You have come across the words “electricity”, “electric charge”, “electric current” many times and have managed to get used to them. But try to answer the question: “What is an electric charge?” - and you will see that it is not so simple. The fact is that the concept of charge is a basic, primary concept that cannot be reduced at the current level of development of our knowledge to any simpler, elementary concepts

Let us first try 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 tiny particles, indivisible into simpler (as far as science now knows) particles, which are therefore called elementary. All elementary particles have mass and, due to this, are attracted to each other according to the law of universal gravitation with a force that decreases relatively slowly as the distance between them increases, inversely proportional to the square of the distance. Most elementary particles, although not all, also have the ability to interact with each other with a force that also decreases in inverse proportion to 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, the 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 are many times greater than the forces of gravity, then these particles are said to 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 is a physical quantity that 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 the particle that could be removed from it, decomposed into its component parts and reassembled. The presence of an electric charge on an electron and other particles only means the existence

certain force interactions between them. But we, in essence, do not know anything about charge if we do not know the laws of these interactions. Knowledge of the laws of interactions should be included in our ideas about charge. These laws are not simple; it is impossible to state them in a few words. This is why it is impossible to give a sufficiently satisfactory brief definition of what an electric charge is.

Two signs of electric charges. All bodies have mass and therefore attract each other. Charged bodies can both attract and repel each other. This most important fact, familiar to you from the VII class physics course, means that in nature there are particles with electric charges of opposite signs. If the charge signs are the same, the particles repel, and if they are of different signs, they are attracted.

The charge of elementary particles - protons, which are part of 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 particle charges were reversed, then the nature of 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 in a free state indefinitely. The rest of the charged particles live less than a millionth of a second. They are born during collisions of fast elementary particles and, having existed for an insignificantly short time, decay, turning into other particles. You will become acquainted with these particles in class X.

Neutrons are particles that do not have an electrical charge. Its mass is only slightly greater than 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 numerous experiments have shown, is strictly definite (one of such experiments - the experiment of Millikan and Ioffe - was described in a textbook for grade VII)

There is a minimum charge, called elementary, that all charged elementary particles possess. The charges of elementary particles differ only in signs. It is impossible to separate part of the charge, for example from an electron.

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It is impossible to give a brief definition of charge that is satisfactory in all respects. We are accustomed to finding understandable explanations for very complex formations and processes such as the atom, liquid crystals, the distribution of molecules by speed, etc. But the most basic, fundamental concepts, indivisible into simpler ones, devoid, according to science today, of any internal mechanism, can no longer be briefly explained in a satisfactory way. Especially if objects are not directly perceived by our senses. It is these fundamental concepts that electric charge refers to.

Let us first try to find out not what an electric charge is, but what is hidden behind the statement: this body or particle has an electric charge.

You know that all bodies are built from tiny particles, 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 of universal gravitation, the force of attraction decreases relatively slowly as the distance between them increases: inversely proportional to the square of the distance. In addition, most elementary particles, although not all, have the ability to interact with each other with a force that also decreases in inverse proportion to the square of the distance, but this force is a huge number of times greater than the force of gravity. Thus, in the hydrogen atom, schematically shown in Figure 1, the electron is attracted to the nucleus (proton) with a force 1039 times greater than the force of gravitational attraction.

If particles interact with each other with forces that slowly decrease with increasing distance and are many times greater than the forces of gravity, then these particles are said to 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. When we say that electrons and protons are electrically charged, this means that they are capable of interactions of a certain type (electromagnetic), and nothing more. The lack of charge on the particles means that it does not detect such interactions. Electric charge determines the intensity of electromagnetic interactions, just as mass determines the intensity of gravitational interactions. Electric charge is the second (after mass) most important characteristic of elementary particles, which determines their behavior in the surrounding world.

Thus

Electric charge is a physical scalar quantity that characterizes the property of particles or bodies to enter into electromagnetic force interactions.

Electric charge is symbolized by the letters q or Q.

Just as in mechanics the concept of a material point is often used, which makes it possible to significantly simplify the solution of many problems, when studying the interaction of charges, the concept of a point charge is effective. A point charge is a charged body whose dimensions are significantly less than the distance from this body to the point of observation and other charged bodies. In particular, if they talk about the interaction of two point charges, they thereby assume that the distance between the two charged bodies under consideration is significantly greater than their linear dimensions.

Electric charge of an elementary particle

The electric charge of an elementary particle is not a special “mechanism” in the particle that could be removed from it, decomposed into its component parts and reassembled. The presence of an electric charge on an electron and other particles only means the existence of certain interactions between them.

