An elementary particle that has no charge. Which micro-objects belong to the main elementary particles

« Physics - Grade 10 "

Let us first consider the simplest case, when electrically charged bodies are at rest.

The section of electrodynamics devoted to the study of the equilibrium conditions for electrically charged bodies is called electrostatics.

What is an electric charge?
What are the charges?

With words electricity, electric charge, electric current you met many times and managed to get used to them. But try to answer the question: “What is an electric charge?” The concept itself charge- this is the main, primary concept, which at the present level of development of our knowledge cannot be reduced 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."

All bodies are built from the smallest particles, which are indivisible into simpler ones and therefore are called elementary.

Elementary particles have mass and due to this they are attracted to each other according to the law of universal gravitation. As the distance between particles increases, the gravitational force decreases in inverse proportion to the square of this distance. Most elementary particles, although not all, also 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 many times greater than the force of gravity.

So in the hydrogen atom, shown schematically in Figure 14.1, the electron is attracted to the nucleus (proton) with a force 10 39 times greater than the force of gravitational attraction.

If the particles interact with each other with forces that decrease with increasing distance in the same way as the forces of universal gravitation, but exceed the forces of gravity many times over, then these particles are said to have an electric charge. The particles themselves are called charged.

There are particles without electric charge, but there is no electric charge without a particle.

The interaction of charged particles is called electromagnetic.

Electric charge 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 of certain force interactions between them.

We, in essence, know nothing about the charge, if we do not know the laws of these interactions. Knowledge of the laws of interactions should be included in our understanding of the charge. These laws are not simple, and it is impossible to state them in a few words. Therefore, it is impossible to give a sufficiently satisfactory concise definition of the concept electric charge.

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, means that in nature there are particles with electric charges of opposite signs; In the case of charges of the same sign, the particles repel, and in the case of different signs, they attract.

Charge of elementary particles - protons, which are part of all atomic nuclei, is called positive, and the charge electrons- 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.

elemental charge.

In addition to electrons and protons, there are several more types of charged elementary particles. But only electrons and protons can exist indefinitely in a free state. The rest of the charged particles live less than millionths of a second. They are born during collisions of fast elementary particles and, having existed for a negligible time, decay, turning into other particles. You will get acquainted with these particles in the 11th grade.

Particles that do not have an electrical charge include neutron. Its mass only slightly exceeds the mass of a proton. Neutrons, along with protons, are part of the atomic nucleus. If an elementary particle has a charge, then its value is strictly defined.

charged bodies Electromagnetic forces in nature play a huge role due to the fact that the composition of all bodies includes electrically charged particles. The constituent parts of atoms - nuclei and electrons - have an electric charge.

The direct action of electromagnetic forces between bodies is not detected, since the bodies in the normal state are electrically neutral.

An atom of any substance is neutral, since the number of electrons in it is equal to the number of protons in the nucleus. Positively and negatively charged particles are connected to each other by electrical forces and form neutral systems.

A macroscopic body is electrically charged if it contains an excess number of elementary particles with any one charge sign. So, the negative charge of the body is due to an excess of the number of electrons in comparison with the number of protons, and the positive charge is due to the lack of electrons.

In order to obtain an electrically charged macroscopic body, i.e., to electrify it, it is necessary to separate part of the negative charge from the positive charge associated with it, or to transfer a negative charge to a neutral body.

This can be done with friction. If you run a comb over dry hair, then a small part of the most mobile charged particles - electrons will pass from the hair to the comb and charge it negatively, and the hair will be charged positively.

Equality of charges during electrification

With the help of experience, it can be proved that when electrified by friction, both bodies acquire charges that are opposite in sign, but identical in magnitude.

Let's take an electrometer, on the rod of which a metal sphere with a hole is fixed, and two plates on long handles: one of ebonite, and the other of plexiglass. When rubbing against each other, the plates become electrified.

Let's bring one of the plates inside the sphere without touching its walls. If the plate is positively charged, then some of the electrons from the needle and the electrometer rod will be attracted to the plate and collect on the inner surface of the sphere. In this case, the arrow will be positively charged and repelled from the electrometer rod (Fig. 14.2, a).

If another plate is introduced inside the sphere, having previously removed the first one, then the electrons of the sphere and the rod will be repelled from the plate and accumulate in excess on the arrow. This will cause the arrow to deviate from the rod, moreover, by the same angle as in the first experiment.

Having lowered both plates inside the sphere, we will not find any deflection of the arrow at all (Fig. 14.2, b). This proves that the charges of the plates are equal in magnitude and opposite in sign.

Electrification of bodies and its manifestations. Significant electrification occurs during friction of synthetic fabrics. When taking off a shirt made of synthetic material in dry air, you can hear a characteristic crackle. Small sparks jump between charged areas of rubbing surfaces.

In printing houses, the paper becomes electrified during printing, and the sheets stick together. To prevent this from happening, special devices are used to drain the charge. However, the electrification of bodies in close contact is sometimes used, for example, in various electrocopying machines, etc.

The law of conservation of electric charge.

Experience with the electrification of plates proves that when electrified by friction, the existing charges are redistributed between bodies that were previously neutral. A small part of the electrons passes from one body to another. In this case, new particles do not appear, and the previously existing ones do not disappear.

When electrifying bodies, law of conservation of electric charge. This law is valid for a system that does not enter from the outside and from which charged particles do not exit, i.e., for isolated system.

In an isolated system, the algebraic sum of the charges of all bodies is conserved.

q 1 + q 2 + q 3 + ... + q n = const. (14.1)

where q 1, q 2, etc. are the charges of individual charged bodies.

The law of conservation of charge has a deep meaning. If the number of charged elementary particles does not change, then the law of charge conservation is obvious. But elementary particles can transform into each other, be born and disappear, giving life to new particles.

However, in all cases, charged particles are produced only in pairs with charges of the same modulus and opposite in sign; charged particles also disappear only in pairs, turning into neutral ones. And in all these cases, the algebraic sum of the charges remains the same.

The validity of the law of conservation of charge is confirmed by observations of a huge number of transformations of elementary particles. This law expresses one of the most fundamental properties of electric charge. The reason for the conservation of charge is still unknown.

With the words "electricity", "electric charge", "electric current" you have met many times and 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 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 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 the smallest, indivisible into simpler (as far as science is now known) 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 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, the electron is attracted to the nucleus (proton) with a force 101" times greater than the force of gravitational attraction.

If the particles interact with each other with forces that slowly decrease with distance and are many times greater than the forces of universal gravitation, then these particles are said to have an electric charge. The particles themselves are called charged. There are particles without 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, which could be removed from it, decomposed into its component parts and reassembled. The presence of an electric charge on an electron and other particles means only the existence

certain force 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 included in our understanding of the 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 concise 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 7th grade physics course, means that in nature there are particles with electric charges of opposite signs. Particles with the same sign of charge repel each other, and with different signs they attract.

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 intrinsic 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.

elemental charge. In addition to electrons and protons, there are several other types of charged elementary particles. But only electrons and protons can exist indefinitely in a free state. The rest of the charged particles live less than millionths of a second. They are born during collisions of fast elementary particles and, having existed for a negligible time, decay, turning into other particles. You will get acquainted with these particles in the X class.

Neutrons are particles that do not have an electric charge. Its mass only slightly exceeds the mass of a proton. Neutrons, along 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 defined (one of these experiments - the experience of Millikan and Ioffe - was described in a textbook for grade VII)

There is a minimum charge, called elementary, which all charged elementary particles possess. 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 short 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 over velocities, and so on. But the most basic, fundamental concepts, indivisible into simpler ones, devoid, according to science today, of any internal mechanism, cannot be briefly explained in a satisfactory way. Especially if the objects are not directly perceived by our senses. It is to such fundamental concepts that the electric charge belongs.

Let us first try to find out not what an electric charge is, but what is hidden behind 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 is now known) 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 inversely with the square of the distance, but this force is a huge number, times greater than the force of gravity. So, in the hydrogen atom, shown schematically in Figure 1, the electron is attracted to the nucleus (proton) with a force 1039 times greater than the force of gravitational attraction.

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 absence of a 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 most important characteristic of elementary particles (after mass), 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 denoted 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 turns out to be effective. A point charge is a charged body whose dimensions are much smaller than the distance from this body to the point of observation and other charged bodies. In particular, if we talk about the interaction of two point charges, then we thereby assume that the distance between the two charged bodies under consideration is much greater than their linear dimensions.

Electric charge of an elementary particle

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 of certain interactions between them.

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

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

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

The most remarkable thing is that the electric charge of all elementary particles is strictly the same in absolute value. There is a minimum charge, called elementary, which 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 amazing thing. No modern theory can explain why the charges of all particles are the same, and cannot calculate the value of the minimum electric charge. It is determined experimentally with the help of various experiments.

In the 1960s, after the number of newly discovered elementary particles began to grow menacingly, a hypothesis was put forward that all strongly interacting particles are composite. The more fundamental particles were called quarks. It turned out to be striking that quarks should have a fractional electric charge: 1/3 and 2/3 of the elementary charge. To construct protons and neutrons, two kinds of quarks are sufficient. And their maximum number, apparently, does not exceed six.

Unit of electric charge

Can you briefly and concisely answer the question: “What is an electric charge?” This may seem simple at first glance, but in reality it turns out to be much more difficult.

Do we know what an electric charge is?

The fact is that at the current level of knowledge, we still cannot decompose the concept of "charge" into simpler components. This is a fundamental, so to speak, primary concept.

We know that this is a certain property of elementary particles, we know the mechanism of interaction of charges, we can measure the charge and use its properties.

However, all this is a consequence of the data obtained empirically. The nature of this phenomenon is still not clear to us. Therefore, we cannot unambiguously determine what an electric charge is.

