Until the beginning of the 20th century, scientists believed that an atom was the smallest indivisible particle of matter, but this turned out to be wrong. In fact, at the center of the atom is its nucleus with positively charged protons and neutral neutrons, and negatively charged electrons rotate in orbitals around the nucleus (this model of the atom was proposed in 1911 by E. Rutherford). It is noteworthy that the masses of protons and neutrons are almost equal, but the mass of an electron is about 2000 times less.

Although an atom contains both positively and negatively charged particles, its charge is neutral, because an atom has the same number of protons and electrons, and differently charged particles neutralize each other.

Later, scientists found out that electrons and protons have the same amount of charge, equal to 1.6 10 -19 C (C is a coulomb, a unit of electric charge in the SI system.

Have you ever thought about the question - what number of electrons corresponds to a charge of 1 C?

1/(1.6·10 -19) = 6.25·10 18 electrons

Electric power

Electric charges influence each other, which manifests itself in the form electric force.

If a body has an excess of electrons, it will have a total negative electrical charge, and vice versa - if there is a deficiency of electrons, the body will have a total positive charge.

By analogy with magnetic forces, when like-charged poles repel and oppositely charged poles attract, electric charges behave in a similar way. However, in physics it is not enough to simply talk about the polarity of an electric charge; its numerical value is important.

To find out the magnitude of the force acting between charged bodies, it is necessary to know not only the magnitude of the charges, but also the distance between them. The force of universal gravitation has already been considered previously: F = (Gm 1 m 2)/R 2

• m 1, m 2- body masses;
• R- the distance between the centers of the bodies;
• G = 6.67 10 -11 Nm 2 /kg- universal gravitational constant.

As a result of laboratory experiments, physicists derived a similar formula for the force of interaction of electric charges, which was called Coulomb's law:

F = kq 1 q 2 /r 2

• q 1, q 2 - interacting charges, measured in C;
• r is the distance between charges;
• k - proportionality coefficient ( SI: k=8.99·10 9 Nm 2 Cl 2; SSSE: k=1).

• k=1/(4πε 0).
• ε 0 ≈8.85·10 -12 C 2 N -1 m -2 - electrical constant.

According to Coulomb's law, if two charges have the same sign, then the force F acting between them is positive (the charges repel each other); if the charges have opposite signs, the acting force is negative (charges attract each other).

How enormous the force of a charge of 1 C is can be judged using Coulomb's law. For example, if we assume that two charges, each 1 C, are spaced at a distance of 10 meters from each other, then they will repel each other with force:

F = kq 1 q 2 /r 2 F = (8.99 10 9) 1 1/(10 2) = -8.99 10 7 N

This is a fairly large force, roughly comparable to a mass of 5600 tons.

Let's now use Coulomb's law to find out at what linear speed the electron rotates in a hydrogen atom, assuming that it moves in a circular orbit.

According to Coulomb's law, the electrostatic force acting on an electron can be equated to the centripetal force:

F = kq 1 q 2 /r 2 = mv 2 /r

Taking into account the fact that the mass of the electron is 9.1·10 -31 kg, and the radius of its orbit = 5.29·10 -11 m, we obtain the value 8.22·10 -8 N.

Now we can find the linear speed of the electron:

8.22·10 -8 = (9.1·10 -31)v 2 /(5.29·10 -11) v = 2.19·10 6 m/s

Thus, the electron of the hydrogen atom rotates around its center at a speed of approximately 7.88 million km/h.

If you rub a glass rod on a sheet of paper, the rod will acquire the ability to attract leaves of the “sultan” (see Fig. 1.1), fluff, and thin streams of water. When you comb dry hair with a plastic comb, the hair is attracted to the comb. In these simple examples we meet with the manifestation of forces that are called electrical.

Rice. 1.1. Attracting the leaves of the “sultan” with an electrified glass rod.

Bodies or particles that act on surrounding objects with electrical forces are called charged or electrified. For example, the glass rod mentioned above, after being rubbed on a piece of paper, becomes electrified.

Particles have an electrical charge if they interact with each other through electrical forces. Electrical forces decrease with increasing distance between particles. Electrical forces are many times greater than universal gravity.

Electric charge- This physical quantity, which determines the intensity of electromagnetic interactions. Electromagnetic interactions are interactions between charged particles or bodies.

