In physics,Law of conservation of charge(law of conservation of electric charge)conservation law。There are two versions of charge conservation law, "weak version of charge conservation law" (also called "global charge conservation law") and "strong version of charge conservation law" (also called "local charge conservation law").The weak version of the law of conservation of charge shows that the total charge of the entire universe remains unchanged and will not change with time.Note that this law does not prohibit the sudden disappearance of an electric charge at this end of the universe, but the sudden appearance of an electric charge at that end of the universe.The strong version of the law of conservation of charge explicitly prohibits this possibility.The strong version of the law of conservation of charge shows that the change of the amount of charge in an arbitrary space area is equal to the amount of charge flowing into the area minus the amount of charge flowing out of the area.
American scientists and politiciansFranklinCommunication with friends in 1747:
Here and in Europe, scientists have found and confirmed that electric fire is a real element or material type, not generated by friction, but can only be obtained from collection.
——Benjamin Franklin[1]
The academic community credits Franklin as the founder of this law."Franklin's law of conservation of charge" indicates that in any insulation system, the total charge is constant.[2]
concept
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The law of conservation of charge is physicalFundamental lawone of.It points out that for an isolated system, the algebraic sum of all charges in it will remain unchanged no matter what happens.The law of charge conservation shows that if the charge in a certain area increases or decreases, then there must be an equal amount of charge entering or leaving the area;If a certain charge is generated or disappeared in a physical process, there must be an equal amount of different sign charges generated or disappeared at the same time.
The amount of charge is called the quantity of charge, often referred to as the quantity of electricity, so the law of conservation of charge is also called the law of conservation of electricity.stayInternational System of UnitsThe unit of electric charge is coulomb, which is represented by the letter Q, and the unit is C.Generally, the amount of positive charge is expressed as a positive number, while the amount of negative charge is expressed as a negative number.
principle
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The law of conservation is based on a fundamental principle, namelychargeCan not be generated and annihilated alone.If the positively charged particle contacts the negatively charged particle, and the two particles have the same electric quantity, then because of this contact action, the two particles will become neutral, and this physical behavior is reasonable and allowed.Oneneutron, can also generate positively chargedproton, negatively chargedElectronicsNeutralAntineutrino。However, any particle cannot change the amount of charge alone.Physics explicitly prohibits such physical behavior.More specifically, subatomic particles such as electrons and protons will carry electric charges, and these subatomic particles can be generated or annihilated.In particle physics, the conservation of charge means that the total charge will not change before and after the reaction, although there will be positively charged particles or negatively charged particles in the reactions of basic particles generating charged particles;Similarly, in those elementary particle reactions that annihilate charged particles, although there will be annihilation of positively charged particles or negatively charged particles, the total charge will never change before and after the reaction.
All the above equations are true.Therefore, the integrand can be extracted:
。
The charge conservation equation is also called the charge continuity equation.
In the mid-19th century,James Clerk Maxwell findAmpere's law(Original form) cannot meet the requirements of charge conservation.Therefore, he revised the equation of Ampere's law to Maxwell Ampere equation.Because of this action, Maxwell found thatMaxwell's equations, can be used to describeelectromagnetic waveAnd derive electromagnetic waves tolight speedSpread onfree space。Therefore, he correctly concluded thatlight waveIt is an electromagnetic wave.For more details, see the entryMaxwell's equations。
Indeed, Maxwell's equations have summarized the charge conservation equation.Consider Maxwell Ampere equation,
A large number of experimental facts from friction electrification and other electrification processes show that all electrification processes are actually the process of separating or transferring positive and negative charges on objects. In this process, charges can neither be eliminated nor created, but can only redistribute the original charges.From this, we can conclude the law of charge conservation: the total charge of an isolated system (that is, the algebraic sum of all positive and negative charges in the system) remains unchanged in any physical process.The so-called isolated system refers to a system that has no interaction with the outside world and is an ideal state.The law of conservation of charge is also a basic law of conservation in naturemicrocosmicIt is generally applicable in the field.
Modern physics experiments have found that charged particles can be generated and annihilated under certain conditions.For example, aHigh-energy photonUnder certain conditions, it can produce a positive electron and a negative electron;A pair of positive and negative electrons can annihilate at the same time and convert into photons.However, in these cases, charged particles are always produced and annihilated in pairs. The number of charged particles is equal but the positive and negative are opposite, while the photon is not charged, so the algebraic sum of charges remains unchanged.Therefore, in a system without charge exchange with the outside world, the algebraic sum of charges remains unchanged.It is one of the important basic laws of nature.
Electrostatics
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stayElectrostaticsLi,potentialIt is relative, not absolute.Assume that the potential in three-dimensional space is
, now add a constant c to the potential, and change it to
, the electric field will not change, and this property is calledGauge invariance。Because of this nature, the potential at a certain reference position must be set first, and the potential at other positions can have real physical significance.Therefore, each equation only involves the relative potential, not the absolute potential.
Charge conservation andGauge invarianceClosely related.You can use oneThought experimentTo discuss.Suppose that some process can destroy the conservation of charge (if it cannot be destroyed permanently, it can be destroyed temporarily at least).This process will generate a potential of
Somewhere on
Generate a charge q, and then transfer this charge to a potential of
Location of
And finally annihilate the charge.It is noted that this process does not break the global charge conservation law, but only the local charge conservation law.[3]
It is specified that at any position, the energy W needs to be input to generate the charge, and the energy W will be released when the charge is annihilated.Since the position where the charge is generated or annihilated is arbitrary, W is not related to the relative potential.W is not related to the absolute potential.Then, the whole process will make the system obtain energy
。However, doing so would violate the conservation of energy.In order to observe the conservation of energy, local charge conservation must be required.Therefore, due to gauge invariance, the law of conservation of charge holds.
Experimental evidence
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If the charge is not always conserved, particles may occurdecay。The best experimental method to test the conservation of charge is to find the decay of these particles.So far, physicists have not found any such decay.For example, for electron decayneutrinoPhysicians try to detect the high-energy photons generated by the reaction with photons:[4]
However, some theories suggest that even if the charge is not always conserved, this decay reaction that generates high-energy photons will never occur.Of course, there are also experiments that try to detect the decay that does not produce high-energy photons, or some more unusual charge destruction processes, for example, electrons may spontaneously becomepositron, electronic migration into other dimensions.The best experimental value limit is
Any particle
The average life is more than 6.4 × 10 years (68%)confidence level ）
For all neutron decay events, the occurrence rate of charge nonconservative decay is less than 8 × 10 (68%confidence level ）
