Ampere thinks that there is a kind of ring current in the molecule that makes up the magnet - molecular current.Due to the existence of molecular current, each magnetic molecule becomes a small magnet, and its two sides are equivalent to two magnetic poles.In general, the molecular current orientation of magnet molecules is disordered, and the magnetic fields generated by them cancel each other and are not magnetic to the outside.When the external magnetic field acts, the orientation of molecular current is roughly the same, and both ends show strong magnetic effect, forming magnetic poles, and then being magnetized.When the magnet is subjected to high temperature or violent impact, it will lose its magnetism, because the intense thermal movement or vibration makes the orientation of molecular current disorderly.
The molecular current hypothesis of Ampere is of great significance. On the one hand, it sums up the magnetic interaction between magnet and magnet, current and magnet, current and magnet, current and magnet and current as the action of current and current, establishes Ampere's law, and creates the theory of magnetic interaction that links electricity and magnetism;On the other hand, the substitution of the molecular current model for the magnetic charge model fundamentally reveals the internal relationship between material polarization and magnetization, because the molecular current is nothing more than a movement of charge.[1]
development
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AmperometricMolecular currentThe hypothesis could not be confirmed when there was little knowledge of the material structure at that time, and it had a considerable element of conjecture;It has been known today that substances are composed of molecules, while molecules are composed of atoms. There are electrons moving around the nucleus in atoms. From a modern point of view, "molecular current" is composed of the orbital motion of electrons around the nucleus, the spin motion of electrons, and the autorotation motion of the nucleus.Thus Ampere's molecular current hypothesis has a real content and has become an important basis for understanding the magnetism of matter.
The Formation of the Thought of "Molecular Current" -- "Trilogy"
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Throughout the history of physics books and related papers, although there is more or less discussion on the "molecular current" thought and its formation process, there is still a lack of clear clues. The author believes that the formation of Ampere's "molecular current" thought has experienced three cognitive leaps. Although the time between each step is not long, it can be described as a step by step, or a "trilogy"
Compared with other scientists, Ampere has a remarkable feature, that is, it is extremely sensitive in science and can most accept the achievements of others. This valuable quality determines that Ampere rather than others put forward the "molecular current hypothesis"
French physicist in early September 1820Arago (Framcois4rago, 1786-1853) brought back Danish physicists from SwitzerlandOster(Hans Christian Oersted, 1777-1851) The news of the discovery of the current magnetic effect immediately caused a huge response in the French scientific community. Ampere made an unusual response to this, and he repeated the experiment of the effect of Auster current on the magnetic needle the next day. During the experiment, Ampere gradually realized that magnetism is not an isolated phenomenon separated from electricity,But it is one aspect of many characteristics of electricity. He tried to explain the discovered electromagnetic phenomenon from the perspective of electricity. A week later, on September 18, he submitted his first paper to the French Academy of Sciences, reporting the results of his repeated Auster experiment, taking the first step to form his idea of molecular electrocurrent, and proposing that circular current has the possibility of acting as a magnet
Then, Ampere creatively developed the content of the experiment, studying the interaction between current and electric current, which was a step further than Auster's experiment. On September 25, he submitted the second paper to the French Academy of Sciences, stating that he used his experiment to prove that two parallel straight wires attract each other when the current direction is the same,When the direction of the current is opposite to the report of mutual exclusion, he later used various curved current carrying wires to study the interaction between them, and submitted the third paper on October 9, taking the second step to form the idea of molecular current, proposing that there is a macro current rotating around the magnetic axis in the magnet
In his paper, Ampere said: "When we consider the interaction between a current and a magnet, and the interaction between two magnets, we will find that these two situations will be governed by the same law. As long as a point on the straight line drawn from one pole to the other on the surface of the magnet has established a kind of rotation in the plane perpendicular to the magnetic axisAfter thinking about all the facts, we can hardly doubt the existence of this current around the magnetic axis. "
"In this way, the unexpected result is that the magnetic phenomenon is solely determined by electricity, and there is no difference between the two poles of a magnet except that they are relative to the current constituting the magnet. The magnetic south pole is to the right of these currents, and the magnetic north pole is to their left."
