Electricity isphysicsOne of the subdisciplines of.It mainly studies the formation and application of electricity.The term "electricity" in the West is derived fromGreek The word "amber" comes from the phenomenon of lightning flash in China.
Since the middle of the 18th century, the research on electricity has gradually flourished.Each of its major discoveries has led to extensive practical research, thus promoting the rapid development of science and technology.Nowadays, both human life, scientific and technological activities and material production activities are inseparable from electricity.With the development of science and technology, some research contents with specialized knowledge gradually become independent, forming specialized disciplines, such aselectronics、ElectrotechnicsEtc.Electricity can also be calledelectromagneticsIs of great significance in physicsBasic discipline。
Is to study the generation of static chargeselectric fieldAnd the law of the action of electric field on electric charge.There are only two kinds of charges, calledPositive and negative。The same kind of charges repel each other, and the different kinds of charges attract each other.Charge complianceLaw of conservation of charge。Charge can be transferred from one object to another, and the algebraic sum of charge remains unchanged in any physical process.The so-called electrification is just the separation or transfer of positive and negative charges;The so-called charge disappearance is just positive and negativechargeNeutralization of.
charge
Between static chargesInteraction forceConform to Coulomb's Law:vacuumMiddle two stationaryPoint chargeThe magnitude of the force between them is in direct proportion to the product of their charge amount, and inversely proportional to the square of the distance between them;The direction of the force is along the line between them,Electric charges with the same sign repel each other，Dissimilar charge attraction。
Common substances can be divided into two cases according to their different conductive properties:conductorandinsulator。There are movableFree charge；Insulators, also called dielectrics, have only bound charges in the body.
Electrical research has entered the scientific ranks
Under the action of electric field, the free charge in the conductor will move.When the composition and temperature of the conductor are uniform, static electricity is achievedbalanceThe condition is that the electric field strength inside the conductor is equal to zero everywhere.According to this condition, the conductor can be derivedElectrostatic balanceSome properties of.
Magnetostatics
It is to study the magnetic field generated when the current is stable and the effect of the magnetic field on the currentForceThe discipline of.
The directional flow of electric charges forms an electric current.There is a magnetic interaction between currents. This magnetic interaction is transmitted through the magnetic field, that is, the current generates a magnetic field in the space around it,magnetic fieldApply force to the current placed in it.For magnetic field generated by currentMagnetic inductionDescription.
electromagnetic field
Is to study the change ofelectromagnetismThe discipline of phenomena and laws.
When passing through a closed conductorcoilOfMagnetic fluxWhen changes occurinduced current。The direction of induced current can be determined byLenz's lawdetermine.The induced current in the closed coil is inducedemfThe result of promotion,Induced electromotive forcefollowFaradLaw: The magnitude of the induced electromotive force on the closed coil is always proportional to the time change rate of the magnetic flux passing through the coil.
maxwellequationGroup describes the general law of electromagnetic field.It is the same as the medium equation of matter, Lorentz force formula andLaw of conservation of chargeIn principle, it can solve all kinds of macro electrodynamic problems.
Electromagnetic theory
according toMaxwell's equationsAn important result of export is existenceelectromagnetic wave, the changing electromagnetic field propagates in the form of electromagnetic wave, and the propagation speed of electromagnetic wave in vacuum is equal tolight speed。This also shows that light is also a kind of electromagnetic wave, so the wave theory of light is included in the category of electromagnetic theory.
Circuit
DC equivalent circuit diagram
The DC circuit is connected by conductors (or wires), which have a certain resistance.Under stable conditions, the current does not change with time, and the electric field does not change with time.
According to the properties of electric field, basic conductive laws and the concept of electromotive force when it is stable, various practical laws of DC circuit can be derived:Ohm's law、Kirchhoff's law of circuit, and some effective and simple theorems for solving complex circuits:Equivalent source theorem, superposition theorem, reciprocity theoremDuality theoremThese practical laws and theorems form the theoretical basis of circuit calculation.
The electrical effect in matter is the link between electricity and other physical disciplines (even non physical disciplines).There are many kinds of electrical effects in matter, many of which have become or are gradually developing into specialized research fields.For example:
Electrostriction、Piezoelectric effect(MechanicalpressureElectricity and polarity produced on dielectric crystals) andInverse piezoelectric effect、Seebeck effect、Peltier effect(At the junction of two different metals or semiconductors, when the current passes in a certain direction, it emits heat, and when the current is reversed, it absorbs heat), Thomson effect (a metal conductor or semiconductor maintains a temperature gradient, when the current passes in a certain direction, it emits heat, and when the current is reversed, it absorbs heat)Thermistor(semiconductor material Medium resistance changes sensitively with temperature), photosensitive resistance (resistance in semiconductor materials changes sensitively with light)Photovoltaic effect(Semiconductor materials are generated by lightPotential difference）, etc.
The study of various electrical effects is helpful to understand the structure of matter and the basic processes occurring in matter. In addition, they also realize energy conversion and nonElectricityThe basis of electrical measurement.
Electromagnetic measurement
Einstein[1]
It is also a part of electricity.The development of measurement technology is closely related to the theoretical development of the discipline, which promotes the improvement of measurement technology;The improvement of measurement technology verifies the theory on a new basis and facilitates the discovery of new theories.
