Electric charge– a physical quantity characterizing the ability of bodies to enter into electromagnetic interactions. Measured in Coulombs.
Elementary electric charge– the minimum charge that elementary particles have (proton and electron charge).
e= Cl
The body has a charge, means it has extra or missing electrons. This charge is designated q = ne. (it is equal to the number of elementary charges).
Electrify the body– create an excess and deficiency of electrons. Methods: electrification by friction And electrification by contact.
Point dawn d is the charge of the body, which can be taken as a material point.
Test charge (
) – point, small charge, always positive – 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 forces of interaction between 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, Cl 2 /nm 2 – dielectric. fast. vacuum
- relates. dielectric constant (>1)
- absolute dielectric permeability. environment
Electric field– a material medium through which the interaction of electric charges occurs.
Electric field properties:
Electric field characteristics:
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– the same as that of the acting force.
Tension does not depend neither on the strength nor on the size of the test charge.
Superposition of electric fields: the field strength created by several charges is equal to the vector sum of the field strengths of each charge:
Graphically The electronic field is represented using tension lines.
Tension line– a line whose tangent at each point coincides with the direction of the tension vector.
Properties of tension lines: they do not intersect, only one line can be drawn through each point; they are not closed, they leave a positive charge and enter a negative one, or dissipate into infinity.
Types of fields:
Uniform electric field– a field whose intensity vector at each point is the same in magnitude and direction.
Non-uniform electric field– a field whose intensity vector at each point is unequal in magnitude and direction.
Constant electric field– the tension vector does not change.
Variable electric field– the tension vector changes.
Work done by an electric field to move a 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 a non-uniform field:
Electric field potential– the ratio of the work that the field does, moving a test electric charge to infinity, to the magnitude of this charge.
- potential– energy characteristic of the field. Measured in Volts
Potential difference:
If 
, That 
, Means 
- potential gradient.
For a uniform field: potential difference – voltage:
. It is measured in Volts, the devices are voltmeters.
Electrical capacity– the ability of bodies to accumulate electrical 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 environment around the body.
Electrical capacity increases if any bodies - conductors or dielectrics - are nearby.
Capacitor– device for accumulating charge. Electrical capacity: 
Flat capacitor– two metal plates with a dielectric between them. Electric capacity of a flat capacitor:
, where S is the area of the plates, d is the distance between the plates.
Energy of a charged capacitor equal to the work done by the electric field when transferring charge from one plate to another.
Small charge transfer 
, the voltage will change to 
, the work is done 
. Because 
, and C = const, 
. Then 
. Let's integrate:
Electric field energy:
, where V=Sl is the volume occupied by the electric field
For a non-uniform 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– a vector equal to the product of the charge and the dipole arm, directed from the negative charge to the positive one. Designated 
. Measured in Coulomb meters.
Dipole in a uniform electric field.
The following forces act on each charge of the dipole: 
And 
. These forces are oppositely directed and create a moment of a pair of forces - a torque: , where
M – torque F – forces acting on the dipole
d – force arm l – dipole arm
p – dipole moment E – tension
- angle between p and E q – charge
Under the influence of a torque, the dipole will rotate and align itself in the direction of the tension lines. Vectors p and E will be parallel and unidirectional.
Dipole in a non-uniform electric field.
There is a torque, which means the dipole will rotate. 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. The dipole is oriented along the lines of force.
Dipole intrinsic field.
But . Then:
.
Let the dipole be at point O and its arm 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 does not have free charges, and therefore does not conduct electric current. 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 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 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 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 methods:
Method 1 – electrochemical polarization:
On the electrodes – movement of cations and anions towards them, 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 increases from 0 to a maximum from the moment the field is applied. 
= 10 -3 -10 -2 s.
Method 2 – orientational polarization:
Uncompensated polar ones are formed on the surface of the dielectric, i.e. the phenomenon of polarization occurs. The voltage inside the dielectric is less than the external voltage. Relaxation time: 
= 10 -13 -10 -7 s. Frequency 10 MHz.
Method 3 – electronic polarization:
Characteristic of non-polar molecules that become dipoles. Relaxation time: 
= 10 -16 -10 -14 s. Frequency 10 8 MHz.
Method 4 – ion polarization:
Two lattices (Na and Cl) are displaced relative to each other.
Relaxation time: 
Method 5 – microstructural polarization:
Characteristic of biological structures when charged and uncharged layers alternate. There is a redistribution of ions on semi-permeable or ion-impermeable partitions.