Ampere is a molecular theorist. His assumption that there is a macro current in his magnet is simply explained according to the principle of the Volta stack (Alessandro Volta, 1745-1827). He believes that the Volta battery can generate current because of the contact of different metals. Similarly,The contact of the iron molecules in the magnet will also produce current, that is, the magnet is regarded as a series of voltaic stacks, and their current moves in concentric circles around the axis of the magnet
Angustin Jean Fresnel (1788 ～ 1827) was a good friend of Ampere. After he learned Ampere's paper, he pointed out that the hypothesis of Ampere could not be tenable, that is, the magnet could not have the macroscopic current that Ampere had imagined, otherwise, the existence of macroscopic current would make the magnet generate heat,But in fact, the magnet cannot be warmer than the surrounding environment by itself. Fresnel suggested in a letter to Ampere, why not change the assumed macro current to surround every molecule?In this way, if these molecules can be arranged in rows, these microscopic currents will synthesize the required concentric currents
After receiving Fresnel's letter, Ampere immediately gave up the original assumption and adopted Fresnel's proposal. Around January 1821, he took the third step of the molecular current thought: proposed the famous "molecular current hypothesis", which profoundly reflected the essence of the magnetism of objects within the scope of classical physics
Ampere's explanation of his "molecular current hypothesis" is that the decomposition of the ether and the two current substances in each molecule inside the object will generate circular currents around the molecules, forming small magnets;When they are arranged regularly under the action of external magnetic field, the object presents macroscopic magnetism
It can be seen that the formation of the thought of "molecular current" has gone through three stages: "possibility", "macro current" and "molecular current", which is in line with the cognitive process of people from simple to deep, from the outside to the inside, and from phenomenon to essence. The "molecular current hypothesis" was proposed by Ampere, which is also inseparable from his unique scientific quality. Looking back at the age of Ampere,Especially after Auster discovered the magnetic effect of current, many scientists were engaged in the research of the connection between electricity and magnetism, such as Michael Faraday (1791-1867) in England, Jean Baptiste Biot (1774-1862) in France, and Thomas Johann Seebeck (1770-1831) in Germany,If Ampere did not repeat and develop Auster's experiment in time, if Ampere did not immediately accept Fresnel's suggestion, that is, if Ampere did not have the unique quality of being extremely sensitive in science and most able to accept the achievements of others, perhaps the proposer of the "molecular current hypothesis" would change[2]
Debates at the Initial Stage of "Molecular Current Hypothesis"
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According to the previous explanation of Ampere on the "molecular current hypothesis", it is difficult to accept. On this issue, Ampere was ahead of the times. Because at that time, people did not understand the structure of atoms, so they could not explain how the molecular current in matter was formed. Until 1911, Ernst Rutherford (1871-1937)Through the analysis and calculation of alpha particle scattering experiment, the concept of orbital magnetic moment came into being only after the model that all atoms have a nucleus and electrons rotate around the nucleus like planets was proposed. In 1922, Otto Steen (1888-1969) and W. Grelach successfully performed experiments with silver atoms, which were later named after their sons,It was found that there is a magnetic moment in the atom that cannot be explained by the orbital magnetic moment. In order to explain this problem, George Eugene Uhlenbeck (1900~) and Samuel Abraham Gondsmit (1902~1978) put forward the hypothesis that the electron has spin in 1925, successfully explaining the results of the Stern Gallagher experiment. Today we know that,It is these movements of electrons in atoms, molecules and other microscopic particles that form the "molecular current". But we cannot use the same level of physical development decades later to demand amperes, otherwise it will be too harsh,