Electromagnetic measurement includes allelectromagneticsMeasurement of quantity and other relevant quantities (frequency and phase angle of alternating current, etc.).Various special instruments (ammeter, voltmeterOhmmeter, magnetometer, etc.) andmeasuring circuit They can be used to measure various electromagnetic quantities.
Another important aspect of electromagnetic measurement is non electric quantity (length, speeddeformation, force, temperaturelight intensity、componentEtc.).Its main principle is to convert the measurement of non electric quantity into the measurement of electromagnetic quantity by using some effect of the correlation between electromagnetic quantity and non electric quantity.Because electrical measurement has a series of advantages:AccuracyHigh, wide range, small inertia, easy to operate, remote telemetry and measurement technology automation can be realized, and non electric measurement is developing continuously.
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electricity and magnetism [1]
Electrical actionClassical physicsAs for its basic principle, a branch of the theory has been developed quite well, which can be used to explain various electromagnetic phenomena in the macro field.
In the 20th century, with the development of atomic physicsNuclear physicsWith the development of particle physics, human understanding has gone deep into the micro fieldElectromagnetic theoryrun into a stone wall.Although classical theory has given some useful results, many phenomena cannot be explained by classical theory.The limitation of the classical theory is that the description of charged particles ignores their wave characteristics, while the description of electromagnetic waves ignores theirParticle propertyaspect.
according toquantumFrom the point of view of physics, both material particles and electromagnetic fields have the characteristics of both particles and waves.staymicrocosmicDriven by physical research, classical electromagnetic theory has developed into quantum electromagnetic theory.
ancientSeven Sages One of them is namedThalesThe philosopher of.Around 600 BC, Thales saw that the Greeks at that time attracted feathers by rubbing amber and iron flakes by using magnetite, and he once thought about the reasons.It is said that his explanation is: "All things have spirit. Magnetism attracts iron, so magnetism has spirit." The "magnetism" here is magnetite ore.The Greeks called amber "elektron" (synonymous with English "electricity").
In the East, according to《Lu's Spring and Autumn Period》It is recorded in a book that China was made of magnetite during the Warring States PeriodcompassIn ancient times, they used the magnetic needle of the compass to identify directions.
Magnetic and electrostatic
1. Magnetism and static electricity
so calledFriction electrificationIn BC, people only knew it was a phenomenon.For a long time, there has been no progress in understanding this phenomenon.
Faraday, the father of electricity
The compass has been used in navigation since the 13th Sutra.At that time, compass put needle shaped magnetite ore in straw to make it float on the water.At the beginning of the 14th century, it was made into a rope handlemagnetic needleHanging navigation compass.
suchcompassIn 1492ColumbusThe discovery of the New World of America and the year 1519MagellanIt played an important role in discovering the route around the earth.
2. Thunder and static electricity
In BC China, thunder was considered an act of God.Said there were five companiesthunderIts elder is called Lei Zu. Under Lei Zu are Lei Gong and Dian Mu.Thunder is the thunder gong beating a big drum in the sky, and lightning is the lightning mother shooting light to the lower boundary with two mirrors.
here we areAristotleThe times have been more scientific.It is believed that the occurrence of thunder is due to the rise of water vapor on the earthThunderstorm cloudThunderstorm clouds condense when encountering cold air and become thunderstorms, accompanied by strong light.
It was in 1708 that Wall, an Englishman, thought that thunder was caused by static electricity.In 1748, Franklin designedLightning arrester。
The real beginning of electricity
In 1600, British physicist Gilbert found that not only amber and coal jade can attract small and light objects after friction, but also quite a number of substances can attract small and light objects after friction. He noticed that these substances do not have the north-south nature of magnets after friction.In order to show the difference from magnetism, he used the Greek alphabet pinyin of amber to call this property "electric".Gibb made the first one during the experimentElectroscopeThis is a fixed and rotatable metal rod in the center. When it is close to the rubbed amber, the metal rod can rotate and point to the amber.
In about 1660, Gelick of Madburg, Germany, invented the first friction motor.He made a rotatable sphere shaped like a globe with sulfur, and rubbed the rotatable sphere with his dry palm to get electricity.Galick's friction lifting motor has been continuously improvedstatic electricityIt played an important role in experimental research until the 19th century when Holtz and Tupler respectively inventedInduction motorWas replaced later.
In the 18th century, the study of electricity developed rapidly.In 1729, Gray in England found the difference between conductor and insulator when he studied whether the electric effect of amber could be transmitted to other objects: metal could conduct electricity, silk could not, and he charged the human body for the first time.Gray's experiment attracted the attention of Duffy in France.In 1733, Duffy found that insulated metal can also be electrified by friction, so he concluded that all objects can be electrified by friction.He called the electricity generated on the glass "glass", and the electricity generated on the amber is the same as that generated on the resin, which is called "resin".He got: objects with the same electricity repel each other;Objects with different electricity attract each other.
In 1745, Mushenbrook of Leiden, the Netherlands, invented the Leiden bottle that can save electricity.Leiden bottleThe invention of.