Relaxation time: 
=10 -8 -10 -3 s. Frequency 1KHz
Numerical characteristics of the degree of polarization:
Electricity– this is the ordered movement of free charges in matter or in a vacuum.
Conditions for the existence of 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 a conductor per unit of time (1 second)
Measured in Amperes.
n – charge concentration
q – charge amount
S – cross-sectional area of the conductor
- speed of directional 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 through a cross section of 1 m2 in 1 second.
. Measured in A/m2.
- the force acting on the ion from the electric field is equal to the friction force
- ion mobility
- speed of directional movement of ions = mobility, field strength
The greater the concentration of ions, their charge and mobility, the greater the specific conductivity of the electrolyte. As the temperature increases, the mobility of ions increases and the electrical conductivity increases.
| Electric charge | |
|---|---|
| q, Q | |
| Dimension | T I |
| Units | |
| SI | pendant |
| SSSE | statcoulon (Franklin) |
| SGSM | abculon |
| Other units | ampere-hour, faraday, elementary charge |
| Notes | |
| scalar quantity, quantized | |
Electrostatics
Electrostatics called a section of the study of electricity, in which the interactions and properties of systems of electric charges stationary relative to a selected inertial reference frame are studied.
The amount of electric charge (in other words, just electric charge) can take on both positive and negative values; it is a numerical characteristic of charge carriers and charged bodies. This value is determined in such a way that the force interaction transferred by the field between charges is directly proportional to the size of the charges, particles or bodies interacting with each other, and the directions of the forces acting on them from the electromagnetic field depend on the sign of the charges.
The electric charge of any system of bodies consists of an integer number of elementary charges equal to approximately 1.6⋅10 −19 C in the SI system or 4.8⋅10 −10 units. SGSE. Electric charge carriers are electrically charged elementary particles. The smallest particle by mass that is stable in a free state and has one negative elementary electric charge is the electron (its mass is 9.11⋅10 −31 kg). The smallest antiparticle stable in a free state with a positive elementary charge is a positron, which has the same mass as an electron. There is also a stable particle with one positive elementary charge - a proton (mass equal to 1.67⋅10 −27 kg) and other, less common particles. It was hypothesized (1964) that there are also particles with a smaller charge (±⅓ and ±⅔ elementary charge) - quarks; however, they are not isolated in a free state (and, apparently, can only exist as part of other particles - hadrons), as a result, any free particle carries only an integer number of elementary charges.
The electric charge of any elementary particle is a relativistically invariant quantity. It does not depend on the reference system, which means it does not depend on whether this charge is moving or at rest; it is inherent in this particle throughout its entire life, therefore elementary charged particles are often identified with their electric charges. In general, there are as many negative charges in nature as positive ones. The electric charges of atoms and molecules are equal to zero, and the charges of positive and negative ions in each cell of the crystal lattices of solids are compensated.
Charge interaction
The simplest and most everyday phenomenon in which the fact of the existence of electric charges in nature is revealed is the electrification of bodies upon contact. The ability of electric charges to both attract and repel each other is explained by the existence of two different types of charges. One type of electric charge is called positive, and the other - negative. Oppositely charged bodies attract, and similarly charged bodies repel each other.
When two electrically neutral bodies come into contact as a result of friction, charges are transferred from one body to another. In each of them, the equality of the sum of positive and negative charges is violated, and the bodies are charged differently.
When a body is electrified through influence, the uniform distribution of charges in it is disrupted. They are redistributed so that an excess of positive charges appears in one part of the body, and negative charges in another. If these two parts are separated, they will be charged oppositely.
| Symmetry in physics | ||
|---|---|---|
| Conversion | Corresponding invariance |
Corresponding law conservation |
| ↕ Time broadcasts | Uniformity time |
...energy |
| ⊠ , , and -symmetries | Isotropy time |
...evenness |
| ↔ Broadcast space | Uniformity space |
...impulse |
| ↺ Rotations of space | Isotropy space |
...of the moment impulse |
| ⇆ Lorentz group (boosts) | Relativity Lorentz covariance |
...movements center of mass |
| ~ Gauge transformation | Gauge invariance | ...charge |
Law of conservation of electric charge
The electric charge of a closed system is conserved in time and is quantized - it changes in portions that are multiples of the elementary electric charge, that is, in other words, the algebraic sum of the electric charges of bodies or particles forming an electrically isolated system does not change during any processes occurring in this system.
