electromagnetics

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Electromagnetism is a research Electromagnetic phenomenon Law and application of Branch of Physics Discipline, originated in the 18th century. In a broad sense, electromagnetism can be said to include electricity and magnetism, but in a narrow sense, it is a discipline to explore the interaction between electricity and magnetism. Main research electromagnetic wave 、 electromagnetic field And the dynamics of charges and charged objects.

Chinese name: electromagnetics
Foreign name: electromagnetism
Japanese name: Electromagnetism

Arabic: الكهرومغناطيسية
French: electromagnétisme
Discipline code: fourteen thousand and thirty-five^[3-4]

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Introduction to Physics

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electromagnetics

Electromagnetism studies the interaction between electricity, magnetism and the two, as well as their laws and applications Branch of Physics Discipline. According to the viewpoint of modern physics, the phenomenon of magnetism is caused by moving charges, so it must contain the content of magnetism to varying degrees within the scope of electricity. Therefore, it is difficult to divide the contents of electromagnetism and electricity completely, and "electricity" is sometimes referred to as "electromagnetism".

Electromagnetism has developed from two independent sciences (electricity and magnetism) to a complete branch of physics, mainly based on two important experimental discoveries, namely, the magnetic effect of current and the changing magnetic field Electric effect 。 These two experimental phenomena, together with Maxwell's hypothesis about changing electric field to produce magnetic field, established the whole electromagnetism Theoretical system And developed electrical and electronic technologies that have had a significant impact on modern civilization.

The current carried by the wire will generate a magnetic field around it Magnetic field line Yes Concentric circle The pattern surrounds the wire.

use ammeter Can be measured directly electric current 。 But the disadvantage of this method is that the circuit must be cut off and the ammeter placed in the middle of the circuit. The current intensity can also be measured by indirectly measuring the magnetic field around the current tracing. The advantage is that there is no need to cut off the circuit. The instruments that use this method to measure current are Hall effect Sensors Current clamp （current clamp）、 converter (current transformer), Rogowski coil, etc.

The discovery of electrons combined electromagnetism with the theory of the structure of atoms and matter Electronic theory The macroscopic electromagnetic and optical properties of matter are attributed to the effect of electrons in atoms, which uniformly explains electricity, magnetism Photophenomenon 。

Electromagnetism is a branch of physics. Electricity and magnetism The field has a close relationship. In a broad sense, electromagnetism can be said to include electricity and magnetism, but in a narrow sense, it is a discipline to explore the interaction between electricity and magnetism. Main research electromagnetic wave 、 electromagnetic field And the dynamics of charges and charged objects.

physical phenomenon

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People have known for a long time that Electric fish (electric fish) will send out electric shock. According to 2750 BC Ancient Egypt Books, these electric fish are called“ the Nile The "Thunder Messenger" is the protector of all other fish. About 2500 years later, the Greeks, Romans, Arab naturalists and Arab medicine Only then did the record of generating electricity fish appear again. Ancient Rome The doctor Scribonius Larges also suggested that patients with symptoms like gout Or patients with headaches, go and touch Torpedo ray Maybe strong electric shock will cure their disease.^[1]

Arabs may be the first group to understand the essence of lightning. They may also recognize other sources of electricity before other ethnic groups. As early as the 15th century, the Arabs created the Arabic word "raad" for "lightning" and used it to call the ray.

stay mediterranean sea In the ancient culture of the region, there have been written records for a long time that after rubbing the amber stick with cat hair, it will attract materials such as feathers. Around 600 BC, ancient Greek Philosopher of Thales (Thales, from 640 to 546) made a series of observations on static electricity. From these observations, he believed that friction made amber magnetic. This is like ore magnetite Are quite different in nature; Magnetite is naturally magnetic. Thales is not right. But then, Science Society Verify the close relationship between magnetism and electricity.^[2]

In 1600, it was Britain Elizabeth I Gilbert, an English physician, published On Magnets, summarizing the experience of predecessors and recording a large number of experiments. Such as the "small earth" experiment. Galileo Call it“ empiricism The founder of ".

