What is an elementary charge. elementary electric charge

The German physicist and physiologist G. Helmholtz drew attention to the fact that the charges carried by ions during the phenomenon of electrolysis are integer multiples of some value equal to C. Each monovalent ion carries such a charge. Any divalent ion carries a charge equal to Cl, and so on. Helmholtz concluded that the charge C is the minimum amount of electricity that exists in nature. This charge is called the elementary charge. So, for example, anions of chlorine, iodine carry one negative elementary charge, and monovalent cations, for example, hydrogen, potassium, have one positive elementary charge.

In the phenomena associated with electrolysis, scientists first discovered the discreteness of electricity and were able to determine the magnitude of the elementary charge.

Somewhat later, the Irishman D. Stoney spoke about the existence of an elementary charge inside the atom. He proposed to call this elementary charge an electron. The charge of an electron is often denoted by e or .

When charging a body, we create on it an excess of electrons or a deficiency in comparison with their normal amount, in which the body has no charge. In this case, electrons are taken from another body or removed from the charged body, but are not destroyed or created. It is important to remember that the process of charging and discharging bodies is a procedure for the redistribution of electrons, while their total number does not change.

When a charged conductor is connected to an uncharged one, the charge is redistributed between both bodies. Suppose that one body carries a negative charge, it is connected to an uncharged body. The electrons of a charged body under the influence of mutual repulsion forces pass to an uncharged body. In this case, the charge of the first body decreases, the charge of the second increases, until equilibrium is reached.

If positive and negative charges are connected, they cancel each other out. This means that by combining negative and positive charges of the same magnitude, we get an uncharged body.

When electrifying bodies, using friction, the redistribution of charges also occurs. The main reason for this is the transfer of part of the electrons during close contact of bodies from one body to another.

Experiments by Millikan and Ioffe proving the existence of the electron

Empirically, the existence of an elementary charge carried by an electron was proved by the American scientist R. Milliken. He measured the speed of oil droplets in a uniform electric field between two electric plates. The drop was charging. The scientist compared the speed of movement of a drop without a charge and the same drop with a charge. By measuring the field strength between the plates, the charge of the drop was found.

A.F. Ioffe conducted similar experiments, but at the same time used metal dust particles as objects of study. By changing the field strength between the plates, Ioffe obtained the equality of the force of gravity and the Coulomb force, while the dust particle remained motionless. When a dust particle was illuminated with ultraviolet light, its charge was changed. To compensate for gravity, the field strength was changed. So the scientist received the value by which the charge of the dust particle changed.

It has been empirically shown that the charges of dust grains and drops always change abruptly. The minimum charge change turned out to be:

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

An elementary electric charge is a fundamental physical constant, the minimum portion (quantum) of an electric charge. Equals approximately

e=1.602 176 565 (35) 10 −19 C

in the International System of Units (SI). Closely related to the fine structure constant, which describes the electromagnetic interaction.

"Any electric charge observed in an experiment is always a multiple of the 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 the 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.

• · If a magnetic monopole exists in nature, then, according to quantum mechanics, its magnetic charge must be in a certain ratio with the charge of any chosen elementary particle. It automatically follows from this that the mere existence of a magnetic monopole entails charge quantization. However, it was not possible to detect a magnetic monopole in nature.
• · In modern elementary particle physics, other models are being developed in which all known fundamental particles would turn out to be simple combinations of new, even more fundamental particles. In this case, the quantization of the charge of the observed particles does not seem surprising, since it arises "by construction".

It is also possible that all the parameters of the observed particles will be described within the framework of a unified field theory, approaches to which are currently being developed. In such theories, the magnitude of the electric charge of the particles must be calculated from an extremely small number of fundamental parameters, possibly related to the structure of space-time at ultrasmall distances. If such a theory is constructed, then what we observe as an elementary electric charge will turn out to be some discrete space-time invariant. Such an approach is developed, for example, in the S. Bilson-Thompson model, in which the fermions of the standard model are interpreted as three ribbons of space-time braided into a braid, and the electric charge (more precisely, a third of it) corresponds to a ribbon twisted by 180°. However, despite the elegance of such models, specific generally accepted results in this direction have not yet been obtained.

