the conductor and will maintain the potential difference. Obviously, in order for the current to be maintained by a source of external forces, the circuit must be closed.
Sections: Physics
Lesson objectives.
Educational:
formation of students' knowledge about the conditions for the emergence and existence of electric current.
Developing:
development of logical thinking, attention, skills to use the knowledge gained in practice.
Educational:
creating conditions for the manifestation of independence, attentiveness and self-esteem.
Equipment.
- Galvanic cells, battery, generator, compass.
- Cards (attached).
- Demonstration material (portraits of prominent physicists Ampere, Volta; posters “Electricity”, “Electric charges”).
Demonstrations:
- The action of an electric current in a conductor on a magnetic needle.
- Sources of current: galvanic cells, battery, generator.
Lesson plan
1. Organizational moment.
2. Introductory remarks by the teacher.
3. Preparation for the perception of new material.
4. Learning new material.
a) current sources;
b) the action of an electric current;
c) physical operetta "Queen of Electricity";
d) filling in the table “Electric current”;
e) safety measures when working with electrical appliances.
5. Summing up the lesson.
6. Reflection.
7. Homework:
a) Based on the knowledge gained in the OBZH lessons, special technologies, prepare and write down in the notebook a memo "Safety measures when working with electrical appliances"
b) Individual task: Prepare a message on the use of a power source in everyday life and technology.
Lesson summary
1. Organizational moment
Mark the presence of students, name the topic of the lesson, the goal.
2. Introductory remarks by the teacher
We are familiar with the words electricity, electric current from early childhood. Electricity is used in our homes, in transport, in production, in the lighting network.
But what is electric current, what is its nature, is not easy to understand.
The word electricity comes from the word electron, which is translated from Greek as amber. Amber is the fossilized resin of ancient conifers. The word current means the flow or movement of something.
3. Preparation for the perception of new material
Questions of the introductory conversation.
What are the two types of charges in nature? How do they interact?
Answer: There are two types of charges in nature: positive and negative.
The carriers of a positive charge are protons, negative electrons. Likely charged particles repel, oppositely charged particles attract
Is there an electric field around an electron?
Answer: Yes, there is an electric field around the electron.
What are free electrons?
Answer: These are electrons farthest from the nucleus, they can move freely between atoms.
4. Learning new material
a) Sources of current.
There are special devices on the table. What are their names? What are they needed for?
Answer: These are galvanic cells, battery, generator - the general name for current sources. They are necessary for the supply of electrical energy, create an electrical field in the conductor.
We know that there are charged particles, electrons and protons, we know that there are devices called current sources.
b) The action of an electric current.
Tell me, how can we understand that there is an electric current in the circuit, according to what actions?
Answer: Electric current has different types of action:
- Thermal - the conductor through which the electric current flows is heated (electric stove, iron, incandescent lamp, soldering iron).
- The chemical action of the current can be observed when an electric current is passed through a solution of copper sulfate - the release of copper from a solution of sulfate, chromium plating, nickel plating.
- Physiological - the contraction of the muscles of humans and animals, through which an electric current passed.
- Magnetic - when an electric current passes through a conductor, if a magnetic needle is placed next to it, it is capable of deflecting. This action is basic. Demonstration of experience: battery, incandescent lamp, connecting wires, compass.
c) Physical operetta "Queen of Electricity". (Appendix No. 1)
Now the girls of the senior year will present to your attention the operetta "Queen of Electricity". Do not forget the Russian proverb "A fairy tale is a lie, but there is a hint in it, a lesson for good fellows." That is, you not only listen and watch, but also take certain information from it. Your task is to write down as many physical terms that appear in the presentation.
d) Filling in the table “Electric current”. (Appendix No. 2)
Tell me, what is one concept that unites all the terms that you wrote down?
Answer: Electric current.
We proceed to filling in the table "Electric current".
Filling out the table, let's summarize the knowledge gained in the lesson and get new information.
In the process of filling out the table, we draw a conclusion about what conditions are necessary to create an electric current.
- The first condition is the presence of free charged particles.
- The second condition is the presence of an electric field inside the conductor.
e) Safety measures when working with electrical appliances.
Where, in industrial practice, do you encounter the use of electric current? Students' answers.
Answer: When working with electrical appliances.
Forbidden.
- Walk on the ground holding electrical appliances connected to the network. It is especially dangerous to walk barefoot on wet soil.
- Enter the switchboard and other electrical rooms.
- Grasp wires that are dangling, exposed, hanging or lying on the ground.
- Drive nails into the wall where hidden wiring may be located. It is deadly at this moment to be grounded on the central heating batteries, water supply.
- Drill walls in places of possible electrical wiring.
- Paint, whitewash, wash walls with external or hidden live wiring.
- Work with switched on electrical appliances near batteries or water mains.
- Work with electrical appliances, change light bulbs while standing on the bathroom.
- Work with faulty electrical appliances.
- Repair non-powered electrical appliances.
5. Summing up the lesson
Following the laws of physics, time is moving inexorably forward, and our lesson has come to its logical conclusion.
Let's summarize our lesson.
What do you think is electric current?
Answer: Electric current is the directed movement of charged particles.
What conditions are necessary to create an electric current?
Answer: The first condition is the presence of free charged particles.
The second condition is the presence of an electric field inside the conductor.
6. Reflection
7. Homework
a) Based on the knowledge gained in the lessons of life safety, special technologies, prepare and write down in the notebook a memo “Safety measures when working with electrical appliances”.
b) Individual task: Prepare a message on the use of a power source in everyday life and technology. (
Outside forces. Electromotive force and voltage.
External forces are those forces that are different in nature from the forces of an electrostatic field.
These forces can be caused by chemical processes, diffusion of current carriers in an inhomogeneous medium, electric (but not electrostatic) fields generated by time-varying magnetic fields, etc.
EMF is a physical quantity equal to the work performed by external forces when moving a single positive charge along the electrical circuit:
ε = A st. / q Measurement unit - 1 V (Volt)
Voltage is a physical quantity equal to the work performed by external and electrical forces when moving a single positive charge.
U = (A st. + A el.) / Q The unit of measurement is 1 V.
Electrical circuit. Uniform and non-uniform section of the chain.
Uniform and non-uniform chain sections
Homogeneous section of the chain - a section of the chain on which no external forces act (no source of current)
An inhomogeneous section of a circuit is a section of a circuit on which there is a current source.
Electrical circuit
Electrical circuit. External and internal section of the circuit, voltage drop.
Electrical circuit- a set of devices, elements intended for the flow of electric current, electromagnetic processes.
The electrical circuit can be divided into two sections: external and internal.
The external section, or, as they say, the external circuit, consists of one or more receivers of electrical energy, connecting wires and various auxiliary devices included in this circuit.
The inner section, or inner chain, is the source itself.
Voltage drop- a gradual decrease in voltage along the conductor through which an electric current flows, due to the fact that the conductor has an active resistance.
Conductor resistance
Resistance is a value proportional to the length of the conductor l and inversely proportional to its cross-sectional area S
The greater the resistance of the conductor, the worse it conducts electric current, and, conversely, the lower the resistance of the conductor, the easier it is for the electric current to pass through this conductor.
Specific electrical resistance of the conductor ρ [Ohm * m] ρ = RS / l R = ρ * l / S
Ohm's law for a section of a circuit and for a closed circuit
Ohm's law for a section of an electrical circuit - the current strength in a section of an electrical circuit is directly proportional to the voltage and inversely proportional to the resistance of the section.
Ohm's law for a complete electrical circuit - the current in the electrical circuit is directly proportional to the EMF of the source and inversely proportional full resistance circuit (sum of external and internal resistances)
I = ε / (R + r). where R is the resistance of the external section of the circuit,
r - internal resistance.
Series connection of energy consumers
When connected in series, the conductors are connected in series, that is, one after another, while I = const, U = U 1 + U 2 + U 3 + ... + U n and R = R 1 + R 2 + R 3 + ... + R n
Parallel connection of current sources.
Electric current work
The work of electric current A is equal to the product of the value of the moved charge Q by the voltage U
A = Q * U [A] = J, [U] = B, [Q] = Cl, [t] = c.
Because I = Q / t, => Q = I * t, so A = I * U * t
According to Ohm's law for the circuit section I = U / R, U = I * R
A = I * U * T => A = U 2 * t / R (convenient for parallel connection) => A = I 2 * R * t (convenient for serial)
The nature of light.
The nature of light wave.
17th century Christian Huygens: 1) diffraction - light bending around obstacles 2) interference - wave addition.