Electric charges are divided into positive and negative. Stable elementary particles have a positive charge - protons And positrons, as well as ions of metal atoms, etc. Stable negative charge carriers are electron And antiproton.

There are electrically uncharged particles, that is, neutral ones: neutron, neutrino. These particles do not participate in electrical interactions, since their electric charge is zero. There are particles without an electric charge, but an electric charge does not exist without a particle.

Positive charges appear on glass rubbed with silk. Ebonite rubbed on fur has negative charges. Particles repel when charges have the same signs ( charges of the same name), and with different signs ( unlike charges) particles are attracted.

All bodies are made of atoms. Atoms consist of a positively charged atomic nucleus and negatively charged electrons that move around the atomic nucleus. The atomic nucleus consists of positively charged protons and neutral particles - neutrons. The charges in an atom are distributed in such a way that the atom as a whole is neutral, that is, the sum of the positive and negative charges in the atom is zero.

Electrons and protons are part of any substance and are the smallest stable elementary particles. These particles can exist in a free state for an unlimited time. The electric charge of an electron and a proton is called the elementary charge.

Elementary charge- this is the minimum charge that all charged elementary particles have. The electric charge of a proton is equal in absolute value to the charge of an electron:

E = 1.6021892(46) * 10 -19 C The magnitude of any charge is a multiple in absolute value of the elementary charge, that is, the charge of the electron. Electron translated from Greek electron - amber, proton - from Greek protos - first, neutron from Latin neutrum - neither one nor the other.

Conductors and dielectrics

Electric charges can move. Substances in which electric charges can move freely are called conductors. All metals are good conductors (type I conductors), aqueous solutions salts and acids - electrolytes(type II conductors), as well as hot gases and other substances. The human body is also a conductor. Conductors have high electrical conductivity, that is, they conduct electric current well.

Substances in which electric charges cannot move freely are called dielectrics(from English dielectric, from Greek dia - through, through and English electric - electric). These substances are also called insulators. The electrical conductivity of dielectrics is very low compared to metals. Good insulators are porcelain, glass, amber, ebonite, rubber, silk, gases at room temperatures and other substances.

The division into conductors and insulators is arbitrary, since conductivity depends on various factors, including temperature. For example, glass insulates well only in dry air and becomes a poor insulator when the air humidity is high.

Conductors and dielectrics play a huge role in modern applications of electricity.

DEFINITION

Proton called a stable particle belonging to the class of hadrons, which is the nucleus of a hydrogen atom.

Scientists disagree on which scientific event should be considered the discovery of the proton. An important role in the discovery of the proton was played by:

1. creation of a planetary model of the atom by E. Rutherford;
2. discovery of isotopes by F. Soddy, J. Thomson, F. Aston;
3. observations of the behavior of the nuclei of hydrogen atoms when they are knocked out by alpha particles from nitrogen nuclei by E. Rutherford.

The first photographs of proton tracks were obtained by P. Blackett in a cloud chamber while studying the processes of artificial transformation of elements. Blackett studied the process of capture of alpha particles by nitrogen nuclei. In this process, a proton was emitted and the nitrogen nucleus was converted into an isotope of oxygen.

Protons, together with neutrons, are part of the nuclei of all chemical elements. The number of protons in the nucleus determines atomic number element in periodic table DI. Mendeleev.

A proton is a positively charged particle. Its charge is equal in magnitude to the elementary charge, that is, the value of the electron charge. The charge of a proton is often denoted as , then we can write that:

It is currently believed that the proton is not an elementary particle. It has a complex structure and consists of two u-quarks and one d-quark. The electric charge of a u-quark () is positive and it is equal to

The electric charge of a d-quark () is negative and equal to:

Quarks connect the exchange of gluons, which are field quanta; they endure strong interaction. The fact that protons have several point scattering centers in their structure is confirmed by experiments on the scattering of electrons by protons.

The proton has a finite size, which scientists are still arguing about. Currently, the proton is represented as a cloud that has a blurred boundary. Such a boundary consists of constantly emerging and annihilating virtual particles. But in most simple tasks A proton, of course, can be considered a point charge. The rest mass of a proton () is approximately equal to:

The mass of a proton is 1836 times greater than the mass of an electron.