In nature there are particles with charges of opposite signs. The charge of a proton is called positive, and the charge of an electron is called negative. The positive sign of a charge on a particle does not mean, of course, that it has any special advantages. The introduction of charges of two signs simply expresses the fact that charged particles can both attract and repel. If the charge signs are the same, the particles repel, and if the charge signs are different, they attract.

There is currently no explanation for the reasons for the existence of two types of electric charges. In any case, no fundamental differences are found between positive and negative charges. If the signs of the electric charges of particles changed to the opposite, then the nature of electromagnetic interactions in nature would not change.

Positive and negative charges are very well balanced in the Universe. And if the Universe is finite, then its total electric charge is, in all likelihood, equal to zero.

The most remarkable thing is that the electric charge of all elementary particles is strictly the same in magnitude. There is a minimum charge, called elementary, that all charged elementary particles possess. The charge can be positive, like a proton, or negative, like an electron, but the charge modulus is the same in all cases.

It is impossible to separate part of the charge, for example, from an electron. This is perhaps the most surprising thing. No modern theory can explain why the charges of all particles are the same, and is not able to calculate the value of the minimum electric charge. It is determined experimentally using various experiments.

In the 1960s, after the number of newly discovered elementary particles began to grow alarmingly, it was hypothesized that all strongly interacting particles are composite. More fundamental particles were called quarks. What was striking was that quarks should have a fractional electric charge: 1/3 and 2/3 of the elementary charge. To build protons and neutrons, two types of quarks are enough. And their maximum number, apparently, does not exceed six.

Unit of measurement of electric charge

719. Law of conservation of electric charge

720. Bodies having electric charges of different signs...

They are attracted to each other.

721. Identical metal balls, charged with opposite charges q 1 = 4q and q 2 = -8q, were 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 having a positive charge (+2e) lost one electron when illuminated. The charge of the drop became equal

724. Identical metal balls charged with charges q 1 = 4q, q 2 = - 8q and q 3 = - 2q were 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 were brought into contact and moved apart to the same distance, and then the second and third ball with charge q 3 = -2q were brought into contact and moved apart to 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 were brought into contact and moved apart to the same distance, and then the second and third ball with charge q 3 = 5q were brought into contact 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, the charges q 1 and q 2 (1st system of charges) were brought into contact and moved apart to the same distance, and then the charges q 4 and q 3 (2nd system of charges) were brought into contact. Then they took one charge each 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

728. There are four identical metal balls with charges q 1 = -1q, q 2 = 5q, q 3 = 3q and q 4 = -7q. First, the charges q 1 and q 2 (1 system of charges) were brought into contact and moved apart to the same distance, and then the charges q 4 and q 3 (system 2 of charges) were brought into contact. Then they took one charge each 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.An atom has a positive charge

Core.

730. Eight electrons move around the nucleus of an 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 rotate 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 a neutral fluorine atom

Neutrons and 9 electrons.

735. If in any body the number of protons is greater than the number of electrons, then the body as a whole

Positively charged.

736. A droplet having a positive charge of +3e lost 2 electrons when irradiated. The charge of the drop became equal

8·10 -19 Cl.

737. A negative charge in an atom carries

Shell.

738.If an oxygen atom turns into a positive ion, then it

Lost an electron.

739.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 ebonite rod received 5·10 10 electrons. Electric charge on a stick

(e = -1.6 10 -19 C)

-8·10 -9 Cl.

742.The force of the Coulomb interaction of two point electric charges when the distance between them decreases by 2 times

Will increase 4 times.

743.The force of the Coulomb interaction of two point electric charges when the distance between them decreases by 4 times

Will increase 16 times.

744.Two point electric charges act on each other according to Coulomb’s law with a force of 1N. If the distance between them is increased by 2 times, then the force of the Coulomb interaction of these charges will become equal

745.Two point charges act on each other with a force of 1N. If the magnitude of each charge is increased by 4 times, then the strength of the Coulomb interaction will become equal to

746. The force of interaction between 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 equal

747.The force of the Coulomb interaction of two point charges when the distance between them increases by 2 times

Will decrease by 4 times.

748.The force of the Coulomb interaction of two point electric charges when the distance between them increases by 4 times

Will decrease by 16 times.

749. Formula of Coulomb's law

.

750. If 2 identical metal balls having charges +q and +q are brought into contact and moved apart to the same distance, then the modulus of the interaction force

Will not change.

751. If 2 identical metal balls having charges +q and -q, the balls are brought into contact and moved apart to the same distance, then the interaction force

Will become equal to 0.

752.Two charges interact in the air. If they are placed in water (ε = 81), without changing the distance between them, then the force of the Coulomb interaction

Will decrease by 81 times.