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.

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).

Electric charge- a physical quantity characterizing the ability of bodies to enter into electromagnetic interactions. Measured in Coulomb.

elementary electric charge- the minimum charge that elementary particles have (the charge of a proton and an electron).

The body has a charge, means it has extra or missing electrons. This charge is denoted q=ne. (it is equal to the number of elementary charges).

electrify the body- to create an excess and a shortage of electrons. Ways: electrification by friction And electrification by contact.

pinpoint dawn e - the charge of the body, which can be taken as a material point.

trial charge() - a point, small charge, necessarily positive - is used to study the electric field.

Law of conservation of charge:in an isolated system, the algebraic sum of the charges of all bodies remains constant for any interactions of these bodies with each other.

Coulomb's Law:the interaction forces of two point charges are proportional to the product of these charges, inversely proportional to the square of the distance between them, depend on the properties of the medium and are directed along the straight line connecting their centers.

, Where
F / m, C 2 / nm 2 - dielectric. fast. vacuum

- relates. dielectric constant (>1)

- absolute dielectric permeability. environments

Electric field- the material medium through which the interaction of electric charges occurs.

Electric field properties:

Characteristics of the electric field:

tension(E) is a vector quantity equal to the force acting on a unit test charge placed at a given point.

Measured in N/C.

Direction is the same as for the active force.

tension does not depend neither on strength nor on the magnitude of the trial charge.

Superposition of electric fields: the strength of the field created by several charges is equal to the vector sum of the field strengths of each charge:

Graphically The electronic field is depicted using lines of tension.

tension line- a line, the tangent to which at each point coincides with the direction of the tension vector.

Stress Line Properties: they do not intersect, only one line can be drawn through each point; they are not closed, leave a positive charge and enter a negative one, or dissipate to infinity.

Field types:

Uniform electric field- a field, the intensity vector of which at each point is the same in absolute value and direction.

Non-uniform electric field- a field, the intensity vector of which at each point is not the same in absolute value and direction.

Constant electric field– the tension vector does not change.

Non-constant electric field- the tension vector changes.

The work of the electric field to move the charge.

, where F is force, S is displacement, - angle between F and S.

For a uniform field: the force is constant.

The work does not depend on the shape of the trajectory; the work done to move along a closed path is zero.

For an inhomogeneous field:

Electric field potential- the ratio of the work that the field does, moving the trial electric charge to infinity, to the magnitude of this charge.

-potential is the energy characteristic of the field. Measured in Volts

Potential difference:

If
, That

, Means

-potential gradient.

For a homogeneous field: potential difference - voltage:

. It is measured in Volts, devices - voltmeters.

Electrical capacity- the ability of bodies to accumulate an electric charge; the ratio of charge to potential, which is always constant for a given conductor.

.

Does not depend on charge and does not depend on potential. But it depends on the size and shape of the conductor; on the dielectric properties of the medium.

, where r is the size,
- permeability of the medium around the body.

The electrical capacity increases if any bodies are nearby - conductors or dielectrics.

Capacitor- a device for accumulating a charge. Electrical capacity:

Flat capacitor- two metal plates with a dielectric between them. Capacitance of a flat capacitor:

, where S is the area of ​​the plates, d is the distance between the plates.

Energy of a charged capacitor is equal to the work done by the electric field in transferring charge from one plate to another.

Small charge transfer
, the voltage will change to
, work will be done
. Because
, and C \u003d const,
. Then
. We integrate:

Electric field energy:
, where V=Sl is the volume occupied by the electric field

For an inhomogeneous field:
.

Volumetric electric field density:
. Measured in J / m 3.

electric dipole- a system consisting of two equal, but opposite in sign, point electric charges located at some distance from each other (dipole arm -l).

The main characteristic of a dipole is dipole moment is a vector equal to the product of the charge and the arm of the dipole, directed from a negative charge to a positive one. Denoted
. Measured in coulomb meters.