Protons take part in all fundamental interactions: strong interactions unite protons and neutrons into nuclei, electrons and protons join together in atoms using electromagnetic interactions. As a weak interaction, we can cite, for example, the beta decay of a neutron (n):

where p is proton; — electron; - antineutrino.

Proton decay has not yet been obtained. This is one of the important modern tasks physics, since this discovery would be a significant step in understanding the unity of the forces of nature.

Examples of problem solving

EXAMPLE 1

Exercise	The nuclei of the sodium atom are bombarded with protons. What is the force of electrostatic repulsion of a proton from the nucleus of an atom if the proton is at a distance m. Consider that the charge of the nucleus of a sodium atom is 11 times greater than the charge of a proton. The influence of the electron shell of the sodium atom can be ignored.
Solution	As a basis for solving the problem, we will take Coulomb’s law, which can be written for our problem (assuming the particles are pointlike) as follows: where F is the force of electrostatic interaction of charged particles; Cl is the proton charge; - charge of the nucleus of the sodium atom; - dielectric constant of vacuum; - electrical constant. Using the data we have, we can calculate the required repulsive force:
Answer	N

EXAMPLE 2

If you are familiar with the structure of an atom, then you probably know that an atom of any element consists of three types of elementary particles: protons, electrons, and neutrons. Protons combine with neutrons to form an atomic nucleus. Since the charge of a proton is positive, the atomic nucleus is always positively charged. the atomic nucleus is compensated by the cloud of other elementary particles surrounding it. The negatively charged electron is the component of the atom that stabilizes the charge of the proton. Depending on the surrounding atomic nucleus, an element can be either electrically neutral (in the case of an equal number of protons and electrons in the atom) or have a positive or negative charge (in the case of a deficiency or excess of electrons, respectively). An atom of an element that carries a certain charge is called an ion.

It is important to remember that it is the number of protons that determines the properties of elements and their position in periodic table them. D. I. Mendeleev. The neutrons contained in the atomic nucleus have no charge. Due to the fact that protons are correlated and practically equal to each other, and the mass of the electron is negligible compared to them (1836 times less), the number of neutrons in the nucleus of an atom plays a very important role, namely: it determines the stability of the system and the speed of the nuclei. Contents neutrons determine the isotope (variety) of an element.

However, due to the discrepancy between the masses of charged particles, protons and electrons have different specific charges (this value is determined by the charge ratio elementary particle to its mass). As a result, the specific charge of the proton is 9.578756(27)·107 C/kg versus -1.758820088(39)·1011 for the electron. Due to the high specific charge, free protons cannot exist in liquid media: they can be hydrated.

The mass and charge of a proton are specific values ​​that were established at the beginning of the last century. Which scientist made this - one of the greatest - discoveries of the twentieth century? Back in 1913, Rutherford, based on the fact that the masses of all known chemical elements are greater than the mass of the hydrogen atom by an integer number of times, suggested that the nucleus of the hydrogen atom is included in the nucleus of the atom of any element. Somewhat later, Rutherford conducted an experiment in which he studied the interaction of the nuclei of a nitrogen atom with alpha particles. As a result of the experiment, a particle flew out from the nucleus of the atom, which Rutherford called “proton” (from the Greek word “protos” - first) and assumed that it was the nucleus of the hydrogen atom. The assumption was proven experimentally by repeating this scientific experiment in a cloud chamber.

The same Rutherford in 1920 put forward a hypothesis about the existence in the atomic nucleus of a particle whose mass is equal to the mass of a proton, but does not carry any electric charge. However, Rutherford himself failed to detect this particle. But in 1932, his student Chadwick experimentally proved the existence of a neutron in the atomic nucleus - a particle, as predicted by Rutherford, approximately equal in mass to a proton. Neutrons were more difficult to detect because they have no electrical charge and, accordingly, do not interact with other nuclei. The absence of charge explains the very high penetrating ability of neutrons.

Protons and neutrons are bound together in the atomic nucleus by a very strong force. Now physicists agree that these two elementary nuclear particles are very similar to each other. So, they have equal spins, and nuclear forces act on them absolutely equally. The only difference is that the proton has a positive charge, while the neutron has no charge at all. But since the electric charge has no meaning in nuclear interactions, it can only be considered as a kind of mark of the proton. If you deprive a proton of an electric charge, it will lose its individuality.