753.The force of interaction between two charges of 10 nC each, located in the 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 repel with a force ( ; e = - 1.6 10 -19 C)

2.56·10 -9 N.

756. When the distance from the charge increases by 3 times, the electric field strength increases

Will decrease by 9 times.

757.The field strength at a 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 electric field strength

Will decrease by 25 times.

759.The field strength of a point charge at a certain point is 4 N/C. If the distance from the charge is doubled, the voltage will become equal to

760.Indicate the formula for the electric field strength in the general case.

761.Mathematical notation of the principle of superposition of electric fields

762.Indicate the formula for the intensity of a point electric charge Q

.

763. Electric field strength modulus 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 equal to

1·10 -9 N.

765. If a charge of 4·10 -8 C is distributed on the surface of a metal ball with a radius of 0.2 m, then the charge density

2.5·10 -7 C/m2.

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 equal to

3·10 5 N/Cl.

767. At the three vertices of a square with a side of 0.4 m there are identical positive charges of 5·10 -9 C each. Find the tension at the fourth vertex

() 540 N/Cl.

768. If two charges are 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 a given point

Will increase 8 times.

Decreases.

770. The product of the electron charge and 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 electric field forces 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 intensity E and potential, has acceleration

773.An electron moves in a uniform electric field along a line of tension from a point with a high potential to a point with a lower potential. Its speed is

Increasing.

774.An atom that has one proton in its nucleus loses one electron. This creates

Hydrogen ion.

775. An electric field in a vacuum is created by four point positive charges placed at the vertices of a square with side a. The potential at the center of the square is

776. If the distance from a point charge decreases by 3 times, then the field potential

Will increase 3 times.

777. When a point electric charge q moves between points with a potential difference of 12 V, 3 J of work is done. In this case, the charge is moved

778.Charge q was moved from a point in the electrostatic field to a point with potential. By which of the following formulas:

1) 2) ; 3) you can find work moving charge.

779. In a uniform electric field of strength 2 N/C, a charge of 3 C moves along the field lines at a distance of 0.5 m. The work done by the electric field forces to move the charge is equal to

780.The electric field is created by four point unlike charges placed at the vertices of a square with side a. Like charges are located at opposite vertices. The potential at the center of the square is

781. The potential difference between points lying on the same field line at a distance of 6 cm from each other is 60 V. If the field is uniform, then its strength is

782.Unit of potential difference

1 V = 1 J/1 C.

783. Let the charge move in a uniform field with intensity E = 2 V/m along a field line of 0.2 m. Find the difference between these potentials.

U = 0.4 V.

784.According to Planck's hypothesis, a completely black body emits energy

In portions.

785. Photon energy is determined by the formula

1. E =pс 2. E=hv/c 3. E=h 4. E=mc2. 5. E=hv. 6.E=hc/

1, 4, 5, 6.

786. If the energy of a quantum has doubled, then the frequency of the radiation

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 the electrons knocked out by them is 1.5 eV. The minimum photon energy at which the photoelectric effect is possible is for tungsten equal to:

788.The following statement is correct:

1. The speed of a 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 a 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 impulse

Blue.

790. When the temperature of a heated body decreases, the maximum radiation intensity

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An elementary particle is 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 electric and magnetic fields created 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.

To electrify a body means to impart an electric charge to it.

Electrified bodies interact - they attract and repel.

The more electrified the bodies are, the stronger 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 allows us to draw the following conclusions:

· There are two types of electric charges, conventionally called positive and negative.

· Charges do not exist without particles

· Charges can be transferred from one body to another.

· Unlike body mass, electric charge is not an integral characteristic of a given body. The same body under different conditions can have a different charge.

· Electric charge does not depend on the choice of reference system in which it is measured. Electric charge does not depend on the speed of the charge carrier.

· Like charges repel, unlike charges attract.

SI unit – pendant

An elementary particle is the smallest, indivisible, structureless particle.

For example, in an atom: electron ( , proton ( , neutron ( .

An elementary particle may or may not have a charge: , ,

Elementary charge is 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 bodies.
What does “a macroscopic body is charged” mean? What determines the charge of any body?

All bodies are made 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 may lose one or more electrons or gain an extra electron. In these cases, the neutral atom turns into a positively or negatively charged ion.

Electrification of bodies– the process of obtaining electrically charged bodies from electrically neutral ones.

Bodies become electrified upon contact with each other.

Upon contact, part of the electrons from one body passes to another, both bodies become electrified, i.e. receive charges equal in magnitude and opposite in sign:
an “excess” of electrons compared to protons creates a “-” charge in the body;
The “lack” of electrons compared to protons creates a “+” charge in the body.
The charge of any body is determined by the number of excess or insufficient electrons compared to 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 electron charge: