Electric charge is the positive or negative electricity carried by an object or its constituent particles.Charge is a state attribute of objects. Macroscopic objects or microscopic particles are said to be charged when they are in the charged state.The basic unit symbol of charge is e. Its size is equal to the absolute value of the charged quantity of electrons or protons. The electric quantity of any charged body can only be an integral multiple of this basic unit.[4]
There are two kinds of charges carried by objects or microscopic particles, calledpositive chargeandnegative chargeObjects with the same charge repel each other, and objects with different charges attract each other.The interaction between static charges is calledElectrostatic force。[4]
Experiments have proved that the electric quantity of the charge is independent of its motion state, that is, the electric quantity of charged particles remains unchanged when observed in different reference systems, which is the relativistic invariance of the charge.[4]
The amount of charge is called the "amount of charge".stayInternational System of UnitsThe symbol of the amount of charge isqIs expressed in C (coulomb, referred to as "library").The discipline of studying the interaction of charged matter is called "electrodynamics", which can be divided into classical electrodynamics and quantum electrodynamics.IfQuantum effectCan be ignored, then the classical electrodynamics can accurately describe the physical behavior of charged matter in the electromagnetic field.
At the beginning of the twentieth century, the famousOil drop experimentVerify that the charge hasquantumThe property, that is, the charge is composed of a stack ofelementary chargeConsisting of separate small units.The basic charge is represented by a symbol
Mark, approximately with charge (quantity of electricity)
。Study the relationship between charged particles andphotonThe academic field of media interaction is calledQuantum electrodynamics。
In the laboratory, electroscope is often used to check whether the object is charged.When the charged body contacts the metal ball of the electroscope, part of the charge will be transferred to the two metal foils of the electroscope. The two metal foils with the same charge will open due to mutual repulsion.
history
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Around 600 BC, Thales, the Greek philosopher, recorded that after rubbing cat hair and amber, amber would attract light objects such as feathers. If the rubbing time was long enough, even sparks would appear.[1]
In 1600, Gilbert, an Englishman, first invented the electroscope (Versorium), which can detect electrostatic charges.When the charged object is close to the tip of the metal pointer, because of electrostatic induction, the opposite charge will move to the tip of the pointer, and the pointer and the charged object will attract each other, thus turning the pointer to the charged object.
In 1600, British doctor William Gilbert made a very careful study of electromagnetic phenomena.He pointed out that amber is not the only material that can generate static electricity through friction, and distinguish the different properties of electricity and magnetism [3].He wrote the first scientific book on electricity and magnetism, On Magnets.Gilbert created the new Latin term "electricus" (similar to amber, derived from "\\\\\\\\\\\\\\\\\\\\\\\\.This connection gives the English words "electric" and "electricity", which first appeared in the works of Thomas Browne in 1646Pseudodoxia Epidemica(English titleEnquries Into Very Many Received Tenets and Commonly Presumed Truths）。Then, in 1660, the scientist Otto von Glick invented what may be the first book in historyElectrostatic generator（electrostatic generator）。He fixed a sulfur ball on one end of an iron shaft, and then while rotating the sulfur ball, he rubbed the sulfur ball with dry hands to make the sulfur ball generate electric charges and attract small substances.[1]
Electric charge is the amount of electricity carried by a substance, atom or electron.Unit is C（Coulomb, referred to as "library").A glass rod or rubber rod commonly used in the laboratory will carry only about
C。We often refer to "charged particle" as charge, but charge itself is not a "particle", but we often imagine it as a particle for convenience of description.Therefore, those with more charges are called to have more charges, and the amount of electricity determines the size of the force field (Coulomb force).In addition, according toelectric fieldDirectivity of applied force, charge is divided intopositive chargeWith negative charge, electrons are negatively charged.Objects with the same charge will repel each other, and objects with different charges will attract each other.The force of repulsion or attraction is proportional to the product of electric charges.
Coulomb's law(Coulomb's law), French physicistCoulomb(Charles Augustin de Coulomb, 1736-1806) was discovered in 1785 and later named after himself.Coulomb's law iselectrical scienceThe first quantitative law in the history of development, which makes the research of electricity from qualitative to quantitative stage, is an important milestone in the history of electricity.It points out that the interaction force between the charges at two stationary points in vacuum is inversely proportional to the square of the distance and directly proportional to the product of the electric quantity. The direction of the force is along the line. The charges with the same sign repel each other and the charges with the different sign attract each other.[2]
principle
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The amount of charge is called the amount of charge, that ismaterial、atomorElectronicsAnd so on.The symbol of electric charge isq, the unit is C (coulomb).