At about the same time, Franklin of the United States did a lot of meaningful work to enrich people's understanding of electricity.In 1747, he proposed based on experiments that electricity is an element that exists in all substances in a certain amount under normal conditions;Like fluid, electricity can be transferred from one object to another by friction, but it cannot be created;The total electric quantity of any isolated object is constant, which is usually calledLaw of conservation of charge。He called the excess part of the electricity obtained by the object during friction positive, and the part of the object that lost its electricity but was insufficient negative.
Strictly speaking, this unitary fluid theory of electricity seems incorrect, but his terms of positive and negative electricity were adopted, and he also observed that the tip of the conductor is easier to discharge.As early as 1749, he noticed many similarities between lightning flash and discharge. In 1752, he carried out lightning strike experiments by putting kites into clouds in thunderstorm weather, proving that lightning flash is a discharge phenomenon.The luckiest thing about this experimentFranklinUnexpectedly, he was not electrocuted because it was a dangerous experiment. Later, someone was electrocuted to death when repeating this experiment.Franklin also suggested that lightning rods should be used to protect buildings from lightning strikes, which was first realized by Davis in 1745, probably the first practical application of electricity.[1]
Franklin, thinking of storing electricity in Leiden bottle, made an experiment to put a kite into a thunderstorm cloud in June 1752.As a result, thunderstorm clouds are sometimes positively charged and sometimes negatively charged.thisKite Experiment Well known, many scientists are very interested in it and follow suit.In July 1753, Russian scientist Lehmann was killed by an electric shock in his experiment.
Through experiments with various metals,University of Pavia, ItalyProfessor Volta proved that zinc, lead, tin, iron, copper, silver, gold and graphite are metal voltage series. When two metals in this series contact each other, the metal belt in the front of the seriespositive electricityThe metal in the back row is negatively charged.He invented the voltaic battery by placing copper and zinc as two electrodes in dilute sulfuric acid.The unit of voltage "volt" is named after him.
At the beginning of the 19th century, it was after the French Revolution that the Napoleon era entered.Napoleon returned from Italy and summoned Volta to Paris in 1801 to do electrical experiments. Volta also won the gold medal and the Legino Donor medal awarded by Napoleon.
Voltaic batteryThe Application of GIS and the Development of Electromagnetism
After the invention of voltaic battery, various countries have carried out various experiments and researches with this battery.Germany carried out research on electrolytic water. David, a British chemist, connected 2000 voltaic batteries together and carried outelectric arcDischarge test.David's experiment is to install charcoal on the positive and negative electrodes, and adjust the distance between the electrodes to make them discharge and emit strong light, which is the beginning of electricity used for lighting.
1820, DenmarkUniversity of CopenhagenProfessor Oster published his discovery in a paper: put a magnetic needle beside the wire connected to the voltaic battery, and the magnetic needle will deflect immediately.
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Sillinger of Russia read this paper, and he put the coil andmagnetic needleCombined, inventedTelegraph(1831), which can be said to be the beginning of the telegraph.
Later, the French ampere discovered the direction of the magnetic field generated around the currentAmpere's law(1820),FaradayHas discovered the epoch-makingElectromagnetic induction phenomenon(1831), electromagnetism developed rapidly.
On the other hand, the research on circuit is also developing.Ohm found out about resistanceOhm's law(1826),KirchhoffThe law of circuit network was discovered (1849), which established electrotechnics.
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wire communication
The history of wired communication
Some people say that science and technology are developed due to military needs, which has some historical facts.
Britain was afraid of Napoleon's attack and used truss communicators to report the French army's movements to its troops.Sweden, Germany, Russia and other countries have also set up communication networks composed of such communication machines for military purposes, and it is said that they have all invested huge budgets.
The idea of transforming this communication machine into an electrical communication mode is probably the beginning of wired communication.
1. Principle of wired communication
Electrical Experiment
In addition to the electromagnetic telegraph invented by Schilling mentioned above, there are also the electrochemical telegraph invented by Jan Merlin of Germany, the telegraph invented by Gauss and Weber (Germany), and the 5-pin telegraph invented by Cook and Wesnel (Britain).Telegraph machines come in various forms, including sound, printing, pointer, bell and bell, etc.Among them, Cook and Wheatstone's 5-pin telegraph is the most famous.In 1837, this kind of telegraph machine was put into practical use through five wires that were 20 kilometers long between London and West Drayton.
2．Morse telegraph
In 1837, Morse telegraph was successfully developed in the United StatesMorse codeAnd Morse is famous.Morse code is a signal encoded by dots and dashes.
Dictionary of electrocardiology
Morse originally wanted to be a painter, for which he studied in London.In 1815, he heard a talk about telegraph from Professor Jackson of Boston University on the ship returning to the United States, and conceived the idea of Morse code and telegraph machine.In order to lay telegraph lines, Morse founded the Electromagnetic Telegraph Company, and opened telegraph services between New York Boston, Philadelphia Pittsburgh, Toronto Buffalo New York in 1846.
Morse's career was a great success, so he set up telegraph companies all over the United States, and the telegraph business gradually expanded.
In 1846, Morse telegraph was equipped with an audio receiver, which was more convenient to use.
On February 14, 1876, Bell and Gray, two American inventors, respectively submitted applications for telephone patents. Bell's application arrived two hours earlier than Gray's application, so Bell obtained the patent right.
In 1878, Bell set up a telephone company to manufacture telephones and devote himself to the development of the telephone industry.