In 1663, in Madburg, Germany Otto Von Guericke Invention friction Starting motor 。

In 1720, the English priest Gray studied the phenomenon of electricity conduction.

In 1733, Du Fei distinguished two kinds of electricity—— Turpentine Electricity and glass electricity.

In 1745, Netherlands Leiden city Leiden University Professor Musschenbrock found Leiden bottle , found a way to store the charge. The Leiden bottle is one Glass bottles , respectively pasted inside and outside the bottle Tinfoil 。 The tin foil in the bottle is connected with a metal rod through a metal chain, and the upper end of the rod is a metal ball. French Nolet invited France in front of a cathedral in Paris Louis XV The royal family members of Monk Hold hands in a line. The monk at the head of the line holds the Leiden bottle in his hand. When the Leiden bottle is charged, let the monk at the end of the line touch the lead of the Leiden bottle. Suddenly, seven hundred monks jumped up almost at the same time. The people present were dumbfounded. This shows the great power of electricity.

Physical development

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electromagnetic wave Because of historical reasons (at the earliest time, magnetism was considered to be a phenomenon unrelated to electrical independence) magnetism Its own development and application, such as modern times magnetic material And the development of magnetic technology, new Magnetic effect and Magnetic phenomenon The discovery and application of, etc., make the content of magnetism continuously expand, and magnetism is actually studied as a parallel discipline with electricity.

maxwell Electromagnetic theory The significance of this theory is not only that it dominates all macroeconomics Electromagnetic phenomenon (including static electricity, stable magnetic field, electromagnetic induction, circuit, electromagnetic wave, etc.) Optical phenomenon Unification within this theoretical framework profoundly affects people's understanding Material world The idea of.

The disciplines closely related to electromagnetism are Classical electrodynamics There is no principle difference between the two in terms of research object and content. Generally speaking, electromagnetism focuses on classical electromagnetic phenomena experimental study The basic laws of electromagnetism are summarized from extensive research on electromagnetic phenomena, and finally Maxwell's equations (but not system study How to solve it); However, classical electrodynamics focuses on theory, which is based on Maxwell's equations and Lorentz force (logically equivalent to Newtonian mechanics Three of Newton in Law of motion ）Based on the research of macro low-energy Electromagnetic problems such as the distribution of electromagnetic field, the excitation, radiation and propagation of electromagnetic wave, and the interaction between charged particles and electromagnetic field at scale.

Various experimental conclusions of electromagnetics and electrodynamics The relationship between Kepler's three laws And Newton's law of universal gravitation. From high school physics, although Law of universal gravitation From Kepler Yes Celestial motion The three laws summarized from observation are derived simultaneously; And through the simultaneous law of universal gravitation Newton's law of motion With various kinematic quantities Definitional expression We can also reverse the three laws of Kepler's planetary motion (including the expression ）。 However, for many planetary motion problems with specific known conditions, direct use of Kepler's three laws can often avoid a large number of tedious operations.

It can be seen from this that, in a sense, the generalized electromagnetics can also be considered as including classical electrodynamics. about relativity and Quantum Theory For the influence on the development of electromagnetism, see Relativistic electrodynamics 、 Quantum electrodynamics 。

After Maxwell's Electromagnetic Theory was published, due to the difficulty in understanding the theory and no experimental verification, it was not paid attention to and generally recognized for a long time. In 1879, Berlin Academy The award-winning essay is set up to prove the following three assumptions: ① if displacement current exists, magnetic effect will be generated; ② The changing magnetic force must make insulator Media generation Displacement current ；③ In air or vacuum, the above two assumptions are also true. This essay became the forerunner of Hertz's electromagnetic wave experiment.

In 1885, Hertz used a winding Of Oscillating coil Through experiment, it was found accidentally that when a pulse current When, Secondary winding Between the slits at both ends electric spark Hertz immediately thought that this might be an electromagnetic resonance Phenomenon. Since the primary coil Oscillating current Can arouse Secondary coil Then it can generate oscillating displacement current in the adjacent medium, and this displacement current will in turn affect the strength change of the spark in the secondary winding.