We often refer to "charged particles" as charges. In addition, according to the directionality of electric field force, charges can be divided into positive charges and negative charges, and electrons are negatively charged.
Positive charge: It is stipulated that the glass rod rubbed with silk has a positive charge.
Negative charge: It is stipulated that the rubber rod rubbed with fur has negative charge.
Law of conservation of charge
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Statement 1:
Electric charge can neither be created nor destroyed. It can only be transferred from one object to another, or from one part of an object to another.During the transfer, the total charge of the system remains unchanged[3]。
Statement 2:
A system without charge exchange with the outside world, the algebraic sum of charges always remains unchanged[3]。
Amount of electric charge: the amount of electric charge.Unit: C
Minimum charge: the amount of charge carried by the electron.
Elementary charge: minimum charge, using
express,
。The charge amount of all charged bodies is or equal to
, or
Integer multiple of.Therefore, the charge cannot change continuously.
Specific charge: the ratio of the amount of charge to the mass of a charged body.
The way the object is charged
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Electric charge has the property of material object and cannot exist without electrons and protons.The essence of electrification is the process of obtaining or losing electrons.
The essence of electrification: both positive and negative charges are separated to transfer charges.The essence is the transfer of electrons, not the creation of electric charges.
1. Friction electrification
Essence: The transfer of electrons between different objects.
Reason: Different objects have different ability to attract and bind electrons
Charged characteristics: two objects are charged with equal amount of different charges
Electrons are transferred from one object to another.The rubber rod rubbed with fur is negatively charged;The glass rod rubbed with silk is positively charged.
Free electrons:
For example, the electron farthest from the atomic nucleus in the metal will often break away from the atomic nucleus and move freely in the metal. This electron is called free electron.Atoms that lose this electron become positively charged ions. They are arranged inside the metal. Each positive ion vibrates in its own equilibrium position without moving. Only free electrons move, which makes the metal become a conductor.
2. Induction electrification
When a charged body is close to the conductor, due to the mutual attraction or repulsion of charges, the free charges in the conductor will tend to or away from the charged body, so that the end of the conductor close to the charged body will be charged with a different sign, and the end far from the charged body will be charged with the same sign.This phenomenon is called electrostatic induction.The process of electrification of metal conductors by electrostatic induction is called induction electrification.
Essence: Transfer electrons in a metal conductor from one part of an object to another.
Object: Metal conductor.
3. Contact electrification
Electric charge is transferred from one object to another.
Essence: transfer of electrons between different objects
Occurrence condition: charged body contacts another object
Type of charge
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Point charge
charge[1]
Point chargeIt is charged particleidealModel.The real point charge does not exist, only when the distance between charged particles is far greater than the size of particles, or the shape and size of charged particlesInteraction forceWhen the influence of is enough to be ignored, this charged body can be called "point charge".Electrification is an inherent property of matter.There are two kinds of charges:positive electricityCharge and negative charge.Objects due to friction, heatingradialExposureChemical changeFor example, when some electrons are lost, the object is positively charged, and when some electrons are obtained, the object is negatively charged.Objects with excess positive or negative charges are called charged bodies, and charged bodies are customarily sometimes called charges.
There is interaction between charges.staticCharge is generated in the surrounding spaceelectrostatic fieldIn addition to electric field, moving charge also generatesmagnetic field。Therefore, static or moving charges will be affected byElectric field forceOnly moving charges can be affected byMagnetic forceeffect.
Whether an actual charged body can be regarded as a point charge is not only related to the charged body itself, but also depends on the nature of the problem and the accuracy requirements.Point charge is an abstract concept necessary for establishing basic laws and an indispensable analytical means for studying complex problems.For example,Coulomb's law、Lorentz's lawAnd quantitative research on electric field of charged body and interaction between charged bodies,Test chargeThe concept of point charge is applied to the introduction of.
Charge of elementary particles
charge
stayParticle physicsMany particles are charged.Charge is an additive quantum number in particle physics,Law of conservation of chargeIt also applies to particles. The sum of charges of particles before reaction is equal to the sum of charges of particles after reactionelectromagnetismInteraction is strictly established.
features
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There are only two kinds of charge in nature, namely positive charge and negative charge.The charge carried by the glass rod rubbed by silk is called positive charge, and the charge carried by the rubber rod rubbed by fur is called negative charge.