Since the development of telephone service, the switch has been shouldering an important task.The switch around 1877 was called the ticket type switch. When the operator received the call request, he handed the ticket to another operator.
Later, after repeated improvements, the block diagram switch was developed, and then the automatic switching mode was developed (1879).
In 1891, Strowger automatic exchange was successfully developed.At this point, the wish of automatic exchange is realized.After that, the research continued, and it took several stages to reach the electronic switch on the market today.
4. Submarine communication cable
With the gradual completion of the land communication network, people began to consider laying communication cables on the seabed to achieve communication between cross sea countries.Around 1840, Wheatstone had considered the problem of submarine cables.
There are many problems to be solved for submarine cables. The mechanical strength, insulation and laying methods of cables are different for onshore cables.
In 1845, the Channel Submarine Telegraph Company was founded, and began the submarine cable laying project from Britain to Canada and across the Dover Strait to France.
The laying of submarine cables has encountered major problems such as cable breakage, but the laying of submarine cables is a requirement of the times, and all countries have contributed to it.
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In 1851, the earliest Calais Dover submarine cable was laid and communication was successfully realized.Taking this opportunity, many cables have also been laid around Europe and the eastern Americas.
Today, the world's oceans are covered with cables for communication.
wireless communication
History of wireless communication
The information of any region in the world can be displayed on TV, which is convenient because of radio waves.
originalair wavesThe experiment was carried out by Hertz of Germany in 1888.Through experiments, Hertz found out that radio waves, like light, have linear propagation, reflection andrefractionPhenomenon.
The unit of frequency, Hertz, comes from his name.
I read it in a magazineHertz experimentMarconi, the Italian of the article, developed the earliest radio device in 1895, and used this device to carry out the test at a distance of about 3 kilometersMorse codeCommunication experiment.He thought of turning wireless communication into an enterprise, and set up a wireless telegraph and signal company.
Although Marconi had achieved many successes in the field of wireless communication, his intention to set up a wireless telegraph office in Newfoundland was opposed due to the conflict of interests with the submarine cable company. Marconi's opponents were not few.
Dadel uses a circuit composed of coils and capacitors to generate a high-frequency signal, but the frequency is less than 50KHZ, and the current is only 2-3 A, which is relatively small.
In 1903, Balusen in the Netherlands usedalcoholsteamArc dischargeThe high frequency wave of 1MHZ was generated, and Peterson improved it to make a device with an output power of 1KW.
Later, Germany designed a mechanical high-frequency generator. Stella and Fessenden of the United States, Goldschmidt of Germany and others developed the method of generating high-frequency waves with high-frequency AC machines. Many scientists and engineers have been committed to the research of high-frequency wave generators.
3. Wireless telephone
If the transmission is not Morse signal but human language, then there needs to be a carrier carrying the signal.The carrier wave must be high frequency wave.
In 1906,GE(GE)'s Alexandrson has made a 80KHZ high-frequency signal generator, and successfully conducted the wireless telephone experiment for the first time.
To transmit voice by wireless telephone and listen to it, it requires a high-frequency signal generator for transmission and a detector for reception.Fessenden designed a multi difference receiver, which was successfully tested in 1913.
Dadel designed a receiver mode in which the Balusen arc transmitter is the transmitting device and the electrolytic detector is the receiving device.At that time, because sparks were usedoscillator, so the noise is very big. The experiment phase can be said to be successful, but it is far from practical use.
If you want to make the generated radio waves stable and the received noise low, you have to waitElectronic tubeThe occurrence of.
4. Diode and triode
In 1903, Edison found that the electrons splashed from the hot filament of the light bulb blackened part of the light bulb. This phenomenon is calledEdison effect。
In 1904, Fleming was inspired by the Edison effect and built a diode to detect waves.
In 1907, D.Forrest in diodeanodeandcathodeAn electrode called grid was added between them, andtriode。
This triode can not only be used to amplify signal voltage, but also be matched with appropriate feedback circuit to generate stable high-frequency signal, which can be said to be an epoch-making circuit element.
After further improvement, the triode can generate high-frequency signals such as short wave and ultrashort wave.In addition, the triode has the function of controlling the electron flowcrtandOscilloscopeIt is closely related to this.
5. Battery history
In 1790, Gavani put forward "animal electricity" based on the experiment of dissecting frogs. From this point, Volta discovered the rule that electricity is generated when two metals contact, which can be said to be the origin of batteries.
In 1799, Volta sandwiched a layer of paper saturated with salt water between copper and zinc, and then stacked them layer by layer to make“Voltaic stack”。"Battery stack" means to stack many single battery cells together.
(1) Primary battery
The battery that can not be reused after the primary battery is discharged is called the primary battery.Volta battery is made by improving the Volta stack.
In 1836, Daniel, an Englishman, put anode and oxidant into a ceramic bucket to make Daniel battery.Compared with voltaic battery, Daniel battery can supply current for a long time.
In 1868, France's Leclanche announced the Leclanche battery, and in 1885 (Meiji 18), Japan's Seizo Uei invented the dry battery.Tailwell dry battery is a special battery that adsorbs electrolyte in sponge, which is easy to handle.
In 1917, Ferry of France invented the air battery, and in 1940, Rubin of the United States invented the mercury battery.