19th century- Maxwell's theory (speed of light - special case electromagnetic waves) - electromagnetic theory the speed of propagation of electromagnetic waves in a vacuum 3 * 10 8 m / s equal to the speed of light in a vacuum. 299 thousand km / s
17th century O. Römer astronomically obtained the speed of light about 214.3 km / s
19th century... Fizeau the speed of light is about 313 thousand km / s
The nature of light quantum.
about 500 BC Pythagoras: light is a stream of particles.
17th century Isak Newton held the same theory. Carpuscle (from Lat.) - particle.
Newton's carpuscular theory: 1) rectilinear propagation of light 2) the law of reflection 3) the formation of shadows from objects
19 in Heinrich Hertz discovered the phenomenon of the photoelectric effect.
20th century. Light has dual nature - has a corpuscular-wave dualism: during propagation - as a wave, and during radiation and absorption - as a stream of particles.
the relationship between the long wavelength of lambda and the frequency of nude
lambda = s / nu s - speed of light in vacuum [m / s] lambda [m] nu [Hz]
Reflection laws
(1) The incident ray, the reflecting ray, and the perpendicular to the interface between the two media, reconstructed at the point of incidence of the ray, lie in the same plane.
2 Reflection angle γ equal to the angle incidence α: γ = α
Specular reflection - if the roughness is less than lambda and diffuse roughness is comparable to lambda
Diffuse reflection of light. Specular reflection of light.
Light refraction laws.
The law of refraction of light: the incident and refracted rays, as well as the perpendicular to the interface between the two media, reconstructed at the point of incidence of the ray, lie in the same plane. The ratio of the sine of the angle of incidence α to the sine of the angle of refraction γ is a constant value for these two media:
The constant value n is called the relative refractive index of the second medium relative to the first. The refractive index of a medium relative to vacuum is called the absolute refractive index.
The relative refractive index of two media is equal to the ratio of their absolute refractive indices:
The physical meaning of the refractive index is the ratio of the speed of propagation of waves in the first medium υ 1 to the speed of their propagation in the second medium υ 2:
The nature of light from 26.
Wave interference- this is the phenomenon of superposition of coherent waves; characteristic of waves of any nature (mechanical, electromagnetic, etc.)
Coherent waves are waves emitted by sources that have the same frequency and constant phase difference.
When coherent waves are superimposed at any point in space, the amplitude of oscillations (displacement) of this point will depend on the difference in the distances from the sources to the point under consideration. This difference in distance is called travel difference.
When superimposing coherent waves, two limiting cases are possible:
Maximum condition:
where 
The wavelength difference is equal to an integer number of wavelengths (otherwise an even number of half-wavelengths).
In this case, the waves at the point under consideration come with the same phases and amplify each other - the amplitude of the oscillations of this point is maximum and is equal to the doubled amplitude.
Minimum condition:
, where
The difference in wave paths is equal to an odd number of half-wavelengths.
The waves arrive at the considered point in antiphase and cancel each other out.
The vibration amplitude of this point is zero.
As a result of the superposition of coherent waves (wave interference), an interference pattern is formed.
With the interference of waves, the amplitude of the oscillations of each point does not change over time and remains constant.
When incoherent waves are superimposed, there is no interference pattern, since the amplitude of the oscillations of each point changes with time.
Light interference
1802 The English physicist Thomas Jung set up an experiment in which the interference of light was observed.
Thomas Young's experience
Two light beams were formed from one source through slit A (through slits B and C), then light beams fell on screen E. Since the wonders from slits B and C were coherent, an interference pattern could be observed on the screen: alternation of light and dark stripes ...
Light stripes - waves amplified each other (the maximum condition was observed).
Dark stripes - waves formed in antiphase and extinguished each other (minimum condition).
If in Young's experiment a source of monochromatic light was used (of the same wavelength, then only light and dark stripes of this color were observed on the screen.)
If the source gave white light (i.e., complex in its composition), then rainbow stripes were observed on the screen in the area of light stripes. The iridescence was explained by the fact that the conditions of the maxima and minima depend on the wavelengths.
Interference in thin films
The phenomenon of interference can be observed, for example:
Rainbow stains on the surface of the liquid when oil, kerosene spills, in soap bubbles;
The thickness of the film must be greater than the wavelength of the light.
During his experiment, Jung was the first to measure the length of a light wave.
As a result of the experiment, Jung proved that light has wave properties.
Interference application:
- interferometers - devices for measuring the wavelength of light
- antireflection of optics (in optical devices, when light passes through the lens, the loss of light is up to 50%) - all glass parts are covered with a thin film with a refractive index slightly less than that of glass; the interference maxima and minima are redistributed and the loss of light is reduced.