The most basic property of charge is that the same kind of charge repels each other and the different kinds of charge attract each other.One of the inherent properties of matter.amberThe phenomenon that light and small objects can be attracted by friction is the first discovery of electrification of objects.And then discoveredLightning strike, inductionheating、to beamAnd so on can charge objects.There are positive and negative charges, repulsion with the same sign, attraction with the different sign, combination of positive and negative charges, and neutralization with each other;The charge can be transferred. This increases and that decreases, while the total amount remains unchanged.
charge[2]
CorporealBasic unitIs an atom, which consists of electrons andNucleusIs composed of protons andneutronComposition.Electrons are negatively charged, protons are positively charged, and neutrons are uncharged.The so-called uncharged object isNumber of electronsAndProton numberEqual, charged objects are the destruction of this balance.staynatureThere is no charge that exists independently of matter in.In aIsolated systemNo matter what changes have taken place, the total number of electrons and protons remains unchanged, but the combination mode or location has changed, so the charge must be conserved.
In order to illustrate the characteristics of electric charge, we may make some analogy with mass.There are positive and negative charges, so electricity has the difference between repulsion and attraction.However, the masses are only positive and not negative, and they always attract each other. It is this difference that makes electric power shield, but gravity can not.
EinsteinIt describes that the mass varies with the speedrelativityThe electric quantity of electrons, protons and all charged bodies does not change with the speed, so the electric quantity is a relativistic invariant.
The charge hasQuantum propertyThe charge of any object is electronic charge
Integer multiple of,
The exact value of (recommended in 1986) is
。Proton and electron electric quantity（absolute value）The difference is less than
The absolute values of the two are generally considered to be completely equal.The electron is very stable, and its life is estimated to be more than 101 billion years, which is more than what has been predicted so faruniverseIt is much older.[1]
Fractional charge
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so-calledFractional chargeIt refers to the charge that is smaller than the electric quantity of the electron. If it exists, it will shake the position of the electron and proton as the charge unit, which has important theoretical significance.In 1964, M. Gail Mann proposedhadronfromquarkThe theory of composition predicts that there are many kinds of quarks and six kinds of charges.However, there is no project about the existence of fractional charges, which belongs to the field of particle physics theory research.Charge conjugation—Parity（CP）SymmetryThe fundamental symmetry of space and matter has always been the frontier of particle physics.Cronin and Fitch won the award for discovering CP damageNobel Prize。But what they found was only indirect CP damage, which could be caused byWeak actionIt can also be explained by the ultra weak effect.To distinguish them, direct CP violation must be studied.This is not only important for exploring new forces and theories in nature, but also plays a role in understanding the origin of CP damageCriticalityRole of.Since 1964,physical scientistHas been committed to the research of direct CP damage.
Explored the direct CP destruction in the past 40 years, gave a more accurate and self consistent theoretical prediction, and obtainedEuropean Nuclear CenterNA48 andFermilabThe confirmation of two important experiments of KTeV.From this experiment and theory, the existence of direct CP damage in nature was established for the first time, and successfully testedStandard modelThe CP destruction mechanism of the system excludes the ultra weak interaction theory.The project also explains the disturbing particlesphysicsThe so-called ΔI=1/2 rule.It is recognized as the work of "Beijing Group" by international peers and recognized and quoted by major international experts in experiment and theory.This project is very important for CPSpontaneous symmetry breakingSome important physical phenomenological processes in S2HDMsystem study It is pointed out that S2HDM can be a new physical model for the origin of CP damage.Breaking of the charge parity symmetry and quarks-LeptonIn terms of theoretical research on taste physics,Wu YueliangAs the main completion person in the internationalcoreThe journal has published dozens of papers, with a total citation rate of more than 1000 times.Published in the United States《Physical Review Letters 》(PRL).
experiment
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Student experiment to verify two kinds of charges:
(3) Support.In order to avoid the loss of electric charge in the experiment, it is better for two students to operate at the same time.
Experiment process:
(1) At the same time, the two students rubbed the glass rod with silk to make it electrified, and put one on the support.Note: remember which end is charged. Do not touch the charged end with your hand. Use the charged end of another glass rod close to the charged end of this glass rod to observe the phenomenon.
(2) Rub the rubber rod with fur and repeat the experiment.
(3) Do the experiment just now with the glass rod rubbed with silk and the rubber rod rubbed with fur.