(2) Secondary battery
The battery that can be recharged after discharging is called secondary battery.In 1859, Francois Plante invented a lead battery that can be recharged repeatedly. Its structure is that dilute sulfuric acid contains lead electrodes, which is the earliest secondary battery.Today, this type of battery is used in cars.
In 1897 (the 30th year of Meiji era), Shimadzu Yuanzang of Japan developed a lead-acid battery with a capacity of 10A * H, and put his own name GS, GENZO SIMAZU, as a trade name, on the market as GS battery.
In 1899, Sweden made the storage battery, and in 1905 Edison made the Edison battery.The electrolyte of these batteries isPotassium hydroxide, later called alkaline battery.
In 1948, Newman of the United States invented the nickel cadmium battery.This is a rechargeable dry battery, which is of epoch-making significance.
In 1939, Grove, an Englishman, found that there wereelectric energyThe possibility of fuel cell is proved by experiments.That is to say, when electrolyzing water, electricity is consumed and oxygen and hydrogen are generated. In turn, electricity and water can be generated by feeding oxygen to the anode side and hydrogen to the cathode side from the outside.
Grove only did experiments at that time, not practical.In 1958, Cambridge University (UK) made a 5KW fuel cell.
In 1965, GE successfully developed a fuel cell, which was installed on the manned spacecraft Gemini 5 in 1965 and used to supply astronauts with power for drinking water.The Apollo 11 spacecraft that landed on the moon in 1969 also used fuel cells as the power supply inside the spacecraft.
In 1873, Siemens, a German, invented thephotoelectricityPool.This kind of selenium photocell is used in the new camera exposure meter.
In 1945, the American Xiapin inventedSilicon solar cell, which is a component that can generate electric energy when sunlight or light shines on its PN junction, and is widely used in artificial satellites,Solar cars, clock, desktopCalculatorEtc.The research and development work to improve the conversion efficiency of such components is still in progress.
6. History of lighting
The industrial revolution that arose in Britain in the 1860s brought factories into the era of continuous processing and mass production, and night lighting became an important issue.
As mentioned earlier, David, an Englishman, once conducted a famous experiment in 1815 to generate an arc with 2000 voltaic batteries.
(1) Incandescent bulb
In 1860, an Englishman Swan carbonized cotton thread to make a filament and put it into a glass bulb, and invented the carbon filament bulb.
However, due to theVacuum technologyNot high. The lighting time cannot be too long. As time goes on, the filament will oxidize in the bulb and burn off.
The principle of incandescent bulb that Swan thought of is the origin of incandescent lamps on the market today.With the development of filament research and vacuum technology, incandescent lamps have finally reached practical application.From this point of view, Swan's invention is a great invention.
In 1865, Sprunger developed the mercury vacuum pump to study the vacuum phenomenon.After Swan knew this, he put thevacuum degreeImprove, and work hard on the filament.He first treated the cotton thread with sulfuric acid, then carbonized it. Finally, he announced the Swan light bulb.Swan's incandescent bulb was once in ParisWorld ExpositionOn display.
In 1879, Edison of the United States successfully extended the life of incandescent bulbs to more than 40 hours.In 1880, Edison discovered that bamboo was an excellent material for making incandescent lamp filaments. He collected bamboo from Japan, China, and India for repeated experiments.
Edison sent Mur, his subordinate, to Japan to look for high-quality bamboo in Bafan, Kyoto. Several years later, he made a filament out of Bafan bamboo.In order to manufacture this kind of bamboo filament light bulb, he founded Edison Electric Light Company in London and New York in 1882.
In Japan, the Tokyo Electric Light Company was founded in 1886 (Meiji 19). Since Meiji 22, ordinary families began to use incandescent bulbs.
In 1910, Cooley Hall of the United States invented the tungsten filament bulb with tungsten filament as the filament.
In 1913, American Lamir filled the glass shell with gas to prevent the filament from evaporating, and invented the gas filled tungsten filament bulb.
In 1925, Japan's Bukusan invented the frosted bulb on the inner wall.
In 1932, Shunichi Miura of Japan invented the double helix tungsten filament bulb.
It is because of the above continuous exploration that we can enjoy the daily life of incandescent lighting. It's a long way to think of it.
(2) Discharge lamp
In 1902, Hewitt of the United States filled the glass shell with mercury vapor and inventedArc dischargeMercury lamp.Because this mercury lamp emits more ultraviolet rays when the pressure of mercury vapor is low, it is often used as a sterilization lamp.When the mercury pressure is high, it can emit strongvisible light。
The light emitted by the high-pressure mercury lamp, which is widely used for square lighting and road lighting, is a kind of mixed light. The mixed light includes the light from mercury arc discharge and ultraviolet light on the inner wall of the glass shellFluorescent materialThe light from the.
In 1932, Philips of the Netherlands developed a 590nm monochrome sodium lamp, which is widely used for tunnel lighting of roads.
Inman of the United States invented the widely used fluorescent lamp in 1938.This kind of lamp is coated on the inner wall of the lamp by ultraviolet radiation emitted by mercury arc dischargePhosphorAnd emit light of different colors.Generally, white fluorescent lamps are used most.