In 1886, Hertz designed a linear open oscillator Ring conductor C with clearance is used as a sensor , placed near the linear oscillator AB, when the pulse current is input to AB and sparks are generated in the gap, sparks are also generated in the gap C. In fact, this is the generation, propagation and reception of electromagnetic waves.

To prove the consistency of electromagnetic waves and light waves: Hertz measured the speed of electromagnetic waves in March 1888, and introduced the measurement method in the paper "On electromagnetic waves in the air and their reflection": Hertz formed by using electromagnetic waves standing wave Determine two adjacent Nodal Distance between（ Half wavelength ）， Recombine Vibrator Calculate the speed of the electromagnetic wave. He nailed a piece of lead on one wall of a large room to reflect electromagnetic waves to form standing waves. A tributary vibrator is used at a distance of 13 meters Wave source 。 Use one Induction coil As Checker , moving forward and backward along the standing wave direction, the tester does not produce sparks at the wave node, and the sparks generated at the wave belly are the strongest. This method is used to measure the length between two wave nodes, so as to determine that the speed of electromagnetic waves is equal to the speed of light. In 1887, he also designed "Induction" Balancer ”: In 1886, a metal plate D was placed on one side of the device, and then C was adjusted far so that there was no spark in the gap, and then the metal plate D was moved to the AB and C directions, and an electric spark appeared in the gap of C. This is because the oscillating current induced in D generates an additional electromagnetic field to act on C. When D approaches, the balance of C is destroyed. This experiment shows that the oscillator AB polarizes the nearby medium alternately to form a variable displacement current, which in turn affects the Equilibrium state 。 Spark C. When D approaches C, the balance state is broken again, and C sparks again. This proves the existence of "displacement current".

Hertz makes electromagnetic wave reflect at an angle of 45 ° with metal surface; Use metal Concave mirror Focusing electromagnetic waves; The electromagnetic wave is polarized by a metal grid; And using Non metallic materials The made big prism refracts electromagnetic waves, etc. To prove that Maxwell Electromagnetic theory of light Is correct. So far Maxwell Electromagnetic field theory Was recognized by people. For this reason, Maxwell is recognized as "the greatest mathematics in the world since Newton physical scientist ”。 So far by Faraday Maxwell established the electromagnetic field theory verified by Hertz and declared its victory to the world.

Magnetic effect

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For more than 200 years since Gilbert began, electricity and magnetism have been two unrelated subjects Electricity and magnetism seek natural phenomena The connection between them has become a trend. In 1820, Oster Found Magnetic effect of current , following Thales 2400 years later, the connection between electricity and magnetism was established.

"Dunmou embellishes mustard, magnet needle" explains Magnetic phenomenon 。 At the beginning of the 17th century, Gilbert asserted that there was no causal relationship ； Coulomb They also hold the same view. But: In 1731, a box of new knives of an English businessman was magnetized after lightning; Both electric power and magnetic force comply with Inverse square law , indicating that they have similar laws. In 1751, Franklin found that the sewing needle was magnetized after being discharged by the Leiden bottle. In 1774, a German research institute hung a prize to ask for a solution. The title was: "Is there any real and physical Similarity ？”

Auster (1777-1851), Danish, found Current magnetic effect First person of. In his doctoral thesis "On the Basic Metaphysical Categories of External Nature" in 1799, he expounded Kantian philosophy The guiding role of thought in science is deeply reflected in Kant's“ Fundamental force ”The influence of ideas that can be transformed into other forms of force. In 1803, when traveling to Germany, I met a young German chemist who believed in the interrelationship between chemical phenomena, current and magnetism Ritter , also participated in some experiments carried out by Ritter to find this connection. All these laid the foundation for Oster to discover the current magnetic effect.

(1) In 1803, he said: "People's physics will no longer be a scattered list of motion, heat, air, light, electricity, magnetism and any other phenomena that people know. People will put the whole universe into a system." He believed that“ natural force Unification ".