Experiment summary;People have done a lot of experiments with a variety of materials. People found that charged objects that attract each other with glass rods rubbed with silk must repel each other with rubber rods rubbed with fur;Any rubber rod rubbed with fur attracts each other, and must repel the glass rod rubbed with silk.In other words, the charge of the object is either the same as that of the glass rod rubbed with silk or the rubber rod rubbed with fur. There is no third possibility.
There are only two kinds of electric charges in nature, American scientistsFranklinProvisions are made for these two kinds of charges: the charge carried by the glass rod rubbed with silk is called positive charge, and the charge carried by the glass rod rubbed with fur is called positive chargeRubber rodThe charge is called negative charge.
The interaction between charges has the following laws: ① Like repels, unlike attracts, and the size uses Coulomb's law
To calculate. ②The point charge force is a pair of interaction forcesNewton's Third Law。③Applicable conditions of Coulomb's law:vacuumThe interaction force between charges at the rest point in the middle (even charged bodies, even charged spherical shells can also be used).
In 1865,maxwell(J. C. Maxwell, 1831~1879) proposed on the basis of summarizing previous experimental lawselectromagnetic fieldEquations, and predict from his equationselectromagnetic waveThe existence of lightElectromagnetic essence。
In 1887,hertz(H. Hertz, 1857~1894) confirmed the existence of electromagnetic waves by experiments, andMaxwell's equationsIt is sorted out and simplified.
In 1897,Thomson(J. J. Thomson, 1856~1940)Cathode rayElectron (e -) was found in the tube, which is the first discovery in human historyElementary particle。Physicists have found a large number of charged orElectroneutralityParticles, including protons (p)positron(e+) and neutrons (n).
Discovery of charged elementary particles
1897 - J. J. Thomson discovered the electron in the cathode ray experiment, which is the first basic particle discovered by human beings.
1905~1913 - R. A. Millikan experimented with "oil drop" for many timesmeasureElectronicalCharge mass ratio。
1911 - E. Rutherford based on thescatteringExperiment, propose a nuclear model of the atom;
1920 - E. Rutherford conjectured that in addition to the existence of positively charged "protons" in the nucleus, there should also be a neutral particle.
1930 - A. M. Dirac introduced relativityquantum mechanics, proposed the relativistic quantum theory, predicted the existence of electronsAntiparticle——Positron (also predicted to existMagnetic monopole）。
1932 - C. D. Anderson found positrons in cosmic rays, confirming Dirac's prediction.J. Chadwick discovered neutrons, confirming Rutherford's conjecture.W. K. Heisenberg andIvanThe annual division is established separatelyNucleusA hypothesis consisting of protons and neutrons.
1950 - C. F. Powell incosmic rayThe p meson was found in.
1937 - C. D. Anderson discovered m-son in cosmic rays.
1947 - Successively in cosmic ray andacceleratorA batch ofExotic particle: L hyperon, K meson, X hyperon, W hyperon.
1955 - O. Chamberlain and E. G. Segre found in acceleratorAntiproton。
1964 - M. Gell Mann and G. Zweig proposedQuark modelSince the 1980s, quarks andAntiquark(The heaviest t-quark was not discovered until 1995).
1964 - A group of scientists in EuropeNucleon center(CERN) found in the acceleratorAntideuteron。
1983 - C. Rubbia et al. found at the European Nuclear CenterUnified theory of electroweakThe predicted W ± and Z0 particles.
Connection with life
You may have heard that some people are attracted by electricity when they get an electric shock, while others are turned on by electricity when they get an electric shock. What's the matter?
It turns out that electric shock is when a part of the human body touches a charged body, and a current passes through the human body.After an electric shock, the main reaction is that the nerve is strongly stimulated, causing muscle contraction.As we all know, the movement of the hand mainly depends on the movement of the fingers, which can only move towards the palm of the hand.When the current is small, if you touch the charged body with the inside of your fingers or the palm of your hand, only the contraction of your hand muscles will make you firmly hold the charged body, which is called electroshock.If the finger tip or the outside of the finger (the back of the hand) contacts the electrified body, the strong contraction of the muscle will make the hand break away from the electrified body quickly, which is called electric striking.In addition, when contacting a high-voltage charged body, the current passing through the human body is very large, which may be the whole body or local nerves of the human bodyparalysisAt this time, the human body can not get rid of the charged body, and it looks like it is attracted by electricity.If the power supply is not cut off in time under the condition of electric suction, the person who gets an electric shock will soon burn his skin and breatheasphyxia、heartStopping, causingFeign deathStatus.If you do not rescue in time, you will die.