7. History of power equipment
It can be said that the electromagnetic effect discovered by Oster in 1820 is the origin of motor.
The electromagnetic induction discovered by Faraday in 1831 is the origin of the generator transformer.
(1) Generator
In 1832, the French Bixie invented the hand-operated typeDC generator, which is based on the principle ofturnPermanent magnetfluxChange occurs in the coilInduced electromotive forceAnd output this electromotive force in the form of DC voltage.
In 1866, Siemens of Germany invented the self-excited DC generator.
In 1869, Gram of Belgium made the ring armature and invented the ring armature generator.This kind of generator uses water power to rotate the generator rotor. After repeated improvement, 3.2KWoutput power。
In 1882, Gordon of the United States produced a two-phase giant generator with output power of 447KW, height of 3m and weight of 22t.
Tesla of the United States has been determined to developalternating current dynamoHowever, Edison insisted on DC only, so he put twoalternatorAnd the patent rights of the motor were sold to Westinghouse.
In 1896, Tesla's two-phase alternator started working in Nyala Power Plant, and 3750KW, 5000V AC power was sent to Buffalo 40 kilometers away.
In 1889, Westinghouse built a power plant in Oregon, and successfully delivered 15000 volts to Pittsfield in 1892.
(2) Motor
In 1834, Russia's Jacobi trial producedelectromagnetConstitutiveDC motor。In 1838, this kind of motor started a ship, and the power supply of the motor used 320 batteries.In addition, Winport in the United States and Debbie Wilson in England also created a DC motor (1836), which was used as the power equipment of the printing press.Because these motors are powered by batteries, they are not widely used.
In 1887, the previously mentioned Tesla two-phase motor was appliedinduction motor The development plan of started.In 1897, Westinghouse made induction motor, and established a professional company dedicated to the popularization of motor.
When the power generation terminal transmits AC power, it should first increase the AC voltage, and then reduce the AC voltage when it reaches the power consumption terminal.Therefore, transformer is indispensable.
In 1831, Faraday discovered that magnetism can induce electricity, which is the basis of the birth of transformers.
In 1882, Britain's Gibbs obtained the patent of "power distribution mode for lighting and power", which was to use transformers for power distribution. The transformers used at that time weremagnetic circuitOpen type transformer.
Westinghouse introduced Gibbs' transformer and developed a practical transformer in 1885 after research.
In addition, the year before that, in 1884, Hopkinson in England made a closed magnetic circuit transformer.
(4) Power equipment and three-phase AC technology
Two phase alternating current is a technology that uses four wires to transmit electricity.Dobrowski of Germany came up with a trick on the winding, leading out taps from three places every 120 degrees on the winding, and gotThree phase alternating current。In 1889Rotating magnetic fieldThe earliest three-phase AC motor with power of 100W has been made.
In the same year, Dobrowski developed the three-phase four wire AC connection mode, which was successfully achieved in the Frankfurt transmission experiment (150VA three-phase transformer) in 1891.
8. History of electronic circuit components
The contemporary era is a prosperous era of electronics, including computers. Its background and electronic circuit components consist of electronic tubes and transistors=Integrated circuitThe continuous development of is closely related.
The electron tube is along the diode triode tetrode-PentodeThe order of invention.
Diode: As mentioned earlier, Edison discovered that the light bulb filament emits electrons“Edison effect”。In 1904, Fleming, an Englishman, was inspired by the Edison Effect and invented the diode.
Triode: In 1907, American Forrest invented the transistor.At that time, the vacuum technology was not yet mature, and the manufacturing level of triodes was not high.However, in the process of repeated improvement, people learned that the triode has the role of amplification, and finally opened the curtain of electronics.
Oscillator also developed from Marconi spark device mentioned above to triode oscillator.The triode has three electrodes,anode，cathodeAnd a control grid arranged between the two, which is used to control the electron flow emitted by the cathode.
Quadrode: In 1915, the British Lande added an electrode between the control grid and anode of the triode, called the curtain grid, to solve the problem that part of the electron flow from the triode to the anode will flow to the control grid.
Pentode: In 1927, Jobst in Germany added an electrode between the anode and the screen grid, and invented the pentode.The new electrode is called the suppression gate.The reason for adding this electrode is that in the tetrode, the electron stream collides withanodeAnode will be generated when it is upSecondary electronEmission and suppression gate are set to suppress such secondary electron emission.
In addition, in 1934, through the miniaturization of the electronic tube, Thompson of the United States invented the rubber tube suitable for ultrashort wave.
ST tube with metal shell instead of glass was invented in 1937, and MT tube after miniaturization was invented in 1939.
Semiconductor devices can be roughly divided into transistors and integrated circuits (ICs).the Second World WarLater, due to the progress of semiconductor technology, electronics has made remarkable progress.
Transistors areBell Lab It was invented by Shockley, Bardeen and Blatter in 1948.
The structure of this transistor is to make two metal wires and low dopingGermanium semiconductorSurface contact is called contact transistor.
In 1949, the junction transistor was developed, which made a great progress in practical application.
In 1956, it developed thespreadLaw.It is a method of penetrating impurity atoms into the surface of semiconductor at high temperature.Developed in 1960epitaxial growth The epitaxial planar transistor was fabricated.Epitaxial growth method is to place silicon crystal in hydrogen andhalideA method of making semiconductors in gases.
