What is a positive charge in physics definition. The minimum electric charge - the charge of an electron is

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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 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 electrization

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 are 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.

An electron is an elementary particle, which is one of the main units in the structure of matter. The charge of an electron is negative. The most accurate measurements were made in the early twentieth century by Millikan and Ioffe.

The electron charge is equal to minus 1.602176487 (40) * 10 -1 9 C.

Through this value, the electric charge of other smallest particles is measured.

General concept of the electron

In particle physics, it is said that the electron is indivisible and has no structure. It is involved in electromagnetic and gravitational processes, belongs to the lepton group, just like its antiparticle, the positron. Among other leptons, it has the lightest weight. If electrons and positrons collide, this leads to their annihilation. Such a pair can arise from the gamma-quantum of particles.

Before the neutrino was measured, it was the electron that was considered the lightest particle. In quantum mechanics, it is referred to as fermions. The electron also has a magnetic moment. If a positron is also referred to it, then the positron is separated as a positively charged particle, and the electron is called a negatron, as a particle with a negative charge.

Individual properties of electrons

Electrons belong to the first generation of leptons, with the properties of particles and waves. Each of them is endowed with a quantum state, which is determined by measuring the energy, spin orientation, and other parameters. He reveals his belonging to fermions through the impossibility of having two electrons in the same quantum state at the same time (according to the Pauli principle).

It is studied in the same way as a quasiparticle in a periodic crystal potential, in which the effective mass can differ significantly from the mass at rest.

Through the movement of electrons, an electric current, magnetism and thermo EMF occur. The charge of an electron in motion forms a magnetic field. However, an external magnetic field deflects the particle from a straight direction. When accelerated, the electron acquires the ability to absorb or emit energy as a photon. Its set consists of electron atomic shells, the number and position of which determine the chemical properties.

The atomic mass mainly consists of nuclear protons and neutrons, while the mass of electrons is about 0.06% of the total atomic weight. The Coulomb electric force is one of the main forces that can keep an electron close to the nucleus. But when molecules are created from atoms and chemical bonds arise, electrons are redistributed in the new space formed.

Nucleons and hadrons are involved in the appearance of electrons. Isotopes with radioactive properties are capable of emitting electrons. Under laboratory conditions, these particles can be studied in special instruments, and, for example, telescopes can detect radiation from them in plasma clouds.

Opening

The electron was discovered by German physicists in the nineteenth century, when they studied the cathodic properties of rays. Then other scientists began to study it in more detail, bringing it to the rank of a separate particle. Radiation and other related physical phenomena were studied.

For example, a group led by Thomson estimated the charge of an electron and the mass of cathode rays, the ratios of which, as they found out, do not depend on a material source.
And Becquerel found that minerals emit radiation by themselves, and their beta rays can be deflected by the action of an electric field, while the mass and charge retained the same ratio as the cathode rays.

Atomic theory

According to this theory, an atom consists of a nucleus and electrons around it, arranged in the form of a cloud. They are in some quantized states of energy, the change of which is accompanied by the process of absorption or emission of photons.

Quantum mechanics

At the beginning of the twentieth century, a hypothesis was formulated according to which material particles have the properties of both proper particles and waves. Also, light can manifest itself in the form of a wave (it is called the de Broglie wave) and particles (photons).

As a result, the famous Schrödinger equation was formulated, which described the propagation of electron waves. This approach is called quantum mechanics. It was used to calculate the electronic states of energy in the hydrogen atom.

Fundamental and quantum properties of the electron

The particle exhibits fundamental and quantum properties.

The fundamental ones include mass (9.109 * 10 -31 kilograms), elementary electric charge (that is, the minimum portion of the charge). According to the measurements that have been carried out so far, no elements are found in the electron that can reveal its substructure. But some scientists are of the opinion that it is a point charged particle. As indicated at the beginning of the article, the electronic electric charge is -1.602 * 10 -19 C.

Being a particle, an electron can simultaneously be a wave. The experiment with two slits confirms the possibility of its simultaneous passage through both of them. This conflicts with the properties of the particle, where it is only possible to pass through one slit each time.

Electrons are considered to have the same physical properties. Therefore, their permutation, from the point of view of quantum mechanics, does not lead to a change in the system state. The wave function of electrons is antisymmetric. Therefore, its solutions vanish when identical electrons enter the same quantum state (Pauli's principle).

Any electric charge observed in an experiment is always a multiple of one elementary charge.- such an assumption was made by B. Franklin in 1752 and subsequently repeatedly tested experimentally. The elementary charge was first experimentally measured by Millikan in 1910.

The fact that electric charge occurs in nature only in the form of an integer number of elementary charges can be called quantization of electric charge. At the same time, in classical electrodynamics, the question of the causes of charge quantization is not discussed, since the charge is an external parameter, and not a dynamic variable. A satisfactory explanation for why the charge must be quantized has not yet been found, but a number of interesting observations have already been obtained.

