With the words "electricity", " electric charge», « electricity»You have met many times and have gotten used to them. But try to answer the question: "What is an electric charge?" - and you will see that it is not so easy. The fact is that the concept of charge is a basic, primary concept that cannot be reduced at the present level of development of our knowledge to any simpler, elementary concepts.
Let's try first to find out what is meant by the statement: a given body or particle has an electric charge.
You know that all bodies are built from the smallest, indivisible into simpler (as far as science now knows) particles, which are therefore called elementary. All elementary particles have mass and due to this they are attracted to each other according to the law universal gravitation with a force that decreases relatively slowly as the distance between them increases, inversely proportional to the square of the distance. Most of the elementary particles, although not all, in addition, have the ability to interact with each other with a force that also decreases inversely with the square of the distance, but this force is a huge number of times greater than the force of gravity. So. in the hydrogen atom, shown schematically in Figure 91, an electron is attracted to the nucleus (proton) with a force 101 "times greater than the force of gravitational attraction.
If particles interact with each other with forces that slowly decrease with increasing distance and many times exceed the forces of universal gravity, then they say that these particles have an electric charge. The particles themselves are called charged. There are particles without an electric charge, but there is no electric charge without a particle.
Interactions between charged particles are called electromagnetic. Electric charge - physical quantity, which determines the intensity of electromagnetic interactions, just as mass determines the intensity of gravitational interactions.
The electric charge of an elementary particle is not a special "mechanism" in a particle that could be removed from it, decomposed into its component parts and reassembled. The presence of an electric charge in an electron and other particles means only the existence
certain power interactions between them. But we, in essence, do not know anything about the charge if we do not know the laws of these interactions. Knowledge of the laws of interactions should be part of our understanding of the charge. These laws are not simple, it is impossible to state them in a few words. This is why you cannot give satisfactory enough short definition what an electric charge is.
Two signs of electric charges. All bodies have mass and therefore are attracted to each other. Charged bodies can both attract and repel each other. This most important fact, familiar to you from a class VII physics course, means that in nature there are particles with electric charges of opposite signs. With the same signs of the charge, the particles are repelled, and with different signs, they are attracted.
The charge of elementary particles - protons that make up all atomic nuclei, is called positive, and the charge of electrons is called negative. There are no internal differences between positive and negative charges. If the signs of the charges of the particles were reversed, then the nature of the electromagnetic interactions would not change at all.
Elementary charge. In addition to electrons and protons, there are several other types of charged elementary particles. But only electrons and protons can exist indefinitely long in a free state. The rest of the charged particles live for less than a millionth of a second. They are born in collisions of fast elementary particles and, having existed negligibly little, decay, turning into other particles. You will get acquainted with these particles in the X class.
Particles that have no electrical charge include a neutron. Its mass only slightly exceeds the mass of a proton. Neutrons, together with protons, are part of the atomic nucleus.
If an elementary particle has a charge, then its value, as shown by numerous experiments, is strictly definite (one of such experiments - the experiment of Milliken and Ioffe - was described in a textbook for grade VII)
There is a minimum charge, called elementary, which all charged elementary particles have. The charges of elementary particles differ only in signs. It is impossible to separate part of the charge, for example from an electron.
In the Universe, each body lives in its own time and the basic elementary particles as well. The lifetime of most elementary particles is short enough.
Some disintegrate immediately after birth, which is why we call them unstable particles.
They are through a short time decay into stable ones: protons, electrons, neutrinos, photons, gravitons and their antiparticles.
The most important micro-objects in our near space are protons and electrons... Some of the distant parts of the Universe may consist of antimatter, the most important particles there will be antiproton and antielectron (positron).
In total, several hundred elementary particles have been discovered: proton (p), neutron (n), electron (e -), as well as photon (g), pi-mesons (p), muons (m), neutrinos three types(electronic v e, muonic v m, with lepton v t), etc. will obviously bring more new microparticles.
Particle Spawn:
Protons and electrons
The origins of protons and electrons date back to approximately ten billion years.
Another type of micro-objects that play an essential role in the structure of the near space are neutrons, which have a common name with a proton: nucleons. By themselves, neutrons are unstable, they decay about ten minutes after they arise. They can be stable only in the atomic nucleus. A huge number of neutrons are constantly arising in the depths of stars, where the nuclei of atoms are born from protons.
Neutrino
The Universe also constantly produces neutrinos that are similar to an electron, but without charge and with low mass. In 1936, a kind of neutrino was discovered: muonic neutrinos, which arise when protons turn into neutrons, in the interiors of supermassive stars and during the decay of many unstable micro-objects. They are born when cosmic rays collide in interstellar space.
The Big Bang brought about the appearance of a huge number of neutrinos and muon neutrinos. Their number in space is constantly increasing, because they are not absorbed by practically any matter.