With the development of semiconductor technology, integrated circuits came into being.
About 1956, Britain's Dama predicted the emergence of integrated circuits from the principle of transistors.
In 1958, the United States proposed to manufacture all circuit components with semiconductors to realize integrated circuit.
In 1961, Texas Instruments began mass production of integrated circuits.
The integrated circuit is not a circuit connected by a circuit component, but a device that embeds a circuit with a certain function in a semiconductor crystal.It is easy to miniaturize and reduce the lead end, so it has the advantage of high reliability.
The integration of integrated circuits is increasing year by year.The number of components is less than 100Small scale integrated circuit, 100~1000Medium scale integrated circuit, 1000~100000 large-scale integrated circuits, and more than 100000vlsi, which have been successively developed and widely used in various devices.
Junior high school circuit knowledge
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Basic circuit
Current generation:positive chargeThe directional movement of creates a current.
conductorObjects that are easy to conduct electricity are called conductors
Insulator: objects that are not easy to conduct electricity are called insulators.
The circuit has three states: (1) path: the connected circuit is called path;(2)open circuit: The disconnected circuit is called open circuit, also called open circuit;(3) Short circuit: The circuit that connects the wire directly to the two poles of the power supply is called short circuit.
Series connection:elementConnecting them one by one is called series connection.(If it is disconnected at any place, the current will disappear)
Parallel connection: connect components in parallel, called parallel connection.(Each branch does not affect each other)
The instruments for measuring current are:ammeterIts use rules are: ① the ammeter should be connected in series in the circuit; ②The current shall enter from the "+" terminal and exit from the "-" terminal; ③The measured current shall not exceed the range of the ammeter; ④It is absolutely not allowed to connect the ammeter to the two poles of the power supply without using electrical appliances.
Voltage
International unit: volt (V);Commonly used: kilovolt (KV), millivolt (mV). 1 kilovolt=1000 volts=1000 000 millivolts.
The instrument for measuring voltage is a voltmeter. The rules of use are: ① The voltmeter should be connected in parallel in the circuit; ②The current shall enter from the "+" terminal and exit from the "-" terminal; ③The measured voltage shall not exceed the range of the voltmeter;
Remembered voltage value: ① 1.5 V for 1 dry cell; ②The voltage of one lead-acid battery is 2V; ③The home lighting voltage is 220 V; ④Safety voltage: no more than 36V; ⑤The industrial voltage is 380 V.
resistance
Resistance (R): refers to the resistance between conductor and currentHindrance。(The greater the resistance of the conductor to the current, the smaller the current through the conductor)
Principle: changeResistance wireThe length in the circuit changes the resistance.
Function: Change the current and voltage in the circuit by changing the resistance in the incoming circuit.
Nameplate: if a sliding rheostat is marked with "50 Ω 2A", it means that the maximum resistance is 50 Ω and the maximum allowable current is 2A
Correct use: a. It should be used in series in the circuit;b,Wiring shall be "up and down";c,Before power on, the resistance should be adjusted to the maximum.
Ohm's law
Ohm's law：conductorThe current in is proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor.
Formula:
Where unit:
→ A;
→ Volts (V);
→ Ohms
Understanding of formula: ①
,
and
It must be in the same section of circuit; ②
,
and
If any two quantities are known in, the other quantity can be obtained; ③The calculation unit shall be unified.
Application of Ohm's Law:
① The resistance value of the same resistance is unchanged, independent of current and voltage, and its current increases with the increase of voltage.(
)
② When the voltage is constant, the greater the resistance, the smaller the current will pass through.(
)
③ When the current is constant, the greater the resistance, the greater the voltage at both ends of the resistance(
)
The series connection of resistors has the following characteristics:
，
In series, the more series, the greater the resistance)
(The total voltage is equal to the sum of all voltages)
③ Resistance:
(The total resistance is equal to the sum of all resistances) If n equivalent resistances are connected in series, then R total=nR
④ Partial pressure action:=;calculation
,
, available:
；
The parallel connection of resistors has the following characteristics: (It means that R1 and R2 are connected in parallel, and the more the parallel connection, the smaller the resistance)
① Current:
(The main circuit current is equal to the sum of the branch currents)
② Voltage:
(Main circuit voltage is equal to each branch circuit voltage)
③ Resistance: (the reciprocal of the total resistance is equal to the reciprocal sum of each resistance) 1/R total=1/R1+1/R2+1/R3++1/Rn
④ Divergence:;Calculate I1, I2 available:;
⑤ Proportional relation: voltage: U1: U2=1:1, (Q is heat)
Electric work and power
1．Electric power(W) The amount of electric energy converted into other forms of energy is called electric power,
2. SI unit of work:joule. Common: degrees（Kilowatt1 degree=1 kilowatt hour=3.6 × 10 ^ 6 joules.
4. Electric work formula: W=Pt=UIt (unit in the formula: W → focal (J);U → V;I → A;T → seconds)
When using W=UIt to calculate, pay attention to: ① WU. I and t are in the same section of the circuit; ②The unit shall be unified during calculation; ③The fourth quantity can be obtained when any three quantities are known.There is also the formula:=I2Rt
Formula: the unit in the formula is P → watt (w);W → coke;T → s;U → V, I → A
The unit of calculation shall be unified. ① If W is in focus and t is in seconds, then P is in watt; ②If W is in kilowatt hours and t is in hours, then P is in kilowatts.
