- one of the fundamental laws of nature. The law of conservation of charge was discovered in 1747 by B. Franklin.
Electron- a particle that is part of an atom. In the history of physics, there have been several models of the structure of the atom. One of them, which makes it possible to explain a number of experimental facts, including electrification phenomenon , was proposed E. Rutherford. Based on his experiments, he concluded that at the center of the atom there is a positively charged nucleus, around which negatively charged electrons move in orbits. In a neutral atom, the positive charge of the nucleus is equal to the total negative charge of the electrons. The nucleus of an atom consists of positively charged protons and neutral particles, neutrons. The charge of a proton is equal in absolute value to the charge of an electron. If one or more electrons are removed from a neutral atom, it becomes a positively charged ion; If electrons are added to an atom, it becomes a negatively charged ion.
Knowledge about the structure of the atom allows us to explain the phenomenon of electrification friction . Electrons that are loosely bound to the nucleus can break away from one atom and attach to another. This explains why it can form on one body lack of electrons, and on the other - theirs excess. In this case, the first body becomes charged positively , and the second - negative .
When electrified, it occurs charge redistribution , both bodies are electrified, acquiring charges of equal magnitude and opposite signs. In this case, the algebraic sum of electric charges before and after electrification remains constant:
q 1 + q 2 + … + q n = const.
The algebraic sum of the charges of the plates before and after electrification is equal to zero. The written equality expresses the fundamental law of nature - conservation law electric charge .
Like any physical law, it has certain limits of applicability: it is fair For closed system tel , i.e. for a collection of bodies isolated from other objects.
IN normal conditions microscopic bodies are electrically neutral because the positively and negatively charged particles that form atoms are bonded to each other electrical forces and form neutral systems. If the electrical neutrality of a body is violated, then such a body is called electrified body. To electrify a body, it is necessary that an excess or deficiency of electrons or ions of the same sign be created on it.
Methods of electrifying bodies, which represent the interaction of charged bodies, can be as follows:
- Electrification of bodies upon contact. In this case, during close contact, a small part of the electrons transfers from one substance, in which the connection with the electron is relatively weak, to another substance.
- Electrification of bodies during friction. At the same time, the area of contact between the bodies increases, which leads to increased electrification.
- Influence. The basis of influence is electrostatic induction phenomenon, that is, the induction of an electric charge in a substance placed in a constant electric field.
- Electrification of bodies under the influence of light. The basis of this is photoelectric effect, or photoeffect when, under the influence of light, electrons can fly out of a conductor into the surrounding space, as a result of which the conductor charges.
Numerous experiments show that when there is electrification of the body, then electric charges appear on the bodies, equal in magnitude and opposite in sign.
Negative charge body is caused by an excess of electrons on the body compared to protons, and positive charge caused by a lack of electrons.
When a body is electrified, that is, when a negative charge is partially separated from the positive charge associated with it, law of conservation of electric charge. The law of conservation of charge is valid for a closed system into which charged particles do not enter from the outside and from which they do not leave. The law of conservation of electric charge is formulated as follows:
In a closed system, the algebraic sum of the charges of all particles remains unchanged:
q 1 + q 2 + q 3 + … + q n = const
where q 1, q 2, etc. – particle charges.
Interaction of electrically charged bodies
Interaction of bodies, having charges of the same or different sign, can be demonstrated in the following experiments. We electrify the ebonite stick by friction on the fur and touch it to a metal sleeve suspended on a silk thread. Charges of the same sign (negative charges) are distributed on the sleeve and the ebonite stick. By bringing a negatively charged ebonite stick closer to a charged sleeve, you can see that the sleeve will be repelled from the stick (Fig. 1.2).
Rice. 1.2. Interaction of bodies with charges of the same sign.
If you now bring a glass rod rubbed on silk (positively charged) to the charged sleeve, the sleeve will be attracted to it (Fig. 1.3).
Rice. 1.3. Interaction of bodies with charges of different signs.
It follows that bodies with charges of the same sign (likely charged bodies) repel each other, and bodies with charges of different signs (oppositely charged bodies) attract each other. Similar inputs are obtained if we zoom in on two plumes, similarly charged (Fig. 1.4) and oppositely charged (Fig. 1.5).
Law of conservation of charge
Not all natural phenomena can be understood and explained using the concepts and laws of mechanics, the molecular-kinetic theory of the structure of matter, and thermodynamics. These sciences say nothing about the nature of the forces that bind individual atoms and molecules and hold the atoms and molecules of a substance in a solid state at a certain distance from each other. The laws of interaction of atoms and molecules can be understood and explained on the basis of the idea that electric charges exist in nature.
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 interaction of bodies detected during electrification is called electromagnetic interaction, and physical quantity, which determines the electromagnetic interaction, is an electric charge. The ability of electric charges to attract and repel indicates the presence of two various types charges: positive and negative.
Electric charges can appear not only as a result of electrification when bodies come into contact, but also during other interactions, for example, under the influence of force (piezoelectric effect). But always in a closed system, which does not include charges, for any interactions of bodies, the algebraic (i.e., taking into account the sign) sum of the electric charges of all bodies remains constant. This experimentally established fact is called the law of conservation of electric charge.
Nowhere and never in nature do electric charges of the same sign arise or disappear. The appearance of a positive charge is always accompanied by the appearance of a negative charge equal in absolute value, but opposite in sign. Neither positive nor negative charges can disappear separately from each other if they are equal in absolute value.
The appearance and disappearance of electric charges on bodies in most cases is explained by the transitions of elementary charged particles - electrons - from one body to another. As you know, any atom contains a positively charged nucleus and negatively charged electrons. In a neutral atom, the total charge of electrons is exactly equal to the charge atomic nucleus. A body consisting of neutral atoms and molecules has a total electric charge of zero.
If, as a result of some interaction, part of the electrons passes from one body to another, then one body receives a negative electric charge, and the second one receives a positive charge of equal magnitude. When two differently charged bodies come into contact, usually the electric charges do not disappear without a trace, but the excess number of electrons passes from the negatively charged body to a body in which some of the atoms did not have a full complement of electrons on their shells.
A special case represents the meeting of elementary charged antiparticles, for example, an electron and a positron. In this case, the positive and negative electric charges actually disappear, annihilate, but in full accordance with the law of conservation of electric charge, since the algebraic sum of the charges of the electron and positron is zero.
Law of conservation of electric charge states that the algebraic sum of charges in an electrically closed system is conserved.
The law of conservation of charge is fulfilled absolutely exactly. On this moment its origin is explained as a consequence of the principle of gauge invariance. The requirement of relativistic invariance leads to the fact that the charge conservation law has local character: the change in charge in any predetermined volume is equal to the flow of charge across its boundary. In the original formulation, the following process would be possible: a charge disappears at one point in space and instantly appears at another. However, such a process would be relativistically non-invariant: due to the relativity of simultaneity, in some reference frames the charge would appear in a new place before disappearing in the previous one, and in some, the charge would appear in a new place some time after disappearing in the previous one. That is, there would be a period of time during which the charge is not retained. The locality requirement allows us to write down the charge conservation law in differential and integral form.
Charge conservation law and gauge invariance
| Symmetry in physics | ||
|---|---|---|
| Conversion | Corresponding invariance | Corresponding law conservation |
| ↕ Time broadcasts | Uniformity time | ...energy |
| ⊠ C, P, CP and T symmetries | Isotropy time | ...evenness |
| ↔ Broadcast space | Uniformity space | ...impulse |
| ↺ Rotations of space | Isotropy space | ...of the moment impulse |
| ⇆ Lorentz group | Relativity Lorentz invariance | …4-pulses |
| ~ Gauge transformation | Gauge invariance | ...charge |
Physical theory states that each conservation law is based on a corresponding fundamental principle of symmetry. The laws of conservation of energy, momentum and angular momentum are associated with the properties of space-time symmetries. The laws of conservation of electric, baryon and lepton charges are associated not with the properties of space-time, but with the symmetry of physical laws regarding phase transformations in the abstract space of quantum mechanical operators and state vectors. Charged fields in quantum field theory are described by a complex wave function, where x is the space-time coordinate. Particles with opposite charges correspond to field functions that differ in the sign of the phase, which can be considered an angular coordinate in some fictitious two-dimensional “charge space”. The charge conservation law is a consequence of the invariance of the Lagrangian under a global gauge transformation of type , where Q is the charge of the particle described by the field , and is an arbitrary real number that is a parameter and independent of the space-time coordinates of the particle. Such transformations do not change the modulus of the function, so they are called unitary U(1).
Law of conservation of charge in integral form
Recall that the flux density of an electric charge is simply the current density. The fact that the change in charge in the volume is equal to the total current through the surface can be written in mathematical form:
Here is some arbitrary region in three-dimensional space, - the boundary of this region, - the charge density, - the current density (electric charge flux density) across the boundary.
Law of conservation of charge in differential form
By moving to an infinitesimal volume and using Stokes' theorem as necessary, we can rewrite the charge conservation law in local differential form (continuity equation)
Law of conservation of charge in electronics
Kirchhoff's rules for currents follow directly from the law of conservation of charge. The combination of conductors and radio-electronic components is presented as an open system. The total influx of charges into this system is equal to the total output of charges from the system. Kirchhoff's rules assume that electronic system cannot significantly change its total charge.
Experimental verification
The best experimental test of the law of conservation of electric charge is the search for such decays elementary particles, which would be allowed in the case of non-strict charge conservation. Such decays have never been observed. The best experimental constraint on the probability of violation of the law of conservation of electric charge comes from a search for a photon with the energy mec 2/2 ≈ 255 keV, arising in the hypothetical decay of an electron into a neutrino and a photon:
however, there are theoretical arguments that such single-photon decay cannot occur even if charge is not conserved. Another unusual non-charge-conserving process is the spontaneous transformation of an electron into a positron and the disappearance of charge (transition to additional dimensions, tunneling from the brane, etc.). The best experimental constraints on the disappearance of an electron along with an electric charge and on the beta decay of a neutron without electron emission.