After the "molecular current hypothesis" was put forward, although Ampere did not make further explanation, he was very firm in his belief. He inspired and suggested Arago to use an energized solenoid to conduct the experiment of magnetizing the steel needle in it. On September 25, 1820,Arago reported the results of the experiment to the French Academy of Sciences. The success of the experiment also strengthened the idea that the essence of Ampere's magnetism is electricity. In 1821, in response to a letter from the Dutch physicist Van Beck, he insisted that this hypothesis could not only be used to explain magnetic phenomena,It can also be used to explain chemical combination and chemical affinity. The latter became an important reason why his theory could not be immediately and generally accepted, because accepting this theory means accepting a new theory about the structure of matter. In addition, the molecular current model at that time was like a mist, so that people could not see it clearly. So the "molecular current hypothesis"Although it deeply reflected the essence of the magnetism of objects, it was rejected by most physicists at that time
Among the physicists who have raised objections to the "molecular current hypothesis", the most typical one is probably Faraday. In 1822, he designed an experiment: wrap an insulated wire on a glass tube to make a solenoid, which is half immersed in water horizontally. Then float a long magnetic needle on the water surface. According to Ampere's view, one end of the solenoid is equivalent to the magnetic South Pole,The other end is equivalent to the magnetic north pole. If the south pole of the magnetic needle points to the north pole of the solenoid, it should draw to the north pole of the solenoid and stop at the north pole end. Faraday pointed out that this is inconsistent with the experimental results. His experiment is that the south pole of the magnetic needle continues to pass through the solenoid until it is close to the south pole of the solenoid. Faraday argued that if the needle is unipolar,Faraday believed that what corresponds to the current carrying solenoid is not a solid magnet, but a cylindrical magnet
Ampere retorted that the cylindrical magnet is different from the solenoid. According to its molecular current hypothesis, the current in the cylindrical magnet is small and isolated, while the current in the solenoid is along the large circle. In order to prove that the current in the cylindrical magnet is mutually offset, he made a demonstration in public:
Wind the insulated wire into many circles to make a coil. Place a ring made of thin copper sheet inside the coil, take a magnet and place it near the ring. If there is a macro current in the copper ring, the magnetic rod will drive the copper ring to deflect. Otherwise, there is only molecular current. Ampere's experiment shows that there is only molecular current in the copper ring
Later, Ampere repeated the above experiment with a horseshoe shaped strong magnet and found the deflection of the copper ring. However, he tried to explain the macro current induced in the experiment as the result of molecular current. Ampere's idea was still adhered to until his letter to John Herschel (1793-1871) in 1825,In his letter, he said, "These phenomena are caused by the small currents generated by currents or magnets." Although Ampere did not say that these small currents are molecular currents, these currents have the same magnitude order of magnitude as molecular currents. This shows that Ampere's idea of molecular currents is very firm. Unfortunately, he attributed the induced currents to his molecular currents,He doesn't accept induced current alone. He thinks that if he accepts induced current, his molecular current hypothesis will have no place. Otherwise,Electromagnetic induction phenomenonIt is possible to be discovered by Ampere rather than Faraday seven or eight years in advance
In the process of the establishment of Ampere's "molecular current hypothesis", there was also an academic debate between Ampere and Biot. For this debate, physical historians have different views, but one thing is the same, that is, this debate made Ampere more clearly see the necessity of simplifying magnetism into electric current, and also made his "molecular current hypothesis" more clear
Seebeck, a German physicist, also objected to Ampere's molecular current hypothesis. He believed that magnetism is a more essential thing, and current is the result of the action of magnetism
Until later, the view of Ampere was accepted and popularized by F.E. Neumann (1798-1895) and Wilhelm Eduard Weber (1804-1891) in the 1840s, and developed into their electrodynamics
After the "molecular current hypothesis" was put forward, it went through several stages from "unclear", "rejected" to "gradually clear" and became the basis for the development of electrodynamics. This also tells us that scientific discoveries, scientific theories and people's acceptance of scientific achievements will not be smooth, but beneficial academic debates can promote the development of science[3]