10. The right formula can also be used to calculate electric power:
and
11. Rated voltage (U0): the voltage at which electrical appliances work normally.In addition: rated current
12. Rated power (P0): the power of electrical appliances at rated voltage.
13. Actual voltage (U): the voltage actually applied to both ends of the consumer.In addition: actual current
14．Actual power(P) : The power of the consumer under the actual voltage.
When
When, then
;The lamp is very bright and easy to burn out
When
When, then
;The light is dim,
When
When, then
;Normal lighting.
15. If the same resistance is connected to different voltages, there is;For example, when the actual voltage is half of the rated voltage, the actual power is 1/4 of the rated power. For example, if "220V100W" is connected to a 110 volt circuit, the actual power is 25 watts.
16. Thermal power: the thermal power of conductor is proportional to the square of current and the resistance of conductor.
17. P Thermal formula:
, (where the unit is P → W);I → A;R → Ω;T → s)
18. When the current passes through the conductor, all the work (electric work) is used to generate heat（electrothermal）, then there is: thermal power=electric power, and the thermal power can be calculated by the electric power formula.(For example, the resistance of electric heater is like this.)
Domestic electricity
Home circuit: incoming line (live line and neutral line) → electricity meter → main switch → fuse box → electrical appliance.
All household appliances and sockets areparallel connectionThe electrical appliance should be connected with its switch stringLive wire。
Fuse: YesresistivityLarge, low melting pointLead antimony alloymake.Its function is that when there is too much current in the circuit, it will fuse when the temperature rises to the melting point, automatically cut off the circuit and play the role of insurance.
There are two reasons for the excessive current of the circuit: one is the short circuit of the circuit;Second, the total power of electrical appliances is too large
The principles for safe use of electricity are: ① Do not contact low voltageCharged body；②Not close to high-voltage charged body.
Electricity and magnetism
Magnetism: The property that objects attract iron, nickel, cobalt and other substances.
magnet: Objects with magnetism are called magnets.It hasDirectivity: Refers to the north and south
magnetic pole: The strongest part of the magnet is called the magnetic pole.
Any magnet has two magnetic poles, one is the North Pole (N pole);The other is South Pole (S Pole)
Role between magnetic poles: homonymous magnetic poles repel each other, and synonymous magnetic poles attract each other.
magnetization: The process of making a previously nonmagnetic object magnetic.
There is a magnetic field around the magnet, and the interaction between the magnetic poles occurs through the magnetic field
Basic property of magnetic field: generated by magnetsmagnetic forceRole of.
Direction of magnetic field: smallmagnetic needleThe direction of the North Pole at rest is the direction of the magnetic field at that point.
Magnetic induction line: an imaginary curve describing the strength and direction of the magnetic field.It does not exist and does not intersect. It goes out from north to south
The direction of the magnetic field at a certain point in the magnetic field, the direction of the magnetic induction line, and the direction of the north pole when the small magnetic needle is stationary are the same.
The north pole of the geomagnetic field is near the south pole of the geographical position;The south pole of the geomagnetic field is near the geographical north pole.But they do not coincide. Their intersection angle is calledMagnetic declinationShen Kuo, a Chinese scholar, first described this phenomenon.
Ampere rule: Right hand gripsolenoidLet the four fingers bend to the current direction in the solenoid, then the end of the thumb is the north pole (N pole) of the solenoid
Energized solenoidProperties of: ① The greater the passing current, the stronger the magnetism; ②Turn Ratio The more, the stronger the magnetism; ③Insert soft iron core to greatly enhance the magnetism; ④The polarity of the energized solenoid can be changed by the current direction.
Electromagnet: A solenoid with an iron core inside constitutes an electromagnet.
Features of electromagnet: ① whether the magnetism is available or not can be controlled by current on-off; ②The strength of magnetism can be adjusted by changing the current and the number of turns of the coil; ③The magnetic pole can be changed by the current direction.
electromagnetic relay In essence, it is a switch controlled by electromagnet.Its function can realize remote operation, using low voltage and weak current to control high voltage and strong current.It can also realize automatic control.
Basic principle of telephone: vibration → strong and weak current → vibration.
Electromagnetic induction: part of the conductor in the closed circuit is conducted in the magnetic fieldCutting magnetic induction line movementThe current generated in the conductor is called electromagnetic induction, and the current generated is calledinduced current。Application: Generator
Conditions for induced current: ① the circuit must be closed; ②Only part of the conductor of the circuit is in the magnetic field; ③This part of conductor moves by cutting magnetic induction line
Direction of induced current: it is related to the direction of conductor movement and the direction of magnetic induction line.
The effect of magnetic field on current: the electrified wire is subject to the effect of magnetic force in the magnetic field.It is the conversion of electrical energy into mechanical energy.Application: motor.
The force direction of the energized conductor in the magnetic field is related to the current direction and magnetic induction line direction
Motor principle
MotorIt is made by the principle that the electrified coil rotates under force in the magnetic field.
commutator: Realize the exchange between AC and DC.
alternating current: The current that periodically changes the direction of the current.