(2) In 1812, he published Research on the Identity of Chemical Force and Electric Power, which showed that he had applied the unified thought of natural force to the research of physics and chemistry. From the phenomenon that the wire will generate heat when the current flows through the wire with smaller diameter, he speculated that if the diameter of the wire is smaller, it may emit light, and if the diameter continues to decrease, it will produce magnetism. It also pointed out that "people should test whether electricity is the most hidden way to magnet Has an impact. "

(3) However, he believed that the effect of current on the magnet was longitudinal (i.e. along the direction of current), so his guess has not been realized. He put a wire in front of the electrified wire magnetic needle , trying to attract the magnetic needle with an energized wire. However, the wire was hot, even red, and the magnetic needle did not move. But Oster believes that electricity and magnetism have some connection, just like Dina and fever The phenomenon of luminescence is the same.

(4) From the winter of 1819 to April of 1820, Auster was teaching students "Electricity Galvanic current and magnetism ”He considered: Magnetic effect Is it a lateral (transverse) action to scatter around like the heat and light generated when the current passes through the wire? In a lecture, he tried to place the magnetic needle on the side of the wire. When he turn on electricity I found that the magnetic needle shook slightly! It was this slight shaking that made Auster immediately realize that what he had been striving for for years was coming true. After repeated experiments, Oster found out that the current had a magnetic effect. On July 21, 1820, he published Experiments on the Effect of Electric Current on Magnetic Needle, which caused a sensation in the academic world.

(5) Electrical conflict and helical line Oster called this effect occurring in the space around the conductor "electric conflict" and pointed out that "this conflict appears as a circle, otherwise it is impossible to explain this phenomenon: when the magnetic pole is placed below the wire, the magnetic pole is pushed to the east; when the magnetic pole is placed above the wire, the magnetic pole is pushed to the west. The reason is that only a circle has such a property,

The movement of the opposite part has opposite direction. In addition, the circular motion that moves continuously along the length direction of the conductor must be formed Cochlear line Or spiral. "

(6) Rotating force and central force: Oster's discovery and Newtonian mechanics The basic principles of are contradictory. In Newtonian mechanics, the force in nature can only be the attraction or repulsion force acting on the connecting line of the object, that is, the "central force" of the direct push-pull nature. What Oster found was a kind of "rotating force". What he called "spiral" is actually about magnetism Transverse effect Or the visual description of eddy current magnetic field caused by current. It is the beginning of the thought of "field".

Physical theory

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physical analogy

In 1855, he published "On Faraday Force line 》He made a mathematical description of Faraday's force line from a geometric point of view. He wrote in the article: "If people draw a line from any point, and when people walk along this line, the direction of any point on the line always coincides with the direction of the force at that point, then this curve represents the direction of the resultant force of the points he passes through, and in this sense it is called a force line. In the same way, people can draw other force lines. Until the curve fills the entire space to indicate the direction of any specified point. " So, the force line tangent The direction is Electric field force The density of the force line represents the magnitude of the electric field force.

Maxwell regarded the force line as incompressible fluid by analogy streamline 。 So he put the force line Force tube Equivalency fluid mechanics Compare the theories of negative charge As the source and sink of fluid, power line Comparisons Flow tube ， electric field intensity Compared with velocity, a new vector function is introduced to describe the electromagnetic field. It can be said that the physics of Faraday was translated into mathematics. In this article, Maxwell derived the Magnetic line of force The relationship between and magnetic force represents some information describing current and magnetic force line physical quantity Between Quantitative relationship Vector of differential equation , and current Force and Law of electromagnetic induction Quantitative formula of. When Faraday saw Maxwell's article, he exclaimed, "I was surprised to see that this topic was handled so well!"

In 1860, Faraday, who was 70 years old, met Maxwell, a young man of 30 years old. The common aspiration to establish electromagnetic theory transcended the gap of age. Faraday said to Maxwell, "You should not stop explaining my point of view with mathematics, but break through it."

Ether vortex model

In 1862, Maxwell published his second paper on electromagnetism《 On physical force lines 》。 Maxwell introduced a medium The theory of the electromagnetic ether model is proposed to show the relationship between electrical and magnetic quantities. such model theory The medium filled with space has the property of rotation under the action of magnetism, that is, many molecules are arranged vortex , they are formed on the axis of magnetic lines of force Vortex tube , vortex tube rotating angular velocity Proportional to magnetic field intensity H， The density of vortex medium is proportional to the medium Permeability μ。 The centrifugal effect of vortex tube rotation makes the tube expand laterally and contract longitudinally.

The centrifugal effect of vortex tube rotation makes the tube expand laterally and contract longitudinally. Therefore, the magnetic line of force in the longitudinal performance of tension, that is, the attraction of the opposite magnetic pole; In the transverse direction, it is the pressure, that is, the repulsion of the same magnetic pole.

Ether vortex model

Due to mutual Tight connection The surface of the vortex tube is moving in the opposite direction. In order not to interfere with each other's movement, Maxwell envisions a layer of inert or Ball bearing Small particles that act. They are far more than vortex dimension Small, negligible quality charged particle 。 The role of particles and vortices is Tangential direction Of. Particles can roll, but not slide; In uniform Constant magnetic field That is, when the rotating speed of each vortex tube is the same, these particles only rotate around their own axis, but when the rotating speed of the vortex tubes on both sides is different, the center of the particles will vortex on both sides Marginal movement The difference of the situation. For non Uniform magnetic field That is, the strength of the magnetic force varies with the position, so the rotating speed of the vortex tube is also different, and the particles between the vortex tubes move. according to Vortex theory , unit time passing unit area Number of particles That is, the flow j of vortex and the tangent speed H of vortex tube rotation curl Is proportional, that is, where j corresponds to the current, H corresponds to the magnetic field, and this equation is the Equation of motion 。 It shows that the movement of the electric particles must be accompanied by the movement of the magnetic vortex of the molecule, which is the analogy mechanism of the magnetic field lines generated by the current. For the case that the magnetic field changes with time, the energy change of vortex motion (due to the change of H) must be subject to the force from the tangential motion of the particle layer, and this force E satisfies the relationship: where? H/? T is the change rate of vortex velocity, E is the force acting on the particle layer, corresponding to the induced electromotive force at this point. It explains Magnetic medium The unstable magnetic vortex motion in the Induced electromotive force To generate current. This formula is the kinetic equation 。

Displacement current

Proposition of "displacement current": in the third part of the paper, Maxwell extended the vortex model to Electrostatic phenomenon 。 Since H=0, the medium is composed of elastic static vortex tube and particle layer. When the medium is in an electric field, the particle layer will be displaced by the action of electric force E, and the vortex tube will be deformed by a tangential force. The deformed vortex tube exerts an equal and opposite force on the particle layer due to the internal elastic tension Balance of two forces When the particle is in Quiescent state 。 At this time Electric field energy Change into Elastic potential energy 。

about Insulating medium Maxwell further assumed that the particles of the insulating medium affected by electricity would be in a polarized state. Although the particles could not move freely, the impact of electricity on the whole medium was one of the factors that caused electricity in a certain direction Total displacement D。 When the electric field changes, the total displacement D of the particles also changes, thus forming a current in the positive and negative directions. This means that, Electric displacement On time wechat Business ? D/? T must also have the same effect as current. This is it. Maxwell theory The important "displacement current" assumption in.

Max Welley used the electromagnetic ether he constructed mechanical model 。 It not only explains the application properties of Faraday magnetic lines of force, but also establishes the relations between all the main electromagnetic phenomena; However, Maxwell clearly recognized the temporality of the above model, and he only regarded it as a "mechanically conceivable and easy to study model suitable for revealing the true mechanical connection between known electromagnetic phenomena". So in his 1864-1865 paper "Dynamic Theory of Electromagnetic Field", he completely abandoned this model, removed the hypothesis about the medium structure, and only based on a few basic experimental facts field theory The point of view has reconstructed its own theory.