To do this, it is necessary to open a whole range of concepts. Explain the mechanism of interaction of charges and describe their properties. Therefore, it is easier to figure out what the statement means: "a given particle has (carries) an electric charge."

The presence of an electric charge on a particle

However, later it was possible to establish that the number of elementary particles is much greater, and that the proton, electron and neutron are not indivisible and fundamental building materials of the Universe. They themselves can decompose into components and turn into other types of particles.

Therefore, the name "elementary particle" currently includes a fairly large class of particles smaller in size than atoms and nuclei of atoms. In this case, particles can have a variety of properties and qualities.

However, such a property as an electric charge, there are only two types, which are conditionally called positive and negative. The presence of a charge in a particle is its property to repel or be attracted to another particle, which also carries a charge. The direction of interaction in this case depends on the type of charges.

Like charges repel, unlike charges attract. At the same time, the force of interaction between charges is very large in comparison with the gravitational forces inherent in all bodies without exception in the Universe.

In the nucleus of hydrogen, for example, an electron carrying a negative charge is attracted to a nucleus consisting of a proton and carrying a positive charge with a force 1039 times greater than the force with which the same electron is attracted by a proton due to the gravitational interaction.

Particles may or may not carry a charge, depending on the type of particle. However, it is impossible to “remove” the charge from the particle, just as the existence of a charge outside the particle is also impossible.

In addition to the proton and neutron, some other types of elementary particles carry a charge, but only these two particles can exist indefinitely.

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 brought into contact and moved apart to the same distance. Each ball has a charge

q 1 \u003d -2q and q 2 \u003d -2q

723. A drop that has a positive charge (+2e) loses one electron when illuminated. The charge of the drop 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 \u003d 5q and q 2 \u003d 7q were brought into contact and moved apart to the same distance, and then the second and third balls with charge q 3 \u003d -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 brought into contact the second and third ball with a charge q 3 = 5q and moved apart to the same distance. Each of the balls will have a charge

q 1 \u003d 1q, q 2 \u003d 3q and q 3 \u003d 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 (1 system of charges) were brought into contact and moved apart to the same distance, and then the charges q 4 and q 3 were brought into contact (the 2nd system of charges). Then they took one charge each from system 1 and 2 and grafted 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 were brought into contact (2 systems 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. 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 equal to

-1.6 10 -19 C.

732. The electric charge of a proton is

1.6 10 -19 C.

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 nucleus of fluorine, 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 drop with a positive charge of +3e lost 2 electrons during irradiation. The charge of the drop became equal to

8 10 -19 Cl.

737. A negative charge in an atom carries

Shell.

738. If an oxygen atom has turned 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, an ebonite stick received 5 10 10 electrons. Electric charge on a stick

(e = -1.6 10 -19 C)

-8 10 -9 Cl.

742. The strength of the Coulomb interaction of two point electric charges with a decrease in the distance between them by 2 times

Will increase 4 times.

743. The force of the Coulomb interaction of two point electric charges with a decrease in the distance between them by 4 times

Will increase by 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 becomes equal to

745. Two point charges act on each other with a force of 1N. If the value of each of the charges is increased by 4 times, 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 a factor of 5, then the force of interaction of these charges will become equal to

747. The force of the Coulomb interaction of two point charges with an increase in the distance between them by 2 times

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 4 times

It will decrease by 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 to the same distance, then the modulus of the interaction force

Will not change.

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

Will become 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

It will decrease by 81 times.

753. The force of interaction of 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 at a distance of 3 10 -8 cm from each other repel ; e \u003d - 1.6 10 -19 C)

2.56 10 -9 N.

756

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 that creates an electric field increases 5 times, then the intensity of the electric field

It will decrease by 25 times.

759. Field strength of a point charge at some point 4 N/C. If the distance from the charge is doubled, then the intensity becomes equal to

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

763. Electric field intensity module 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 force of gravity of a dust grain is balanced by the force of the electric field, then the field strength is equal to

3 10 5 N/C.

767. At 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

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

-0.5 J.

772. A particle with charge +q and mass m, located at the points of an electric field with intensity E and potential, has an acceleration

773. An electron moves in a uniform electric field along a line of tension from a point with a higher potential to a point with a lower potential. At the same time, his speed

Increasing.

774. An atom that has one proton in the 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 3 times, then the field potential

Will increase 3 times.

777

778. The charge q was moved from a point of an electrostatic field to a point with a potential. Which of the following formulas:

1) 2) ; 3) you can find work to move the charge.

779. In a uniform electric field with a strength of 2 N / C, a charge of 3 C moves along the field lines of force at a distance of 0.5 m. The work of the electric field forces in moving the charge is

780. An electric field is created by four point charges of opposite names placed at the vertices of a square with side a. Charges of the same name are in 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 \u003d 1 J / 1 C.

783. Let the charge move in a uniform field with 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. Photon energy 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 the electrons knocked out by them is 1.5 eV. The minimum photon energy at which the photoelectric effect is possible for tungsten is:

788. The 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. Photons of radiation have a large momentum

Blue.

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