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This prediction may be correct. But Feynman also knew that Maxwell didn't discover all the laws of electrodynamics at once, so if he had to choose a representative time, he would probably choose1864101October 27th. Maxwell explained his paper "Dynamic Theory of Electromagnetic Field" to the members of the Royal Society that day. A year later, Maxwell officially published his radical new theory. At that time, the whole theory was still very lengthy, and later his followers refined it into four famous equations. In any case, it is meaningful to call these equations Maxwell equations. So we are going to celebrate their150th birthday today.
Before 1820, scientists thought that electricity and magnetism were two completely different phenomena. Later, hans christian oersted reported an amazing result: when he put the magnetized compass near the live wire, the compass moved to an angle perpendicular to the wire. Scientists everywhere were shocked and immediately began to study the relationship between electricity and magnetism. One of them is michael faraday.
James clerk maxwell is the most influential figure in physics in19th century.
Faraday, the son of a blacksmith in London, taught himself. At the age of 29, he worked for humphry davy, the Royal Institute. As an analytical chemist, he is famous for his wit, sensitivity and reliability. Only when everything else was done did he begin to do experiments in electricity and magnetism. He doesn't know mathematics, so at least on the surface, he is lacking compared with those well-educated contemporaries. But on the other hand, this lack has become his advantage, and he can think more freely than others. He asked many questions that others had not considered, designed experiments that others had not thought of, and saw opportunities that others had missed.
His contemporaries, Andre Marie Impert, repeated Oster's experiment at an alarming rate. A whole set of mathematical theories was developed in a few months. He said that any current loop will produce a magnetic force running through it. Ampere's theory, like Coulomb before, is based on Newton's theory of universal gravitation. Coulomb thinks that linear electric power and magnetic force will be generated immediately between point charge and magnetic pole. These forces are inversely proportional to the square of the distance. Ampere calculates the magnetic force generated by electrified wires by treating them as infinite current segments in series and each infinite current segment as a point. To calculate the magnetic force produced by electrified wires, it is only necessary to add up the effects of all current segments by mathematical methods.
In Faraday's view, it is wrong to say that the compass in Oster's experiment is driven by a set of linear gravity and the repulsion between it and the wire. He felt that the electrified wire should have caused a circular force in the surrounding space. He tested the idea with a clever and simple experiment. Faraday fixed a magnet vertically in the center of a small washbasin, and poured mercury into the washbasin until only the top of the magnet was exposed. Then he put a wire into mercury. When he is electrified, wires and mercury are part of the circuit. The top of the metal wire in contact with mercury rotates rapidly around the magnet. He made the first electric motor in the world.
Ampere has proved how to generate magnetism from electricity, so it is certainly possible to generate electricity from magnetism. However, scientists have tried for ten years and failed. Then at 183 1, Faraday found the reason why this goal could not be achieved: in order to generate current in the conductor, you must change the magnetic field state of the space around the conductor. All you have to do is move a magnet around the circuit (and vice versa), and the circuit will have current. But what exactly is the magnetic field state of space? Faraday remembers the distribution of iron filings around magnets on white paper. He is convinced that the magnet is not only a piece of iron with interesting characteristics, but also the center of the spatial distribution of the whole magnetic force curve, and the magnetic field lines actually exist. Moreover, this phenomenon is not just ferromagnetic: there are similar magnetic lines around the conductive circuit.
Faraday came to a further conclusion. Through the test, he came to the conclusion that every charged object is the source of power lines and will bend in space. Unlike continuous circular magnetic field lines (they don't end in a magnet, but pass through it), magnetic field lines always go from a positively charged object in one place to a negatively charged object in another. So every positive charge has a balance with negative charges elsewhere. At the same time, he observed that neither magnetic effect nor electric effect is instantaneous, and it takes some time for them to have an effect. According to his understanding, this is the time needed for the system to establish these electric power and magnetic lines.
British scientist Mike Faraday (portrait) helps Maxwell develop the unified theory of electromagnetism.
Faraday and other scientists have very different ways of thinking. Generally speaking, scientists still believe that electricity and magnetism interact with physical objects within a certain distance, while the role of space is negative. Sir george biddell airy, a royal astronomer, commented that Faraday's magnetic field lines were "fuzzy and changeable", and he represented the opinions of many people at that time. That's understandable. Their usual teleaction theory has a clear formula, but Faraday's theory does not provide any formula. Although they respect Faraday and think that he is an extraordinary experimenter, most scientists think that he doesn't know mathematics, so he lacks theoretical basis.
Faraday understood their opinions, so he was very cautious when he published the theory of magnetic field lines. He has only had one adventure. It was in 1846, and one of his colleagues, Charles Wheatstone, wanted to give a speech on his invention at the Royal Academy, but he chickened out. So Faraday decided to give a speech himself. Before the end of the specified time, he began to speak outside the notice. He let his guard down and spoke his most intimate thoughts. He told the audience the electromagnetic theory of light with amazing foresight. He speculated that all spaces were filled with electric and magnetic lines. The transverse vibration of these lines, when disturbed, will send out energy waves at a fast but limited speed along the direction of the lines. He said that light is probably a reflection of light vibration.
Now we know that he is very close to the truth. But for Faraday's colleagues, the vibration of light is as absurd as an illusory legend. So that Faraday's supporters were embarrassed, Faraday himself regretted relaxing his ideological defense. He left his contemporaries far behind, and it was forty years before anyone revealed Faraday's true greatness. This person's thoughts are highly consistent and complementary to Faraday's ability. This man is james clerk maxwell.
Maxwell's career was amazing and short (he died at the age of 48). He made great discoveries in every branch of physics he was engaged in. But his greatest work is about electric and magnetic fields, just like Faraday. Maxwell was born into a noble Scottish family. He went to the best middle school in Edinburgh, and then went to Edinburgh University and Cambridge University. Won the second place in the honorary degree examination of mathematics in Cambridge University and obtained a bachelor's degree. After that, he began to read Faraday's electrical experiments. Maxwell was suddenly attracted by Faraday's frankness: the great man publicized his successes and failures and expressed his mature and rough ideas. Reading on, Maxwell saw the real power of this work: before seeking understanding, he made a huge leap in his mind. In Maxwell's view, the concept of line is meaningful in space. Although Faraday is expressed in words, it can be expressed in mathematics in essence. He began to use the power of mathematics to spread Faraday's thoughts. In nine years, he crossed three amazing stages and succeeded.
Maxwell is very good at discovering similarities in different fields of nature. 1856, he began to compare power lines and magnetic lines with a virtual incompressible uniform fluid: the speed and direction of fluid in the spatial region represent the density and direction of magnetic lines. In this way, he proved that static electricity and magnetic force can be deduced from the traditional theory of distance interaction. This is a remarkable achievement. But Maxwell didn't know how to deal with the ever-changing force line at that time. In his usual way, he went to do other jobs, but these ideas were brewing in his mind.
Six years later, he had a new model. He imagined that the space was full of small balls that could rotate and be separated by smaller particles. Those small particles are like steel ball bearings. Maxwell thinks that these balls are small, but they have limited mass and some elasticity. In this way, power lines and magnetic lines can be compared with mechanical systems. So the change of any one ball will cause the change of other balls. This outstanding model deduces all the famous electromagnetic equations, and predicts that the propagation speed of electromagnetic waves is only determined by the basic properties of electromagnetism. This speed is only 1.5% different from the experimental light speed. This is an amazing result, but scientists have not commented on it. They believe that any sub-field of physics is to know the true laws of nature. They think Maxwell's model is not original, and try to explain that electromagnetism and light are flawed with this model. Everyone expects Maxwell's next step is to perfect this model. But he didn't. He put the model aside and built the theory from scratch using only the dynamics principle.
Two years later, the research results were published in the paper "Electromagnetic Field Dynamics Theory". In this model, the ubiquitous medium replaces the rotating particles in the previous model. The medium has inertia and elasticity, but he didn't elaborate on its mechanical properties. Just like juggling, he used Joseph-Louis Lagrange's method and regarded the power system as a "black box": as long as some common features of this system are described, the output can be deduced from the input without knowing the specific mechanism. In this way, he has the electromagnetic field equation, a total of 20 equations. 1864 10, he told his paper at the royal society, and the audience didn't know what to do with it at all. It is bad enough that a theory is based on a strange model, and a theory that is not based on any model is simply incomprehensible.
Until Maxwell died in 1879, several years later, no one could really understand his theory, just like it was displayed in a glass box, which was widely admired but no one could get close to it. Later, oliver heaviside, a self-taught telegraph operator, made this theory approachable. In 1885, he summarized this theory into four Maxwell equations that we now know:
Here e and h are vectors of electric field force and magnetic field force at any point in space, ε and μ are basic constants of electricity and magnetism, ρ is charge density, and j is current density vector. The first two equations concisely express the inverse square law of electricity and magnetism. The third and fourth equations define the relationship between electricity and magnetism, indicating that electromagnetic waves exist and propagate at the speed of1√ (μ ε).
Heweser greatly simplified the expression of the equation by vector analysis. The three-dimensional vector is represented by a letter, which pushes the potential and the magnetic vector potential behind the scenes. 1888, heinrich hertz discovered electromagnetic waves, which greatly promoted people's interest in electromagnetic theory. People turned to the refined version of Havisham instead of Maxwell's original expression.
In order to tell the story completely, we need to add three points. First of all, Maxwell can actually simplify and compress the theory easily, but he thinks it is best to keep some openness. Many years later, his wisdom appeared: richard feynman and others developed quantum electrodynamics, that is, they used the original potential energy rejected by Harvey. The second point is that Maxwell named operational symbols, such as divergence and curl. Thirdly, Maxwell actually used vectors in his papers on electricity and magnetism, but he took the expression of vectors as an extra choice. His vector is derived from William Ron Hamilton's complex quaternion. Most people don't want to use such a complex vector system, and they didn't begin to accept it until Hevesey introduced a much simpler system.
Finally, consider this point: although Maxwell never deliberately pursued it, his equations revealed that the speed of light is 1/√(με), which has nothing to do with the relative speed of the observer and the light source. This leads to Einstein's special theory of relativity, E = mc. Therefore, perhaps the most famous formula in the world should be E = m/με. Only in this way can we reflect the joint contribution of Einstein and Maxwell.
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Source | Microwave Radio Frequency Network
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