The nature of light from 26.
DIFFRACTION OF LIGHT
Diffraction- This is a phenomenon inherent in wave processes for any kind of waves.
Light diffraction Is the deviation of light rays from rectilinear propagation when passing through narrow slots, small holes or when bending around small obstacles.
The phenomenon of light diffraction proves that light has wave properties.
To observe diffraction, you can:
Pass light from the source through a very small opening or place the screen at a great distance from the opening. Then a complex pattern of light and dark concentric rings is observed on the screen.
- or direct the light onto a thin wire, then light and dark stripes will be observed on the screen, and in the case of white light - a rainbow stripe.
Diffraction grating
It is an optical instrument for measuring the wavelength of light.
A diffraction grating is a collection of a large number of very narrow slits separated by opaque gaps.
If a monochromatic wave is incident on the grating. then the slits (secondary sources) create coherent waves. A collecting lens is placed behind the lattice, then a screen. As a result of the interference of light from various slots of the grating, a system of maxima and minima is observed on the screen.
The path difference between the waves from the edges of adjacent slots is equal to the length of the AC segment. If this segment contains an integer number of wavelengths, then the waves from all the slots will amplify each other. When using white light, all maxima (except for the central one) are rainbow colored.
So the maximum condition is:
where k is the order (or number) of the diffraction spectrum
The more lines are drawn on the grating, the farther from each other are the diffraction spectra and the smaller the width of each line on the screen; therefore, the maxima are seen as separate lines, i.e. the resolving power of the grating increases.
The more grooves per grating unit length, the greater the wavelength measurement accuracy.
LIGHT POLARIZATION
Wave polarization
The property of transverse waves is polarization.
A polarized wave is a transverse wave in which oscillations of all particles occur in one plane.
Light polarization
The tourmaline experiment is proof of the transverse nature of the light waves.
Tourmaline crystal is a transparent, green mineral with an axis of symmetry.
In a ray of light from an ordinary source, there are fluctuations in the vectors of the electric field strength E and magnetic induction B in all possible directions perpendicular to the direction of propagation of the light wave. Such a wave is called a natural wave.
When passing through the tourmaline crystal, the light is polarized.
In polarized light, the oscillations of the intensity vector E occur only in one plane, which coincides with the axis of symmetry of the crystal.
The polarization of light after passing through the tourmaline is detected if a second tourmaline crystal (analyzer) is placed behind the first crystal (polarizer).
With the same directional axes of the two crystals, the light beam will pass through both and will only slightly weaken due to the partial absorption of light by the crystals.
Diagram of the polarizer and the analyzer behind it:
If the second crystal starts to rotate, i.e. shift the position of the axis of symmetry of the second crystal relative to the first, then the beam will gradually go out and go out completely when the position of the axes of symmetry of both crystals becomes mutually perpendicular.
Application of polarized light:
Stepless dimming with two polaroids
- to extinguish glare when photographing (glare is extinguished by placing a polaroid between the light source and the reflecting surface)
To eliminate the glare of the headlights of oncoming cars.
Polaroid, a polarizing filter, one of the main types of optical linear polarizers; is a thin polarizing film, glued to protect against mechanical damage and moisture between two transparent plates (films).
DISPERSION
A ray of white light, passing through a triangular prism, not only deflects, but also decomposes into its constituent colored rays.
This phenomenon was established by Isaac Newton through a series of experiments.
Newton's experiments
Experience in the decomposition of white light into a spectrum:
or 
Newton directed the beam sunlight through a small hole onto a glass prism.
Falling on the prism, the beam was refracted and gave an elongated image on the opposite wall with an iridescent alternation of colors - a spectrum.
Experience in the synthesis (production) of white light:
First, Newton directed the sunbeam onto a prism. Then, collecting the colored rays coming out of the prism with the help of a collecting lens, Newton received a white image of the hole on the white wall instead of the colored strip.
Newton's findings:
The prism does not change the light, but only decomposes it into its components
- light rays, differing in color, differ in the degree of refraction; violet rays are most strongly refracted, less strongly - red
Red light, which is less refracted, has the highest speed, and violet light has the lowest, so the prism decomposes the light.
The dependence of the refractive index of light on its color is called dispersion.
Remember the phrase, the initial letters of the words of which give the sequence of the colors of the spectrum:
"Every Hunter Wants To Know Where The Pheasant Sits."
White light spectrum:
Conclusions:
Prism decomposes light
- white light is complex (composite)
- violet rays are refracted more strongly than red ones.
The color of a light beam is determined by its vibration frequency.
When passing from one medium to another, the speed of light and wavelength change, and the frequency that determines the color remains constant.
The boundaries of the ranges of white light and its components are usually characterized by their wavelengths in vacuum.
White light is a collection of wavelengths between 380 and 760 nm.
Where can you observe the phenomenon of dispersion?
When light passes through a prism
- refraction of light in water droplets, for example, on grass or in the atmosphere when a rainbow forms
- around the lanterns in the fog.
How do you explain the color of any object?
White paper reflects all rays of various colors falling on it.
- a red object reflects only red rays, and absorbs rays of other colors
-
The eye perceives rays of a certain wavelength reflected from an object and thus perceives the color of the object.
Spectral analysis - a set of methods for the qualitative and quantitative determination of the composition of an object, based on the study of the spectra of the interaction of matter with radiation, including the spectra of electromagnetic radiation, acoustic waves, mass and energy distribution elementary particles and etc.
Electric current and conditions for its existence.
Electric current is an ordered, directed, movement of free charges in a conductor.
Direct current is an electric current, the characteristics of which do not change over time.
Conditions for the existence of electric current
For the emergence and maintenance of current in any environment, two conditions must be met:
- the presence of free electric charges in the environment
-creation of an electric field in the environment.
In different environments, different charged particles are carriers of electric current.
The current I is a scalar quantity that characterizes the charge Q passing through the cross-section of the conductor per unit of time. Q = q * N I = Q / t
The strength of the current is measured in amperes and the charge in coulombs. I = [A], Q = [Cl]
Current density - j vector quantity j V q, shows the current strength per unit S section.
j = I / S section Section area S section. measured in square meters
Electric current actions are the phenomena that electric current causes. They can be used to judge the presence of current.
Plating some metals with a thin layer of others (nickel plating, chrome plating, copper plating, silver plating, gilding, etc.) - electroplating
Current strength Effect of current on the human body 0 - 0.5 m. A Absent 0.5 - 2 m. A Loss of sensitivity 2 -10 m. A Pain, muscle contractions 10 -20 m. A Growing effect on muscles, some damage 16 m. A Current, above which a person can no longer free himself from the electrodes 20 -100 m. A Respiratory paralysis 100 m. A - 3 A Fatal ventricular fibrillation (immediate resuscitation is required) More than 3 A Cardiac arrest. (If the shock was brief, the heart can be reanimated.) Severe burns.
Electric current is the ordered movement of charged particles. For the existence of an electric current, the following conditions are necessary: 1. The presence of free electric charges in a conductor; 2. The presence of an external electric field for the conductor.
Do liquids conduct electricity? Electrolytes are solutions of salts, alkalis or acids capable of conducting electric current. The electric current of an electrolyte (liquid) is a directed movement of ions in an electric field. (m = kit)
Compare the experiments carried out in the figures. What do the experiments have in common and how do they differ? To create email fields are used A current source is a device in which some form of energy is converted into electrical energy. Devices that separate charges, that is, create an electric field, are called current sources.
The first electric battery appeared in 1799. It was invented by the Italian physicist Alessandro Volta (1745 - 1827) - the Italian physicist, chemist and physiologist, the inventor of the direct electric current source. His first current source, the "volt pole", was built in strict accordance with his theory of "metallic" electricity. Volta alternately placed several dozen small zinc and silver circles on top of each other, placing paper dipped in salted water between them.
Battery (battery) is the common name for a source of electricity for autonomous power supply of a portable device. It can be a single galvanic cell, a battery or their connection into a battery to increase the voltage.
The battery is a reusable chemical current source. If two carbon electrodes are placed in a salt solution, then the galvanometer does not show the presence of current. If the battery is pre-charged, then it can be used as an independent power source. There are different types of batteries: acidic and alkaline. In them, charges are also separated as a result of chemical reactions. Electric batteries are used for energy storage and autonomous power supply for various consumers.
Sealed small-size batteries (GMA). GMAs are used for small-sized consumers of electrical energy (telephone radio handsets, portable radios, electronic watches, measuring instruments, cell phones, etc.).
An accumulator (from the Latin accumulator - a collector) is a device for storing energy for the purpose of its subsequent use.
Electrophoric machine Until the end of the 18th century, all technical power sources were based on electrification by friction. The most efficient of these sources is the electrophoretic machine (the disks of the machine are driven in rotation in opposite directions. As a result of the friction of the brushes against the disks, charges of the opposite sign accumulate on the conductors of the machine). Mechanical power source - mechanical energy is converted into electrical energy.
Electromechanical generator. The charges are separated by mechanical work. It is used for the production of industrial electricity. Generator (from Lat. Generator - manufacturer) - a device, apparatus or machine that produces a product.
Thermocouple Thermocouple Thermocouple (thermocouple) - two wires of different metals must be soldered from one edge, then heat the junction, then a current arises in them. The charges are separated when the junction is heated. Thermocouples are used in thermal sensors and in geothermal power plants as a temperature sensor. Thermal current source - internal energy is converted into electrical energy
Photocell Solar battery Photocell. When some substances are illuminated with light, a current appears in them, the light energy is converted into electrical energy. In this device, the charges are separated by the action of light. Solar cells are composed of photocells. They are used in solar batteries, light sensors, calculators, video cameras. The energy of light is converted into electrical energy with the help of solar panels.
Classification of current sources Current source Photocell Method of charge separation Application Action of light Solar batteries Heating Thermoelement Measurement of the temperature of junctions Electromechanical performance. Manufacture of mechanical mechanical generator of industrial electric. energ. work Galvanic Chemical Flashlights, cell reaction radios Battery Chemical Automobiles reaction
Current strength is a physical quantity characterizing the action of the current I n Designated by - n Measured in amperes - A n Instrument for measurement - ammeter, connected in series. n The device for regulation is a rheostat.
Why is resistance decreasing? n The distance in the diagram from the tip of the arrow to the pole of the rheostat is the distance that the charge travels along the wire with high resistance. By moving the rheostat slider to the left, we reduce this distance, and, consequently, the resistance of the circuit.
Determination of amperage: Amperage is a physical quantity that shows how much charge has passed through the cross-section of a conductor per unit of time.
Unit of current ANDRE-MARI AMPERE (1775 - 1836) - French physicist and mathematician. The current in the metal conductor is
Voltage is a physical quantity that characterizes the work of an electric field to move a charge. n Indicated by - U Measured in volts - V n Instrument for measuring voltmeter, connected in parallel. n
And again, good day to you, dear. Let's start our today's conversation without unnecessary preludes. It would seem that we figured out the causes of the current in the conductor a long time ago. We placed a conductor in a field - electrons ran, a current appeared. What else does. But it turns out that for this current to exist in the conductor constantly, it is necessary to observe certain conditions. For a clearer understanding of the physics of the process of electric current flow in a conductor, consider an example.
Suppose we have some kind of conductor, which we will place in an electric field as shown in Figure 4.1.
Figure 4.1 - Conductor in an electric field
We conventionally denote the magnitude of the tension at the ends of the conductor as E 1 and E 2, with E 1> E 2. As we found out earlier, free electrons in the conductor will begin to move towards a higher field strength, that is, to point A. However, over time, the potential formed by the accumulation of electrons at point A will become such that its own electromagnetic field E 0 will be equal in magnitude to the external field, and the directions of the fields will be opposite, since the potential of point B is more positive (lack of electrons caused by the action of an external field).
Since the net effect of two identical opposite forces is zero: | E | + | (E 0) | = 0, the electrons stop moving in order, the electric current stops. In order for the flow of electrons to be continuous, it is necessary: firstly, to apply an additional force of a non-potential nature, which would compensate for the influence of the conductor's own electric field and, secondly, to create a closed loop, since the movement of electrons can occur only in conductors (earlier we pointed out that, although dielectrics have some electrical conductivity, they do not transmit electric current) and to ensure the constancy of the compensating force, the constancy of the fields is necessary: both external and intrinsic.
Let's start with the second point. We will consider a conductor placed in a field, as shown in Figure 4.2. Let us assume that after the interaction of the external and own electromagnetic fields has been compensated, we have applied, in addition to the external field, one more field of the same kind. The total action of the external field will be 2 | E |. The current in the conductor will continue to flow in the same direction, but exactly until 2 | E |> | E 0 |, after which the electric current will stop again. That is, the external influence must increase continuously to ensure the flow of current in the open conductor, which is impossible.
If we close the conductor so that one part of it lies outside the field, then due to the work of an additional force in addition to the external field (this force in this case should not be potential, since the work of the potential force in a closed loop is zero and does not depend on the shape of the trajectory), then an electric current will appear in the conductor, due to the influence of only the external field, since the conductor's own field will be completely compensated. That is why any electrical circuit must always be closed.
You can try to explain the need to introduce additional force from the following consideration: if we could partially transfer the charges from end B of the conductor to end A of the conductor, the electric current would also not stop. However, such "landing" also requires energy. This means that the introduction of additional force is still necessary. Non-potential forces are also called outside forces. And their sources are current sources or generators. 
Figure 4.2 - The emergence of its own electromagnetic field in the conductor
So where can we get additional force, which, moreover, should not be created by the field, because without it we will not receive current? It turns out that during the course of a chemical redox reaction, for example, the interaction of lead dioxide and dilute sulfuric acid, free electrons are released:
In order to "attract" all the electrons released during the reaction to one point in space, several lead grids, called electrodes, are placed in the sulfuric acid solution. One part of the electrodes is made of lead and is called the cathode, the other - the anode - is made of lead dioxide. The cathode is the source of free electrodes for the external circuit, and the anode is the receiver.
The given example corresponds to a device known to all motorists (and not only) - a lead-acid battery. Of course, the given example coincides little with what happens inside the battery in reality, however, the essence of the occurrence of current reflects well. Thus, an electric field arises between the positive anode (few electrons) and the negative cathode (many electrons), which forms external forces and creates a current in the conductor. This force depends only on the course of the chemical reaction, then it is practically constant until the moment when the elements of this reaction exist - acid and lead oxide. Therefore, if we remove the electric field and connect the conductor to the anode and cathode, the electric current will still flow due to the fact that the battery creates an external force. The conductor will have its own electric field around it, which must be overcome by the battery in order to transfer an electron from the cathode to the anode. This is the essence of outside power.
Now consider the situation with the battery and the conductor connected to it. The electric field does a positive job of moving a positive charge (we are talking about positive charges, since the direction of their movement corresponds to the direction of the current) in the direction of decreasing the field potential. The current source conducts the separation of electric charges - positive charges accumulate on one pole, negative charges on the other. The strength of the electric field in the source is directed from the positive pole to the negative, so the work of the electric field to move the positive charge will be positive when it moves from "plus" to "minus". The work of external forces, on the contrary, is positive in the event that positive charges move from the negative pole to the positive, that is, from "minus" to "plus". This is the fundamental difference between the concepts of potential difference and EMF, which must always be remembered.
Figure 4.3 shows the direction of current flow I in the conductor connected to the battery - from the positive anode to the negative cathode, however, inside the battery, external forces of the chemical reaction "drop" electrons from the external circuit from the anode to the cathode and positive ions from the cathode to the anode, that is, they act against the direction of movement of the current and the direction of the field. 
Figure 4.3 - Demonstration of external forces in the event of an electric current
From the above considerations, the following conclusion can be drawn: the forces acting on the charge inside the current source are different from the forces acting inside the conductor. Accordingly, it is necessary to distinguish these forces from each other. To characterize external forces, the value of the electromotive force (EMF) was introduced - the work performed by external forces to move a single positive charge. It is denoted by the Latin letter ε ("epsilon") and is measured in the same way as the potential difference - in volts.
Since the potential difference and EMF are forces different types, we can say that the EMF outside the terminals of the source is equal to zero. Although in ordinary life these subtleties are neglected and said: "The voltage on the battery is 1.5V", although strictly speaking, the voltage on the circuit section is the total work of electrostatic and external forces to move a single positive charge. In the future, we will still encounter these concepts and they will be useful to us when calculating complex electrical circuits.
That's probably all, because the lesson turned out to be too loaded ... But the concepts of voltage and EMF need to be able to distinguish.
- For the existence of an electric current, two conditions are necessary:
1) closed electrical circuit;
2) the presence of a source of third-party non-potential forces. - Electromotive force (EMF) is the work performed by external forces to move a single positive charge.
- Sources of external forces in an electrical circuit are also called current sources.
- The positive terminal of the battery is called the anode, the negative terminal is the cathode.
There will be no tasks this time, it is better to repeat this lesson too much in order to understand the whole physics of current flow in a conductor. As always, you can leave any questions, suggestions and wishes in the comments below! Until next time!
