Electric current

Electric Charge

Electric Charge

An electric charge (the amount of electricity) is a physical scalar quantity that determines the ability of bodies to be a source of electromagnetic fields and participate in electromagnetic interaction. The first electric charge was introduced in Coulomb's law in 1785.

The unit of charge in the International System of Units (SI) is the Coulomb: an electric charge that passes through the cross section of a conductor with a current of 1 A for 1 s. The load on a Coulomb is very large. If two load carriers (q 1 = q 2 = 1 C) were placed in a vacuum at a distance of 1 m, then they would interact with a force of 9⋅10 9 H, that is, with the force with which gravity Earth attracts an object that weighs approximately 1 million tons.

As far as we know, the electric charge in nature only occurs in integer multiples of the elementary charge e. It is equal to the proton charge, and has a value of 1,602 176 53 × 10 -19 C. The electron has exactly the same charge, but then negative. Loads that are not multiples of e, only occur in quarks. These are elementary particles, whose charge is a multiple of e / 3, but which, unlike protons and electrons, have never been observed separately.

The quantization of the electric charge

If quarks are not considered, no object has been discovered with a charge lower than that of the electron: for this reason, the value of its charge is considered the fundamental unit of electric charge, and all charge quantities are multiple of charge of electrons However, according to the standard physics model, the smallest particle charges are ± e / 3, ± 2 e / 3 and ± e: for example, the descending quark has a charge - e / 3, the quark up has a charge 2 and / 3, while its antiparticles have opposite charges.

The other quarks, of greater mass, have in any case charges ± and / 3 or ± 2 and / 3. Although quarks carry an electric charge, observing a free quark requires extremely high energy that is recently within the reach of particle accelerators, due to the high intensity of the strong nuclear interactions that hold them together. It is believed that the existence of a plasma of free quarks and gluons at approximately 150 GeV, approximately 1 × 10 12 K; physicists try to achieve this by hitting heavy nuclei, such as gold, at energies of approximately 100 GeV per nucleon.

In addition to the electric charge, we can also define a color charge, which introduces an additional quantum number, used to describe quarks and gluons, along with taste, in the theory of quantum chromodynamics.

The electron

The electron is a subatomic particle that has a resting mass of 9,109 3826 (16) × 10 −31 kg, equal to approximately 1/1836 of that of the proton. The intrinsic angular momentum, or spin, is a semi-integer value of 1/2 in units of ħ, which makes the electron a fermion, therefore subject to the Pauli exclusion principle. The antiparticle of the electron is the positron, which differs only in the opposite electric charge; when these two particles collide they can be diffuse or annihilated producing photons, more precisely gamma rays.

The idea of ​​a fundamental amount of electric charge was introduced by the philosopher Richard Laming in 1838 to explain the chemical properties of the atom; The term electron was coined later in 1894 by the Irish physicist George Johnstone Stoney, and was recognized as a particle by Joseph John Thomson and his research group. Later, his son George Paget Thomson demonstrated the double corpuscular and wave nature of the electron, which is then described by quantum mechanics through wave-particle dualism.

Electrons, together with protons and neutrons, are parts of the structure of atoms and, although they contribute less than 0.06% to the total mass of the atom, they are responsible for their chemical properties; in particular, the exchange of electrons between two or more atoms is the source of the covalent chemical bond.

Most of the electrons in the universe were created during the Big Bang, although this particle can be generated through the beta decay of radioactive isotopes and in high-energy collisions, while it can be annihilated thanks to the collision with the positron and be absorbed in a process of stellar nucleosynthesis.

In many physical phenomena, particularly in electromagnetism and in solid state physics, the electron has an essential role: it is responsible for the conduction of electric current and heat, its movement generates the magnetic field and the variation of its energy is responsible for Photon production

The advent of electronics, where computer science was born, places the electron at the base of the technological development of the twentieth century. Its properties are also exploited in various applications, such as cathode ray tubes, electron microscopes, radiotherapy and lasers.

The electron also belongs to the class of subatomic particles called leptons, which are believed to be fundamental components of matter (that is, they cannot be broken down into smaller particles).


Electrostatics is the section of the doctrine of electricity, which studies the interactions and properties of electric charge systems that are immobile in relation to the chosen inertial reference frame.

The magnitude of the electric charge (otherwise, simply an electric charge) can take positive and negative values; It is a numerical characteristic of load carriers and charged bodies. This value is determined in such a way that the interaction of the force transferred by the field between the charges is directly proportional to the magnitude of the charges that interact with each other particles or bodies, and the directions of the forces acting on them from the side of the electromagnetic field depend on the sign of the charges.

The electrical charge of any body system 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. SSSE Electric charge carriers are electrically charged elementary particles. The smallest mass in the free particle with a negative elementary electric charge is an electron (its mass is 9.11⋅10 −31 kg). The smallest mass-stable antiparticle with a positive elementary charge a positron that has the same mass as an electron. There is also a stable particle with a positive elementary charge: a proton (the mass is 1.67⋅10 −27 kg) and other less common particles. A hypothesis (1964) was raised that there are also particles with a lower charge (± ⅓ and ± ⅔ of the elementary charge) - quarks; however, they are not isolated in the free state (and,

The electrical charge of any elementary particle is an invariably relativistic quantity. It does not depend on the frame of reference, which means that it does not depend on whether this charge moves or rests, it is inherent in this particle throughout its life, therefore, elementary charged particles are often identified with their electrical charges. In general, in nature there are both negative and positive charges. The electrical charges of atoms and molecules are equal to zero, and the charges of positive and negative ions in each cell of the crystalline networks of solids are compensated.

Voltage and capacity of electric charges

The charged particles of the same polarity repel each other with a force that increases quadratically as the distance between the particles decreases. When adding charged particles to a conductor, the distance between the particles decreases, so more and more energy is needed per unit of charge to add additional charge. This is the potential or voltage of that conductor, expressed in volts (V). A driver who takes a lot of load per volt has a high capacity. That ability naturally depends on the dimensions of that driver.

Special constructions have been designed to store as much cargo as possible per volt. These components are called capacitors; they make use of the force of attraction between particles with opposite charge in two closely spaced conductors, to eliminate the repulsive force of particles with equal charge within each conductor.

The charge can also be stored in a metal sphere isolated from the ground (as in the vandigra generator). However, if the charge becomes too large, air leaks will occur due to ionization, which may be accompanied by sparks if there is sufficient charge. The maximum amount of charge (and, therefore, also the electrical voltage) in an electrically conductive sphere depends linearly on the size (diameter) of that sphere. When the sphere is enlarged, the danger to man increases, because the discharge can lead to large currents. With an electrical current of more than 100 mA through the heart muscle of a human being, the risk of cardiac arrest is high.

Forces between electric charges

Coulomb's law expresses the attraction or repulsion of objects charged at rest in the form of a formula. Electric charges cause electric fields, regardless of their state of motion. The forces between stationary charges are studied in electrostatics. Moving electrical charges also cause a magnetic field; This field propagates at the speed of light and, in turn, influences the other mobile charges. Namely, a magnetic field exerts a force lorentz on a charge that crosses the direction of the field, which is perpendicular to both the direction of the field and the direction of movement. This is the cause of the induction phenomenon, described by Faraday's law, and also of a compression effect on the free-charge carriers with the same sign moving in the same direction.

Both attraction and electrostatic repulsion and Lorentz force are contained in Maxwell's broad equations of electromagnetism.




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Last review: August 30, 2019