He said, "The theory I put forward can be called electromagnetic field theory, because it must involve Charged body and Magnetic material Surrounding space; It can also be called dynamic theory, because it assumes that there are moving substances in the space, which produces the electromagnetic phenomenon observed by people. " "Electromagnetic field is the space around objects in electromagnetic state, including these objects themselves: there can be only some kind of substance in the field, or there can be take a percentage Space without macroscopic matter, like Geissler Tube or other conditions called vacuum. Maxwell assumed that although there is no "macro matter" in vacuum, there is ether medium. This etheric medium fills the whole space, penetrates the interior of the object, and has energy density And can propagate at a limited speed Electromagnetic action 。

Electromagnetic equations

maxwell

In 1873, Maxwell published General Theory of Electromagnetism. He not only developed Faraday's thought with mathematical theory, but also creatively established a complete system of electromagnetic field theory. In this book, his thoughts have been developed more perfectly and stated more systematically. He integrated the previous electromagnetic theory into a group equation The mathematical equations of electromagnetic field Maxwell electromagnetic equations are obtained. In a terse Mathematical structure The perfect symmetry of electric field and magnetic field is revealed. General Theory of Electromagnetism is the first book about Classical field theory The immortal work of. Initially, in the book "General Theory of Electromagnetism", Maxwell listed a total of 20 component equations. If vector equations were used, there would be only 8. Later, it was simplified into four. Around 1890, German physicist Hertz and British physicist heaviside The Maxwell equations were simplified twice again, and then the general Differential form 。

Prediction of electromagnetic waves

An important result of Maxwell's equations is to predict the existence of electromagnetic waves. Maxwell derived from the equations by calculation free space Medium electric field strength E and Magnetic induction B's wave equation It means that electrical or magnetic disturbances will propagate at the speed of c. And introduced the propagation velocity Is: 3107400 km/s, where ε is Dielectric constant , μ is the permeability.

Light waves are electromagnetic waves

Maxwell found that this value was very close to the light speed of 315000 km/s measured by Fizeau in 1849. He thought it was not a coincidence, but because the essence of light was the same as electromagnetic waves, he proposed Electromagnetic theory of light 。 It shows that "light itself is an electromagnetic vibration that propagates in the form of waves in the electromagnetic field according to the electromagnetic law". Thus, the theory of electricity, magnetism and light has been greatly integrated.

Maxwell said, "Put mathematical analysis The physical knowledge obtained by combining with experimental research is more solid, beneficial and consolidated than the knowledge that a simple experimenter or a simple mathematician can have ".

Special relativity

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electromagnetics

Electromagnetic basic equation by Maxwell's equations , this Equations stay classical mechanics Of relative motion Conversion（ Galileo transformation ）The following form will change. Under Galileo transformation, the speed of light will be different under different inertial coordinates. The transformation keeping the form of Maxwell equations unchanged is Lorentz transformation , under this transformation, different Inertial coordinate The speed of light is constant.

The support of Michelson Morey experiment in the early 20th century Constant speed of light The constant speed of light has also become Einstein's Special relativity The cornerstone of. Instead, Lorentz transformation becomes more precise inertia than Galileo transformation coordinate transformation Mode.

Basic physical formula

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Coulomb's law ：F=kQq/r²;

electric field intensity ：E=F/q

Point charge Electric field intensity: E=kQ/r ²

Uniform electric field ：E=U/d

Electric potential energy ：EA=qφA EA: Charged body stay Point A Electric potential energy (J), q: electric quantity (C), φ A: electric potential at point A (V)

Potential difference ：Uab=Wab/q

Electrostatic force Work : W=qU, U is the potential difference of the electric field at the beginning and end of the charge movement, and q is the electric quantity of the charge.

capacitance Definitional expression ：C=Q/U

Capacitance: C=ε S/4 π kd

electromagnetics

charged particle Movement in a uniform electric field:

Accelerated uniform electric field: 1/2 * mv ^ 2= QU or v ^ 2=2qU/m

Deflection uniform electric field:

Exercise time :t=x/v

vertical acceleration ：a=qU/md

Vertical displacement: y=1/2 * at ^ 2=1/2 * (qU/md) * (x/v//) ^ 2

Deflection angle ：θ=v⊥/v//=qUx/md(v//)^2

Micro current: I=nesv

Ohm's law ：I=U/R

Resistance in series: R=R+ R?+R?+ ……

Resistance parallel connection: 1/R=1/R+ 1/R?+ 1/R?+ ……

Joule's law ：Q=I² Rt

P=I² R

P=U² /R

Electric power ：W=UIt

electromagnetics

electric power ：P=UI

Resistance law ：R=ρl/S

Ohm's law of the whole circuit ：ε=I(R+r)

ε=U outside+U inside

Amberi ：F=ILBsinθ

Lorentz force ：f=qvB

Magnetic flux ：Φ=BS

electromagnetic induction

Induced electromotive force ：E=nΔΦ/Δt

Motional electromotive force ：E=Blv*sinθ

General Arrangement of Electromagnetism Formulas in High School Physics

The electronic quantity is coulomb (Coul), 1C=electronic quantity.