Fractional electric charge

Repeated searches for long-lived free objects with a fractional electric charge, carried out by various methods for a long time, have not yielded results.

However, it should be noted that the electric charge of quasiparticles may also not be a multiple of the whole. In particular, it is quasiparticles with a fractional electric charge that are responsible for the fractional quantum Hall effect.

Experimental definition of elementary electric charge

Avogadro's number and Faraday's constant

Josephson effect and von Klitzing constant

Another precise method for measuring the elementary charge is to calculate it from the observation of two effects of quantum mechanics: the Josephson effect, in which voltage fluctuations occur in a certain superconducting structure, and the quantum Hall effect, the effect of quantization of the Hall resistance or conductivity of a two-dimensional electron gas in strong magnetic fields and at low temperatures . Josephson constant

Where h- Planck's constant, can be measured directly using the Josephson effect.

can be measured directly using the quantum Hall effect.

From these two constants, the magnitude of the elementary charge can be calculated:

see also

Notes

1. elementary charge(English) . The NIST Reference on Constants, Units, and Uncertainty. . Retrieved May 20, 2016.
2. The value in CGSE units is given as the result of converting the value of CODATA in coulombs, taking into account the fact that the coulomb is exactly equal to 2,997,924,580 CGSE electric charge units (franklins or statcoulombs).
3. Tomilin K. A. Fundamental physical constants in historical and methodological aspects. - M. : Fizmatlit, 2006. - S. 96-105. - 368 p. - 400 copies. - ISBN 5-9221-0728-3.
4. A topological model of composite preons (unavailable link) es.arXiv.org
5. V.M. Abazov et al.(DØ Collaboration) (2007). “Experimental discrimination between charge 2 e/3 top quark and charge 4 e/3 exotic quark production scenarios”. Physical Review Letters. 98 (4): 041801.

Like the concept of the gravitational mass of a body in Newtonian mechanics, the concept of charge in electrodynamics is the primary, basic concept.

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

Electric charge is usually denoted by the letters q or Q.

The totality of all known experimental facts allows us to draw the following conclusions:

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

Charges can be transferred (for example, by direct contact) from one body to another. Unlike body mass, electric charge is not an inherent characteristic of a given body. The same body in different conditions can have a different charge.

Like charges repel, unlike charges attract. This also shows the fundamental difference between electromagnetic forces and gravitational ones. Gravitational forces are always forces of attraction.

One of the fundamental laws of nature is the experimentally established law of conservation of electric charge .

In an isolated system, the algebraic sum of the charges of all bodies remains constant:

The law of conservation of electric charge states that in a closed system of bodies processes of the birth or disappearance of charges of only one sign cannot be observed.

From the modern point of view, charge carriers are elementary particles. All ordinary 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. The electric charges of the proton and electron modulo are exactly the same and equal to the elementary charge e.

In a neutral atom, the number of protons in the nucleus is equal to the number of electrons in the shell. This number is called atomic number . An atom of a given substance can lose one or more electrons or gain an extra electron. In these cases, the neutral atom turns into a positively or negatively charged ion.

A charge can be transferred from one body to another only in portions containing an integer number of elementary charges. Thus, the electric charge of the body is a discrete quantity:

Physical quantities that can only take on a discrete series of values ​​are called quantized . elementary charge e is a quantum (smallest portion) of electric charge. It should be noted that in modern elementary particle physics, the existence of so-called quarks is assumed - particles with a fractional charge and However, quarks in the free state have not yet been observed.

In conventional laboratory experiments, electric charges are detected and measured using electrometer ( or electroscope) - a device consisting of a metal rod and an arrow that can rotate around a horizontal axis (Fig. 1.1.1). The arrowhead is insulated from the metal case. When a charged body comes into contact with the rod of an electrometer, electric charges of the same sign are distributed along the rod and the arrow. The forces of electrical repulsion cause the arrow to turn at a certain angle, by which one can judge the charge transferred to the rod of the electrometer.

The electrometer is a fairly crude instrument; it does not allow one to investigate the forces of interaction of charges. For the first time, the law of interaction of fixed charges was discovered by the French physicist Charles Coulomb in 1785. In his experiments, Coulomb measured the forces of attraction and repulsion of charged balls using a device he designed - a torsion balance (Fig. 1.1.2), which was distinguished by extremely high sensitivity. So, for example, the balance beam was rotated by 1 ° under the action of a force of the order of 10 -9 N.

The idea of ​​measurements was based on Coulomb's brilliant guess that if a charged ball is brought into contact with exactly the same uncharged one, then the charge of the first will be divided equally between them. Thus, a method was indicated to change the charge of the ball by two, three, etc. times. Coulomb's experiments measured the interaction between balls whose dimensions are much smaller than the distance between them. Such charged bodies are called point charges.

point charge called a charged body, the dimensions of which can be neglected under the conditions of this problem.