Dipole in a uniform electric field.

The forces acting on each of the charges of the dipole are:
And
. These forces are oppositely directed and create a moment of a pair of forces - torque:, where

M - torque F - forces acting on the dipole

d– arm arm l– arm of the dipole

p– dipole moment E– intensity

- angle between p Eq - charge

Under the action of a torque, the dipole will turn and settle in the direction of the lines of tension. The vectors pi and E will be parallel and unidirectional.

Dipole in an inhomogeneous electric field.

There is a torque, so the dipole will turn. But the forces will be unequal, and the dipole will move to where the force is greater.

-tension gradient. The higher the tension gradient, the higher the lateral force that pulls the dipole off. The dipole is oriented along the lines of force.

Dipole's own field.

But . Then:

.

Let the dipole be at point O and its arm be small. Then:

.

The formula was obtained taking into account:

Thus, the potential difference depends on the sine of the half-angle at which the dipole points are visible, and the projection of the dipole moment onto the straight line connecting these points.

Dielectrics in an electric field.

Dielectric A substance that has no free charges and therefore does not conduct electricity. However, in fact, conductivity exists, but it is negligible.

Dielectric classes:

with polar molecules (water, nitrobenzene): the molecules are not symmetrical, the centers of mass of positive and negative charges do not coincide, which means that they have a dipole moment even in the case when there is no electric field.

with non-polar molecules (hydrogen, oxygen): the molecules are symmetrical, the centers of mass of positive and negative charges coincide, which means that they do not have a dipole moment in the absence of an electric field.

crystalline (sodium chloride): a combination of two sublattices, one of which is positively charged and the other is negatively charged; in the absence of an electric field, the total dipole moment is zero.

Polarization- the process of spatial separation of charges, the appearance of bound charges on the surface of the dielectric, which leads to a weakening of the field inside the dielectric.

Polarization ways:

1 way - electrochemical polarization:

On the electrodes - the movement of cations and anions towards them, the neutralization of substances; areas of positive and negative charges are formed. The current gradually decreases. The rate of establishment of the neutralization mechanism is characterized by the relaxation time - this is the time during which the polarization EMF will increase from 0 to the maximum from the moment the field is applied. = 10 -3 -10 -2 s.

Method 2 - orientational polarization:

On the surface of the dielectric, uncompensated polar ones are formed, i.e. polarization occurs. The tension inside the dielectric is less than the external tension. Relaxation time: = 10 -13 -10 -7 s. Frequency 10 MHz.

3 way - electronic polarization:

Characteristic of non-polar molecules that become dipoles. Relaxation time: = 10 -16 -10 -14 s. Frequency 10 8 MHz.

4 way - ionic polarization:

Two lattices (Na and Cl) are displaced relative to each other.

Relaxation time:

Method 5 - microstructural polarization:

It is typical for biological structures when charged and uncharged layers alternate. There is a redistribution of ions on semi-permeable or ion-impermeable partitions.

Relaxation time: \u003d 10 -8 -10 -3 s. Frequency 1 kHz

Numerical characteristics of the degree of polarization:

Electricity is the ordered movement of free charges in matter or in vacuum.

Conditions for the existence of an electric current:

presence of free charges

the presence of an electric field, i.e. forces acting on these charges

Current strength- a value equal to the charge that passes through any cross section of the conductor per unit time (1 second)

Measured in amperes.

n is the concentration of charges

q is the amount of charge

S- cross-sectional area of ​​the conductor

- speed of the directed movement of particles.

The speed of movement of charged particles in an electric field is small - 7 * 10 -5 m / s, the speed of propagation of the electric field is 3 * 10 8 m / s.

current density- the amount of charge passing in 1 second through a section of 1 m 2.

. Measured in A / m 2.

- the force acting on the ion from the side of the electric field is equal to the friction force

- ion mobility

- speed of directed movement of ions = mobility, field strength

The specific conductivity of the electrolyte is the greater, the greater the concentration of ions, their charge and mobility. As the temperature rises, the mobility of the ions increases and the electrical conductivity increases.