Any current carryingwireway, can produce magnetic field around it, which is called the magnetic effect of current.Magnetic phenomenonAnd electrical phenomena are studied separately, especially Gilbert's assertion after in-depth analysis and comparison of magnetic and electrical phenomenaElectricity and magnetismThey are two completely different phenomena without any consistency.Later, many scientists believed that there was no connection between electricity and magnetism. Even Coulomb once asserted that electricity and magnetism were two completely different entities, and they could not interact or transform.But the question of whether there is a certain connection between electricity and magnetism has always haunted some scientists who are interested in exploring.
Danish physicist Hans·Oster(H.C. Oersted, 1777-1851) isKant Believers in philosophy are deeply influenced by Kant and others about the mutual transformation of various natural forcesPhilosophical thoughtOster firmly believed that various forces in the objective world have unity, and began to study the unity of electricity and magnetism.1751FranklinuseLeiden bottleThe discovery that the method of discharge made the steel needle magnetized greatly inspired Oster. He realized that the transformation from electricity to magnetism was not an impossible problem, but a problem of how to achieve it. The condition of the transformation between electricity and magnetism was the key to the problem.At first, Oster speculated that if the diameter of the electrified wire was further reduced, the wire would glow. If the diameter was further reduced to a certain extent, a magnetic effect would occur.But Oster failed to find the transformation from electricity to magnetism along this path.Oster was not discouraged because of this. He kept experimenting and thinking. He analyzed the magnetic effect of previous experiments that looked for current in the direction of current, and the results were all invalidmagnetIts role is not vertical at all, but a kind of lateral force, so Auster continued to explore new.One evening in April 1820, when Aust was giving a lecture to scholars who were proficient in philosophy and had considerable physical knowledge, he suddenly got "inspiration". At the end of the lecture, he said, "Let me connect the electrified wire with themagnetic needleTry it in parallel! "So, he connected a thin platinum wire between the two poles of a small Gavani battery, placed a magnetic needle directly below the platinum wire, and then connected the power supply. The small magnetic needle slightly jumped and turned to the direction perpendicular to the platinum wire.The swing of the small magnetic needle was nothing to the audience, but it was too important for Oster. He finally saw the phenomenon he had been looking forward to for many years. At that time, he was stunned. He changed the direction of the current and found that the small magnetic needle deflected in the opposite direction, indicating that there was some connection between the direction of the current and the rotation of the magnetic needle.
In order to further understand the effect of current on the magnetic needle, Oster spent three months from April to July 1820 to do more than 60 experiments. He placed the magnetic needle above and below the wire to investigate the direction of the effect of current on the magnetic needle;Put the magnetic needle at different distances from the conductor to investigate the effect of current on the magnetic needle;Put glass, metal, wood, stone, tile, turpentine, water, etc. between the magnetic needle and the wire to investigate the influence of current on the magnetic needle.On July 21, 1820, he published a paper entitled "Experiments on Current Collision on Magnetic Needle". This paper used only four pages to report his experiments very succinctly and announced the magnetic effect of current to the scientific community.July 21, 1820 was recorded in history as an epoch-making day, which opened the prelude to electromagnetism, markingelectromagneticsThe arrival of the times.
Oster then set the currentmagnetThe function of "current collision" is called "current collision". He summarized two characteristics: one is that the current collision exists around the current carrying wire;The second is the current collision "propagates along the thread direction perpendicular to the wire thread".Oersted experiment It confirmed the lateral effect of magnetic force generated by current. His belief established 20 years ago finally depends on his ownexperimentYes.
Some people say that Oster's current magnetic effect is "accidentally discovered the rotation of the magnetic needle", which is certainly reasonable, but the FrenchPasteurWell said: "In the field of observation, opportunities only prefer the prepared mind[1]。”
Ampere rule
Also called right-hand solenoid rule
Oster's discovery stirred the whole worldEurope, which shocked the French academic community in particular, French physicistArago staySwitzerlandHearing the news that Oster discovered the current magnetic effect, he was keenly aware of the importance of this achievement, and then rushed back to France from Switzerland in early September 1820.On September 11French Academy of SciencesHe reported this latest discovery of Oster and described the experiment of current magnetic effect in detail to his colleagues in the Academy of Sciences.Arago's report has aroused great repercussions among French scientists.At that time, A.M. Ampere (1775-1836), famous for his extreme sensitivity in science and his ability to accept the achievements of others, made an unusual response to this. He repeated Auster's experiment the next day and developed it. Within a week, he reported his first paper to the French Academy of Sciences on September 18, describing the current pair he repeatedmagnetic needleThe possibility of magnetic field produced by circular current is proposed.In this experiment, Ampere found that the relationship between the direction of rotation of the magnetic needle and the direction of current obeyed the right hand rule, which was called“Ampere right hand rule”。
Ampere's law
After that, Ampere creatively developed the experimental content and studied the effect of current on currentOersted experiment A big step forward.He also presented the second paper to the French Academy of Sciences, explaining that he proved by experiment that two parallel current carrying wires attract each other when the current direction is the same, and repel each other when the current direction is opposite.Later, Ampere studied the interaction between them by using curved current carrying wires of various shapes, and proposed the third paper.
After that, Ampere spent two or three months focusing on the interaction between currents.Ampere did four experiments by combining extremely ingenious experiments with quite superb mathematical skills.
In the first experiment, Ampere uses an astatic scale to check whether there is a folded electrified wireForceThe result is negative, which proves that when the current is reversed, it will produce the opposite effect.
In the second experiment, Ampere still used an undirected scale to test a pair of folded electrified wires, but at this time the other arm of the folded wire was wound into a spiral, and the result was also negative, thus proving that the current element has the vector property, that is, the cooperation of many current elements is equal to the vector sum of the actions produced by each single current element.