Series circuit

Current I (A) I=I one =I two =...... The current is equal everywhere

Voltage U (V) U=U one +U two +...... Starting from series circuit partial pressure effect

Resistance R (Ω) R=R one +R two +……

parallel connection Circuit

Current I (A) I=I1+I2+ Trunk road The current is equal to the sum of branch currents (shunt)

Voltage U (V) U=U1=U2=

Resistance 1/R (Ω)=1/R one +1/R two

Founders

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Maxwell was a great British physicist in the 19th century and the founder of classical electrodynamics, Statistical Physics One of the founders of.

Maxwell was born on June 13, 1831 Edinburgh 。 Entered at the age of 16 University of Edinburgh , transferred to Cambridge University to study mathematics three years later, graduated in 1854 and stayed at the university to teach, and arrived two years later Scotland Marishar College natural philosophy Professor, 1860 to King's College London Teaching, appointed in 1871 for preparation University of Cambridge Cavendish Lab , and served as the first director. He died in Cambridge on November 5, 1879.

Maxwell integrated and developed Faraday about Electromagnetic interaction And published the famous paper Electromagnetic Field Dynamics Theory in 1865 Electromagnetic phenomenon Summarize into a group Partial differential equations , predicted the existence of electromagnetic waves, and confirmed that light is also a electromagnetic wave To create a classic electrodynamics 。 Maxwell is still here Theory of gas motion , optics thermodynamics , elasticity theory, etc.

Electromagnetism electrodynamics Or classical electrodynamics. It is called classic because it does not include modern Quantum electrodynamics Content of. The term electrodynamics is not strictly used. Sometimes it is also used to refer to the removal of Electrostatics 、 Magnetostatics The rest refers to the combination of electromagnetism and mechanics. This part deals with electromagnetic field yes charged particle The mechanical effect of.

Chronology

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time	Major events	Discoverer
7th century BC	Find magnet	Pipe (China), Thales (Thales, Ancient Greece)
Second century BC	Electrostatic attraction	The early years of the Western Han Dynasty are unknown
1600	Geomagnetism discusses magnetism and introduces "electric"	William Gilbert Her Majesty
1745	Leiden bottle, prototype of capacitor, storing electricity	Pieter van musschenbrock Ewald Georg Von Kleit (Klest, Germany)
1747	Law of conservation of charge (Introduction of positive and negative electricity)	Benjamim Franktin (Franklin, USA)
1754	Lightning arrester (Practical application of electricity)	Procopius Dirisch (Divesh)
1785	Coulomb's law Electromagnetism enters the scientific ranks	Charles Auguste de Coulom (Coulomb, France)
1799	Invention of battery Provide current for a long time	Alessandro Graf Volta (Volta, Italy)
1820	Magnetic effect of current (Electricity generates magnetism) Ampere molecular current theory Biot Savart law	Hans Chanstian Oersted (Austin Denmark) Andre Marie Ampere (Ampere, France) Jean Baptute Biot, Felix Savart (Biot, Savart)
1826	Ohm's law	Georg Simon ohm
1831	Electromagnetic induction phenomenon (Magnetism generates electricity)	Michael Faraday (Faraday, UK)
1834	Lenz's law	lenz
1865	Maxwell's equations Established the electromagnetic theory, Predicted the electromagnetic wave	Maxwell
1888	Experiments confirm the existence of electromagnetic waves	Heinrich Hertz (Hertz, Germany)
1896	Speed of light formula	Hendrik Anoen Lorentz Lorenz

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