An electric charge is a physical quantity that is inherent in some elementary particles. It manifests itself through the forces of attraction and repulsion between charged bodies through an electromagnetic field. Consider the physical properties of the charge and the types of charges.
General idea of electric charge
Matter, which has a non-zero electric charge, actively interacts with an electromagnetic field and, in turn, creates this field. The interaction of a charged body with an electromagnetic field is one of four types of force interactions that are known to man. Speaking about the charges and types of charges, it should be noted that from the point of view of the standard model, an electric charge reflects the ability of a body or particle to exchange electromagnetic field carriers - photons - with another charged body or electromagnetic field.
One of the important characteristics of various types of charge is the conservation of their sum in an isolated system. That is, the total charge is retained for an arbitrarily long time, regardless of the type of interaction that takes place inside the system.
The electric charge is not continuous. In the experiments of Robert Milliken, the discrete nature of the electric charge was demonstrated. The types of charges that exist in nature can be positive or negative.
Positive and negative charges
Carriers of two types of charges are protons and electrons. For historical reasons, the electron charge is considered negative, has a value of -1 and is denoted by -e. A proton has a positive charge of +1 and is denoted + e.
If the body contains more protons than electrons, then it is considered positively charged. A striking example of the positive type of charge in nature is the charge of a glass rod after it is rubbed with a silk cloth. Accordingly, if the body contains more electrons than protons, it is assumed to be negatively charged. This type of electric charge is observed on a plastic ruler, if rubbed with wool.
Note that the charge of the proton and electron, although very small, is not elementary. Quarks were found - “bricks”, forming elementary particles that have charges ± 1/3 and ± 2/3 relative to the charge of the electron and proton.
unit of measurement
The types of charges, both positive and negative, in the international system of units of SI are measured in pendants. A charge of 1 pendant is a very large charge, which is defined as the number of electrons passing in 1 second through the cross section of the conductor with a current of 1 ampere in it. One pendant corresponds to 6.242 * 10 18 free electrons. This means that the charge of one electron is -1 / (6.242 * 10 18 ) = - 1.602 * 10 -19 coulomb. The same value, only with a plus sign, is characteristic of another type of charges in nature - the positive charge of a proton.
A brief history of electric charge
Ever since ancient Greece, it is known that if you rub your skin on amber, it acquires the ability to attract light bodies, such as straw or feathers of birds. This discovery belongs to the Greek philosopher Thales of Miletus, who lived 2500 years ago.
In 1600, English physician William Gilbert noted that many materials behave like amber when rubbed. The word "amber" in the ancient Greek language sounds like "electron". Gilbert began to use this term for all such phenomena. Other terms later appeared, such as "electricity" and "electric charge." In his work, Gilbert was also able to distinguish between magnetic and electrical phenomena.
The discovery of the existence of attraction and repulsion between electrically charged bodies belongs to physicist Stefan Gray. The first scientist who suggested the existence of two types of electric charges was the French chemist and physicist Charles François Dufe. The phenomenon of electric charge was also investigated in detail by Benjamin Franklin. At the end of the 18th century, the French physicist Charles Augustin de Coulomb discovered his famous law.
Nevertheless, all these observations were able to take shape in a harmonious theory of electricity only by the middle of the XIX century. It should be noted the importance of the work of Michael Faraday on the study of electrolysis and James Maxwell, who fully described electromagnetic phenomena.
Modern ideas about the nature of electricity and discrete electric charge owe their existence to the works of Joseph Thomson, who discovered the electron, and Robert Milliken, who measured its charge.
Magnetic moment and electric charge
Types of charge identified Benjamin Franklin. There are two of them: positive and negative. Two charges of the same sign repel, and the opposite - attract.
With the advent of quantum mechanics and elementary particle physics, it was shown that in addition to the electric charge, particles have a magnetic moment, which is called the spin. Due to the electrical and magnetic properties of elementary particles, an electromagnetic field exists in nature.
The principle of conservation of electric charge
In accordance with the results of many experiments, the principle of conservation of electric charge states that there is no way to destroy the charge or create it out of nothing, and that in any electromagnetic processes in an isolated system, the total electric charge is conserved.
As a result of the electrification process, the total number of protons and electrons does not change; there is only a separation of charges. An electric charge may appear in any part of the system where it did not exist before, but the total charge of the system will still not change.
Electric charge density
Charge density is understood to be its quantity per unit length, area or volume of space. In this regard, they speak of three types of its density: linear, surface, and volume. Since there are two types of charge, the density can also be positive and negative.
Despite the fact that the electric charge is quantized, that is, it is discrete, in a number of experiments and processes the number of its carriers is so large that we can assume that they are distributed uniformly throughout the body. This good approximation provides a number of important experimental laws for electrical phenomena.
Pendant law
Studying the behavior of two point charges on torsion scales, that is, those for which the distance between them significantly exceeds their sizes, Charles Coulomb in 1785 discovered the law of interaction between electric charges. The scientist formulated this law as follows:
The magnitude of each force with which two point charges interact at rest is directly proportional to the product of their electric charges and inversely proportional to the square of the distance separating them. The forces of interaction are directed along the line that connects the charged bodies.
Note that the Coulomb law does not depend on the type of charges: changing the sign of the charge will only change the direction of the acting force in the opposite direction, while preserving its modulus. The proportionality coefficient in the Coulomb law depends on the dielectric constant of the medium in which the charges are considered.
Thus, the formula for the Coulomb force is written as follows: F = k * q 1 * q 2 / r 2 , where q 1, q 2 are the magnitudes of the charges, r is the distance between the charges, k = 9 * 10 9 N * m 2 / CL 2 - proportionality coefficient for vacuum.
The constant k through the universal dielectric constant ε 0 and the dielectric constant of the material ε is expressed as follows: k = 1 / (4 * pi * ε * ε 0 ), here pi is the number pi, and ε> 1 for any medium.
Coulomb's law is not valid in the following cases:
- when charged particles begin to move, and especially when their speeds approach near light speeds;
- when the distance between charges is small compared to their geometric dimensions.
It is interesting to note that the mathematical form of the Coulomb law coincides with that for the law of universal gravitation, in which the mass of the body plays the role of electric charge.
Methods of electric charge transfer and electrification
Electrification is understood as a process as a result of which an electrically neutral body acquires a charge different from zero. This process is associated with the movement of elementary charge carriers, most often electrons. You can electrify the body using the following methods:
- As a result of contact. If a charged body touches another body consisting of a conductive material, the latter will acquire an electric charge.
- Friction of the insulator on other material.
- Electric induction. The essence of this phenomenon is the redistribution of electric charges inside the body due to the influence of an electric external field.
- The phenomenon of the photoelectric effect, in which electrons escape from a solid due to exposure to electromagnetic radiation.
- Electrolysis. Physico-chemical process that occurs in melts and solutions of salts, acids and alkalis.
- Thermoelectric effect. In this case, electrification occurs due to temperature gradients in the body.