Photon
Like photons, neutrinos and muonic neutrinos fill the entire space. This phenomenon is called the "neutrino sea".
Since the time of the Big Bang, a great many photons have remained, which we call relic or fossil photons. The entire outer space is filled with them, and their frequency, and hence the energy, is constantly decreasing, as the Universe is expanding.
At present, all cosmic bodies, primarily stars and nebulae, participate in the formation of the photonic part of the Universe. Photons are born on the surface of stars from the energy of electrons.
Particle bonding
V initial stage formation of the Universe, all basic elementary particles were free. Then there were no nuclei of atoms, no planets, no stars.
Atoms, and of them planets, stars and all substances were formed later, when 300,000 years passed and the incandescent matter cooled down sufficiently during expansion. 
Only the neutrino, muonic neutrino and photon did not enter any system: their mutual attraction is too weak. They remained free particles.
Even at the initial stage of the formation of the Universe (300,000 years after its birth), free protons and electrons combined into hydrogen atoms (one proton and one electron, bound by an electric force).
The proton is considered the main elementary particle with a charge of +1 and a mass of 1.672 · 10 −27 kg (slightly less than 2000 times heavier than an electron). The protons, trapped in a massive star, gradually turned into the main building "iron" of the Universe. At the same time, each of them released one percent of their rest mass. In supermassive stars, which at the end of their life, as a result of their own gravity, are compressed into small volumes, the proton can lose almost a fifth of its rest energy (and hence a fifth of its rest mass).It is known that the "building microblocks" of the Universe are protons and electrons.
Finally, when a proton and an antiproton meet, no system arises, but all their rest energy is released in the form of photons (). 
Scientists argue that as if there is also a ghostly basic elementary particle, graviton, which carries a gravitational interaction similar to electromagnetism. However, the presence of a graviton has been proven only theoretically.
Thus, our Universe, including the Earth, arose and now represent the main elementary particles: protons, electrons, neutrinos, photons, gravitons and many more open and undiscovered micro-objects.
719 Law of Conservation of Electric Charge
720. Bodies with Electric Charges different sign, …
They are attracted to each other.
721. Identical metal balls charged with opposite charges q 1 = 4q and q 2 = -8q brought into contact and moved apart to the same distance. Each of the balls has a charge
q 1 = -2q and q 2 = -2q
723. A droplet with a positive charge (+ 2e) lost one electron when illuminated. The drop charge became equal to
724. Identical metal balls charged with charges q 1 = 4q, q 2 = - 8q and q 3 = - 2q brought into contact and moved apart to the same distance. Each of the balls will have a charge
q 1 = - 2q, q 2 = - 2q and q 3 = - 2q
725. Identical metal balls charged with charges q 1 = 5q and q 2 = 7q brought into contact and moved apart at the same distance, and then brought the second and third balls with charge q 3 = -2q into contact and moved apart at the same distance. Each of the balls will have a charge
q 1 = 6q, q 2 = 2q and q 3 = 2q
726. Identical metal balls charged with charges q 1 = - 5q and q 2 = 7q brought into contact and moved apart to the same distance, and then brought into contact the second and third balls with a charge q 3 = 5q and moved apart to the same distance. Each of the balls will have a charge
q 1 = 1q, q 2 = 3q and q 3 = 3q
727. There are four identical metal balls with charges q 1 = 5q, q 2 = 7q, q 3 = -3q and q 4 = -1q. First, they brought into contact and moved apart the charges q 1 and q 2 (1 system of charges), and then brought into contact the charges q 4 and q 3 (the 2nd system of charges). Then they took one charge from system 1 and 2 and grafted them into contact and moved them to the same distance. These two balls will have a charge
728. There are four identical metal balls with charges q 1 = -1q, q 2 = 5q, q 3 = 3q and q 4 = -7q. First, they brought into contact and moved apart the charges q 1 and q 2 (1 system of charges) and then brought into contact the charges q 4 and q 3 (2 system of charges). Then they took one charge from system 1 and 2 and brought them into contact and moved them apart to the same distance. These two balls will have a charge
729. In an atom, a positive charge has
Core.
730. 8 electrons move around the nucleus of the oxygen atom. The number of protons in the nucleus of an oxygen atom is
731.The electric charge of an electron is
-1.6 10 -19 Cl.
732.The electric charge of a proton is
1.6 10 -19 Cl.
733. The nucleus of a lithium atom contains 3 protons. If 3 electrons revolve around the nucleus, then
The atom is electrically neutral.
734 There are 19 particles in the fluorine nucleus, of which 9 are protons. The number of neutrons in the nucleus and the number of electrons in the neutral fluorine atom
Neutrons and 9 electrons.
735. If in any body the number of protons more numbers electrons, then the body as a whole
Charged positively.
736. A drop with a positive charge of + 3e lost 2 electrons during irradiation. The drop charge became equal to
8 10 -19 Cl.