In the third experiment, Ampere designed a device, and the insulating handle fixed on the center of the circle at the same end was connected to a circular arcconductorThen, the circular arc conductor is placed on two energized mercury tanks. However, the circular arc conductor cannot move along its current direction as a result of the action of various energized coils on it.It is thus proved that the force acting on the current element is perpendicular to it.
In the fourth experiment, Ampere used three identical coils, 1.2 and 3. The linearity ratio of these three coils was consistent with the ratio of the three coils' spacing. After power on, it was found that the cooperation between coils 1, 3 and 2 was zero.This proves that eachCurrent intensityWhen the interaction distance increases by the same multiple, the force remains unchanged.
Ampere postulated thatInteraction forceAlong their lines, on this basis, Ampere summed up the formula that the force between the two current elements is inversely proportional to the square of the distance, which is famousAmpere's law。Ampere reported this extremely important achievement to the French Academy of Sciences on December 4 of the same year.
In order to explain the Oster effect, Ampere simplified the essence of magnetism as current, and believed thatmagnetThere is a magnetic axis windingPrecessionThe interaction between the current in the magnet and the current in the conductor leads to the rotation of the magnet.In a sense, it plays a role in unifying the interpretation of variousElectromagnetic phenomenonThe effect of.
butfresnelHe questioned Ampere's magnetic current. He believed that since there was current in the magnet, the magnet should have obvioustemperature riseHowever, it is impossible to measure the spontaneous heat release of the magnet.In this case, Ampere proposed the famousMolecular currentAssumptions:Magnetic materialEach molecule has a microscopic current, and the circular current of each molecule forms a small magnet.In magnetic materials, these currents are regularly arranged along the magnetic axis, which shows a current rotating around the magnetic axis, likesolenoidThe current is the same.In 1827, Ampere published the Theory of Electrodynamic Phenomena, which firmly established his mathematical theory of electrodynamics on the basis of the hypothesis of molecular current.
Other studies
Before ampere obtained the interaction formula of current elements, French scientists J.B. Biot (1774-1862) and F. Savart (1791-1841) obtained the pair of current carrying long straight wires through experimentsmagnetic poleRole ofinverse ratioAt the result of distance r, the French mathematician P.S. Laplace (1749-1827) used excellent mathematical analysis to help them raise the experimental results to a theoretical level, and came to the conclusion that Biot SavartLaplace's law(referred to as Bi Sa La law for short)magnetic field intensityIt is shown that the magnetic field intensity generated by the current element at a certain point in space is proportional toCurrent elementIs inversely proportional to the square of the distance from the current element to the point, and the direction of the magnetic field intensity isRight-Hand Rule Determine the distance perpendicular to the current element to the field point.
In memory of Auster
Oster's discovery reveals that electrical phenomena with different properties andMagnetic phenomenonAs a result, electromagnetism has entered a new period of development,FaradayLater, when evaluating this discovery, he said: "It suddenly opened the door of a scientific field, where it used to be dark, but now it is full of light." In memory of this learned scientist, people have named it "Oster" since 1934magnetic field intensityUnits of.
From July 1820OsterIt only took more than four months to publish the magnetic effect of current until December when ampere proposed ampere's law.However, electromagnetism has experienced a great leap from the summary of phenomena to the induction of theories, thus creating the theory of electrodynamics.These achievements not only reflect the strong insight of scientists as leaders of the times, but also a responsible founder of electromagnetism[2]。
concept
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definition
Magnetic effect of current (electricity will produce magnetism): Oster found that any current connectedwireway, can produce magnetic field around it, which is called the magnetic effect of current.
Non magnetic metal can generate magnetic field when it is connected with current, and its effect is the same as that of magnetic field established by magnet.
Magnetic field generated around long and straight conductors with current:
There will be a magnetic field around the long straight conductor with current. The shape of the magnetic induction line is a closed concentric circle with the conductor as the center, and the direction of the magnetic field is perpendicular to the direction of the current.
Right hand rule 1
Hold the wire with your right hand, with your thumb pointing in the direction of the current (so it must be direct current, the direction of the current, which is from the positive pole to the negative pole in the wire), and the other four fingers pointing in the direction of the magnetic force line or the direction of the magnetic force applied to the N pole of the magnetic needle.
Right hand rule 2
Hold the coil with your right hand and point the four fingers in the direction of the current on the wire, then the thumb is in the direction of the magnetic line of force.
Intensity of magnetic field 1
H (Gauss)=2I (ampere)/10r (centimeter)<==Long straight conductor
1: The total current on the guide line can be increased by increasing the number of turns of the coil.
r: Is the vertical distance from the wire.
*Note: The geomagnetic field is about 0.2 gauss.
Magnetic field intensity 2
Solenoid coil: pipe surface radius a, pipe length L, total coil turns N, P point X from the end face
a. Hollow: magnetic field of point X
b. If atsolenoidIt is filled with magnetic substances. In addition to the magnetic field generated by the original hollow coil, the magnetic field generated by magnetization of these substances must also be added, that is, the totalmagnetic field intensity(B) Expected
B=H+4πM=H+4πXH=（1+4πX）H=μH
10: Magnetic permeability M:MagnetizationH: Magnetic field of hollow coil
It can be seen from the above formula that the plug hasMagnetic materialThe magnetic field intensity generated by the solenoid is M times that of the hollow coil.commonlyFerromagnetic materialThe μ value of is between hundreds and tens of thousands.
Phenomenon of current magnetic effect
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When the horizontal current is directly above or below the small magnetic needle, and the current direction is along the north-south direction, the small magnetic needle will deflect significantly[3]。