In the system under consideration, new electrically charged particles can be formed, for example, electrons - due to the phenomenon of ionization of atoms or molecules, ions - due to the phenomenon of electrolytic dissociation, etc. However, if the system is electrically isolated, then the algebraic sum of the charges of all particles, including again appeared in such a system is always preserved.
Simple experiments on the electrification of various bodies illustrate the following points.
1. There are two types of charges: positive (+) and negative (-). A positive charge occurs when glass rubs against leather or silk, and a negative charge occurs when amber (or ebonite) rubs against wool.
2. Charges (or charged bodies) interact with each other. Same charges push away, and unlike charges are attracted.
3. The state of electrification can be transferred from one body to another, which is associated with the transfer of electric charge. In this case, a larger or smaller charge can be transferred to the body, i.e. the charge has a magnitude. When electrified by friction, both bodies acquire a charge, one being positive and the other negative. It should be emphasized that the absolute values of the charges of bodies electrified by friction are equal, which is confirmed by numerous measurements of charges using electrometers.
It became possible to explain why bodies become electrified (i.e., charged) during friction after the discovery of the electron and the study of the structure of the atom. As you know, all substances consist of atoms; atoms, in turn, consist of elementary particles - negatively charged electrons, positively charged protons and neutral particles - neutrons. Electrons and protons are carriers of elementary (minimal) electrical charges.
Elementary electric charge ( e) is the smallest electric charge, positive or negative, equal to the electron charge:
e = 1.6021892(46) 10 -19 C.
There are many charged elementary particles, and almost all of them have a charge +e or -e, however, these particles are very short-lived. They live less than a millionth of a second. Only electrons and protons exist in a free state indefinitely.
Protons and neutrons (nucleons) make up the positively charged nucleus of an atom, around which negatively charged electrons rotate, the number of which is equal to the number of protons, so that the atom as a whole is a powerhouse.
Under normal conditions, bodies consisting of atoms (or molecules) are electrically neutral. However, during the process of friction, some of the electrons that have left their atoms can move from one body to another. The electron movements do not exceed the interatomic distances. But if the bodies are separated after friction, they will turn out to be charged; the body that gave up some of its electrons will be charged positively, and the body that acquired them will be negatively charged.
So, bodies become electrified, that is, they receive an electric charge when they lose or gain electrons. In some cases, electrification is caused by the movement of ions. In this case, no new electrical charges arise. There is only a division of the existing charges between the electrifying bodies: part of the negative charges passes from one body to another.
Determination of charge.
It should be especially emphasized that charge is an integral property of the particle. You can imagine a particle without a charge, but you cannot imagine a charge without a particle.
Charged particles manifest themselves in attraction (opposite charges) or repulsion (like charges) with forces that are many orders of magnitude greater than gravitational forces. Thus, the force of electrical attraction of an electron to the nucleus in a hydrogen atom is 10 39 times greater than the force of gravitational attraction of these particles. The interaction between charged particles is called electromagnetic interaction, and the electric charge determines the intensity of electromagnetic interactions.
In modern physics, charge is defined as follows:
Electric charge is a physical quantity that is the source of the electric field through which the interaction of particles with a charge occurs.
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 encounter 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 the forces of universal gravity.
Electric charge is a physical quantity that 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. Good conductors are all metals (conductors of the first kind), aqueous solutions of 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.
A unit of measurement for electrical charge. Pendant. Relationship with other physical quantities. (10+)
A unit of measurement for electrical charge. Pendant (Coulomb)
The material is an explanation and addition to the article:
Units of measurement of physical quantities in radio electronics
Units of measurement and relationships of physical quantities used in radio engineering.
The electric charge of a body is the difference between the number of charged particles of one polarity and another polarity located in this body (with some assumptions). Electric charge can have positive or negative polarity. Bodies with a charge of the same polarity repel, and bodies of different polarity attract.
Electric charge is measured in Coulombs. Designation K. International designation C. Charge in formulas is usually denoted by the letter Q.
The electric charge of an electron is about 1.602176E-19 Coulomb and has a negative sign. The proton has the same charge, but is positive. In a substance, electrons and protons are usually present in equal quantities, so that the total charge is zero. In some cases, the number of electrons can increase, then we say that the body is negatively charged, or decrease, then the body is positively charged.
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