737. Negative charge in an atom carries
Shell.
738. If an oxygen atom turns into a positive ion, then it
Lost an electron.
739. It has a large mass
Negative hydrogen ion.
740. As a result of friction, 5 × 10 10 electrons were removed from the surface of the glass rod. Electric charge on a stick
(e = -1.6 10 -19 C)
8 · 10 -9 Cl.
741. As a result of friction, the ebony stick received 5 × 10 10 electrons. Electric charge on a stick
(e = -1.6 10 -19 C)
-8 · 10 -9 Cl.
742 Force of the Coulomb interaction of two point electric charges with a decrease in the distance between them by a factor of 2
Will increase by 4 times.
743 Force of the Coulomb interaction of two point electric charges with a decrease in the distance between them by a factor of 4
Will increase 16 times.
744. Two point electric charges act on each other according to the Coulomb's law with a force of 1N. If the distance between them is doubled, then the force of the Coulomb interaction of these charges becomes equal to
745. Two point charges act on each other with a force of 1N. If the magnitude of each of the charges is increased by a factor of 4, then the force of the Coulomb interaction becomes equal to
746. The force of interaction of two point charges is 25 N. If the distance between them is reduced by 5 times, then the force of interaction of these charges will become
747 The force of the Coulomb interaction of two point charges with an increase in the distance between them by a factor of 2
It will decrease by 4 times.
748 The force of the Coulomb interaction of two point electric charges with an increase in the distance between them by a factor of 4
It will decrease 16 times.
749. Coulomb's Law Formula
.
750. If 2 identical metal balls with charges + q and + q are brought into contact and moved apart at the same distance, then the modulus of the interaction force
Will not change.
751. If 2 identical metal balls, having charges + q and -q, bring the balls into contact and push them apart at the same distance, then the force of interaction
Will be equal to 0.
752 Two charges interact in air. If they are placed in water (ε = 81) without changing the distance between them, then the force of the Coulomb interaction
Decrease 81 times.
753.The force of interaction of two charges of 10 nC, located in air at a distance of 3 cm from each other, is equal to
(
)
754 Charges of 1 μC and 10 nC interact in air with a force of 9 mN at a distance
()
755. Two electrons located at a distance of 3 · 10 -8 cm from each other are repelled with a force ( ; e = - 1.6 10 -19 C)
2.56 · 10 -9 N.
756. With an increase in the distance from the charge 3 times, the modulus of the intensity electric field
It will decrease by 9 times.
757. The field strength at the point is 300 N / C. If the charge is 1 · 10 -8 C, then the distance to the point
()
758. If the distance from a point charge creating an electric field increases 5 times, then the strength of the electric field
It will decrease 25 times.
759. The field strength of a point charge at a point is 4 N / C. If the distance from the charge is increased by 2 times, then the intensity will be equal to
760. Specify the formula for the strength of the electric field in the general case.
761 Mathematical notation of the principle of superposition of electric fields
762. What is the formula for the intensity of a point electric charge Q
.
763. The modulus of the electric field strength at the point where the charge is located
1 · 10 -10 C is equal to 10 V / m. The force acting on the charge is
1 · 10 -9 N.
765. If on the surface of a metal ball with a radius of 0.2 m, a charge of 4 · 10 -8 C is distributed, then the charge density
2.5 · 10 -7 C / m 2.
766 In a vertically directed uniform electric field, there is a speck of dust with a mass of 1 · 10 -9 g and a charge of 3.2 · 10-17 C. If the gravity of a dust grain is balanced by the strength of the electric field, then the field strength is
3 · 10 5 N / C.
767 In three vertices of a square with a side of 0.4 m there are identical positive charges of 5 · 10 -9 C. Find tension at the fourth peak
() 540 N / C
768. If two charges 5 · 10 -9 and 6 · 10 -9 C, so that they repel with a force of 12 · 10 -4 N, then they are at a distance
768. If the module of a point charge is reduced by 2 times and the distance to the charge is reduced by 4 times, then the electric field strength at this point
Will increase 8 times.
Decreases.
770. The product of the electron charge by the potential has the dimension
Energy.
771. The potential at point A of the electric field is 100V, the potential at point B is 200V. The work done by the forces of the electric field when moving a charge of 5 mC from point A to point B is equal to
-0.5 J.
772. A particle with charge + q and mass m, located at points of an electric field with strength E and potential, has an acceleration
773 The electron moves in a uniform electric field along the line of tension from a point with a high potential to a point with a lower potential. Its speed at the same time
Increases.
774 An atom with one proton in its nucleus loses one electron. In this case,
Hydrogen ion.
775.Electric field created in vacuum by four point positive charges placed at the vertices of the square with side a. The potential in the center of the square is
776. If the distance from a point charge decreases 3 times, then the field potential
Will increase 3 times.