Based on numerous experiments, Coulomb established the following law:

The forces of interaction of fixed charges are directly proportional to the product of charge modules and inversely proportional to the square of the distance between them:

Interaction forces obey Newton's third law:

They are repulsive forces with the same signs of charges and attractive forces with different signs (Fig. 1.1.3). The interaction of fixed electric charges is called electrostatic or Coulomb interaction. The section of electrodynamics that studies the Coulomb interaction is called electrostatics .

Coulomb's law is valid for point charged bodies. In practice, Coulomb's law is well satisfied if the dimensions of the charged bodies are much smaller than the distance between them.

Proportionality factor k in Coulomb's law depends on the choice of the system of units. In the International SI system, the unit of charge is pendant(Cl).

Pendant - this is the charge passing in 1 s through the cross section of the conductor at a current strength of 1 A. The unit of current strength (Ampere) in SI is, along with units of length, time and mass basic unit of measure.

Coefficient k in the SI system is usually written as:

Where - electrical constant .

In the SI system, the elementary charge e equals:

Experience shows that the Coulomb interaction forces obey the superposition principle:

If a charged body interacts simultaneously with several charged bodies, then the resulting force acting on this body is equal to the vector sum of the forces acting on this body from all other charged bodies.

Rice. 1.1.4 explains the principle of superposition using the example of the electrostatic interaction of three charged bodies.

The principle of superposition is a fundamental law of nature. However, its use requires some caution when it comes to the interaction of charged bodies of finite size (for example, two conductive charged balls 1 and 2). If a third charged ball is raised to a system of two charged balls, then the interaction between 1 and 2 will change due to charge redistribution.

The principle of superposition states that when given (fixed) charge distribution on all bodies, the forces of electrostatic interaction between any two bodies do not depend on the presence of other charged bodies.

elementary electric charge elementary electric charge

(e), the minimum electric charge, positive or negative, whose magnitude e≈4.8 10 -10 CGSE units, or 1.6 10 -19 C. Almost all charged elementary particles have a charge + e or - e(an exception is some resonances with a charge that is a multiple of e); particles with fractional electric charges have not been observed, however, in the modern theory of strong interaction - quantum chromodynamics - the existence of quarks is assumed - particles with charges that are multiples of 1 / 3 e.

ELEMENTARY ELECTRIC CHARGE ( e), the minimum electric charge, positive or negative, equal to the charge of an electron.
The assumption that any electric charge observed in the experiment is always a multiple of the elementary charge was made by B. Franklin (cm. FRANKLIN Benjamin) in 1752 Thanks to the experiments of M. Faraday (cm. FARADEUS Michael) by electrolysis, the value of the elementary charge was calculated in 1834. The existence of an elementary electric charge was also pointed out in 1874 by the English scientist J. Stoney. He also introduced the concept of "electron" into physics and proposed a method for calculating the value of an elementary charge. For the first time experimentally elementary electric charge was measured by R. Milliken (cm. MILLIKEN Robert Andrus) in 1908
Material carriers of an elementary electric charge in nature are charged elementary particles (cm. ELEMENTARY PARTICLES).
Electric charge (cm. ELECTRIC CHARGE) of any microsystem and macroscopic bodies is always equal to the algebraic sum of the elementary charges included in the system, that is, an integer multiple of the value of e (or zero).
The currently established value of the absolute value of the elementary electric charge (cm. ELEMENTARY ELECTRIC CHARGE) is e = (4.8032068 0.0000015) . 10 -10 CGSE units, or 1.60217733 . 10 -19 C. The value of the elementary electric charge calculated by the formula, expressed in terms of physical constants, gives the value for the elementary electric charge: e = 4.80320419(21) . 10 -10 , or: e \u003d 1.602176462 (65) . 10 -19 C.
It is believed that this charge is really elementary, that is, it cannot be divided into parts, and the charges of any objects are its integer multiples. The electric charge of an elementary particle is its fundamental characteristic and does not depend on the choice of reference system. The elementary electric charge is exactly equal to the electric charge of the electron, proton and almost all other charged elementary particles, which are thus the material carriers of the smallest charge in nature.
There is a positive and negative elementary electric charge, and the elementary particle and its antiparticle have charges of opposite signs. The carrier of an elementary negative charge is an electron, the mass of which is me = 9.11. 10 -31 kg. The carrier of the elementary positive charge is the proton, whose mass is mp = 1.67. 10 -27 kg.
The fact that electric charge occurs in nature only in the form of an integer number of elementary charges can be called the quantization of electric charge. Almost all charged elementary particles have a charge e - or e + (an exception is some resonances with a charge that is a multiple of e); particles with fractional electric charges have not been observed, however, in the modern theory of strong interaction - quantum chromodynamics - the existence of particles - quarks - with charges that are multiples of 1/3 e.
An elementary electrical charge cannot be destroyed; this fact is the content of the law of conservation of electric charge at the microscopic level. Electric charges can disappear and reappear. However, two elementary charges of opposite signs always appear or disappear.
The value of an elementary electric charge is a constant of electromagnetic interactions and is included in all equations of microscopic electrodynamics.