777. When moving a point electric charge q between points with a potential difference of 12 V, a work of 3 J is performed. In this case, the charge is moved
778. Charge q moved from point electrostatic field to a point with potential. Which of the following formulas:
1) 
2) ; 3) 
You can find work moving the charge.
779 In a uniform electric field with a strength of 2 N / C, a charge of 3 C moves along the lines of force of the field at a distance of 0.5 m. The work of the forces of the electric field on the movement of the charge is
780. The electric field is created by four point opposite charges placed at the vertices of a square with side a. Like charges are located in opposite vertices. The potential in the center of the square is
781. The potential difference between points lying on the same power line at a distance of 6 cm from each other is 60 V. If the field is uniform, then its intensity is
782 Unit of Potential Difference
1 V = 1 J / 1 Cl.
783. Let the charge move in a uniform field with an intensity E = 2 V / m along the line of force 0.2 m. Find the difference between these potentials.
U = 0.4 V.
784. According to Planck's hypothesis, an absolutely black body radiates energy
In portions.
785. The energy of a photon is determined by the formula
1. E = pс 2. E = hv / c 3. E = h 4. E = mc 2. 5. E = hv. 6.E = hc /
1, 4, 5, 6.
786. If the energy of a quantum has doubled, then the radiation frequency
increased by 2 times.
787. If photons with an energy of 6 eV fall on the surface of a tungsten plate, then the maximum kinetic energy of electrons knocked out by them is 1.5 eV. The minimum photon energy at which the photoeffect is possible is for tungsten:
788. Correct statement:
1. The speed of the photon is greater than the speed of light.
2. The speed of a photon in any substance is less than the speed of light.
3. The speed of a photon is always equal to the speed of light.
4. The speed of the photon is greater than or equal to the speed of light.
5. The speed of a photon in any substance is less than or equal to the speed of light.
789. Radiation photons have a large momentum
Blue.
790. When the temperature of the heated body decreases, the maximum radiation intensity
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Elementary particle- the smallest, indivisible, structureless particle.
FUNDAMENTALS OF ELECTRODYNAMICS
Electrodynamics- a branch of physics that studies electromagnetic interactions. Electromagnetic interactions- interactions of charged particles. The main objects of study in electrodynamics are electrical and magnetic fields generated by electric charges and currents.
Topic 1. Electric field (electrostatics)
Electrostatics - a branch of electrodynamics that studies the interaction of stationary (static) charges.
Electric charge.
All bodies are electrified.
Electrifying a body means giving it an electric charge.
Electrified bodies interact - attract and repel.
The more electrified bodies are, the more they interact.
Electric charge is a physical quantity that characterizes the property of particles or bodies to enter into electromagnetic interactions and is a quantitative measure of these interactions.
The totality of all known experimental facts leads to the following conclusions:
· There are two kinds of electric charges, conventionally called positive and negative.
Charges don't exist without particles
· Charges can be transferred from one body to another.
· Unlike body weight, electric charge is not an integral characteristic of a given body. The same body in different conditions may have a different charge.
· The electric charge does not depend on the choice of the frame of reference in which it is measured. The electric charge does not depend on the speed of movement of the charge carrier.
· Like charges repel, unlike charges attract.
Measurement unit in SI - pendant
An elementary particle is the smallest, indivisible particle that has no structure.
For example, in an atom: electron ( , proton ( , neutron ( .
An elementary particle may or may not have a charge: , ,
Elementary charge - the charge belonging to an elementary particle, the smallest, indivisible.
Elementary charge - electron charge modulo.
The charges of an electron and a proton are numerically equal, but opposite in sign:
Electrification of tel.
What does “macroscopic body charged” mean? What determines the charge of any body?
All bodies are composed of atoms, which include positively charged protons, negatively charged electrons and neutral particles - neutrons . Protons and neutrons are part of atomic nuclei, electrons form the electron shell of atoms.
In a neutral atom, the number of protons in the nucleus is equal to the number of electrons in the shell.
Macroscopic bodies consisting of neutral atoms are electrically neutral.
An atom of a given substance can lose one or more electrons or acquire an extra electron. In these cases, a neutral atom turns into a positively or negatively charged ion.
Electrifying bodies– the process of obtaining electrically charged bodies from electrically neutral ones.
Bodies become electrified on contact with each other.
Upon contact, part of the electrons from one body is transferred to another, both bodies are electrified, i.e. receive charges equal in magnitude and opposite in sign:
"Excess" of electrons in comparison with protons creates a "-" charge in the body;
"Lack" of electrons in comparison with protons creates a "+" charge in the body.
The charge of any body is determined by the number of excess or insufficient electrons in comparison with protons.
Charge can be transferred from one body to another only in portions containing an integer number of electrons. Thus, the electric charge of a body is a discrete quantity that is a multiple of the charge of an electron: