Electromagnetism is part of classical physics, and when it comes to electromagnetism, it is necessary to mention Maxwell, the founder of classical electrodynamics.
Maxwell's fame does not seem to be as well-known as Newton and Einstein, after all, when Newton is mentioned, this formula seems to emerge as if it were a conditioned reflex (not to mention force analysis); when Einstein is mentioned, the theory of relativity is already known to women and children. But when we mention Maxwell, it's the head-on challenge
Maybe that's why Maxwell wasn't as famous as Newton. After all, if you take one of the four equations in Maxwell's equation system, you can introduce one or two periods.
A unified journey through electromagnetism
As early as the Spring and Autumn Period and the Warring States Period, there was a record that "there are people with benevolent stones on the mountain, and there are copper and gold under them". It can be seen that people's understanding of magnetic phenomena can be traced back to a long time ago. The phenomenon of static electricity was only recorded in the Western Han Dynasty.
In 1600, Gilbert, the imperial physician of Queen Elizabeth of England, published "On Magnets", which made important contributions to the study of natural magnets and geomagnetism. At the same time, he also found that many substances, such as diamond, sapphire, resin, alum, etc., can attract tiny objects after friction, but these properties are not like magnetic phenomena can guide the north, so he called this property "electric" and invented the first electrometer.
In order to preserve the electricity in the air, in 1745, Mushinbrock of Leiden, the Netherlands, invented the original form of the capacitor - the Leiden bottle. The invention of the Leiden bottle provided favorable conditions for the further study of electricity. At about the same time, Franklin proposed that electricity is an element that exists in all matter and can be transferred by friction. He believes that objects that get electricity from friction are positively charged, and objects that lose electricity are negatively charged. The term positive and negative electricity is still used today.
In the late 18th century, scientists began to study the interaction of charges. In 1766 , Priestley speculated that the interaction between electricity and gravity should be similar to gravity , i.e. that the magnitude of the force was inversely proportional to the square of the distance , but no proof was given.
In 1773, Cavendish gave the result that the inverse relationship between electricity and distance squared was no more than 2%, confirming Priestley's suspicions. In 1785, Coulomb designed the torsional scale experiment, which directly determined the inverse square and product proportional relationship of the interaction of two stationary charges.
Although Franklin observed as early as 1750 that Leyton's bottle discharge could magnetize steel needles, and even earlier it was discovered that lightning affected compasses, by the 19th century the scientific community also believed that electricity and magnetism were two different things.
However, the Danish natural philosopher Oster took the opposite view, and under the influence of Kant, he firmly believed that there was a relationship between electricity and magnetism. Eventually he discovered that the passage of current through the wire would cause the magnetic needle to deflect, and he discovered the magnetic effect of the current.
Auster's current-magnetic effect opens a new door to electromagnetic research. At about the same time afterwards, Ampere discovered the magnetic effect of the current-carrying coil (that is, the middle school teacher often asked you: do you dare to reach out and draw a comparison to let you know what is called the right hand (the rule)), Arago studied the magnetization of steel and iron under electric current, and Biot and Safar studied the effect of wires on the magnetic polar force. These results further bring the relationship between electricity and magnetism closer.
The magnetic effect of electric current was eventually applied to make electricity for people's production and life, especially during the Second Industrial Revolution, the use of electricity greatly improved people's productivity, but also promoted the development of electromagnetic research.
In 1833 Gauss and Weber made the first single-wire telegraph, and in 1837 Wheatstone and Morse independently invented the telegraph machine, which could transmit information on paper tape through Morse's code. In 1876, Bell invented the telephone, which allowed the electromagnetic effect to transmit people's voice information.
In addition to applications, the invention of the current detector using the magnetic effect of electric current has also greatly promoted the development of related disciplines. Because of the advent of ammeters, Ohm provided the conditions for discovering the law of current. But because the concept of conservation of energy has not been formed, people are still confused about the thermal effect of electric current. It was not until 1848 that Kirchhoff examined the circuit from the perspective of energy and figured out the concepts of potential difference, electromotive force, and electric field.
Since we know that electric current has a magnetic effect, then magnetism must also have an electrical effect. The famous physicist Faraday studied the phenomenon of electromagnetic induction and determined the law of electromagnetic induction, that is, the law of induced electromotive force depending on the change of magnetic field with time.
But Faraday's mathematics is not good, the real expression is given by Neumann, and the direction of the induced current is given by Lengzi. On this basis, Faraday built the first generators and electric motors. In addition, he also suggested that the distribution of electromagnetic fields in space should be described by "power lines" and "magnetic field lines", and pointed out that these lines are all material, and electricity and magnetic forces are transmitted by these lines, and the "source" is studied according to the "generation" and "convergence" of the lines.
The veil of electromagnetism has been gradually lifted, but an integration is needed. That's when our protagonist Maxwell comes on the scene. Not so early physicists such as Neumann and Weber also wanted to unify electromagnetic phenomena, but their view of distance action made them unsuccessful.
Faraday's idea of "lines" inspired Maxwell. He tried to unify electromagnetism by analogy with electromagnetic phenomena and mechanical phenomena. He believes that a changing magnetic field would excite a vortex electric field. Conversely, the changing electric field also generates a magnetic field, which introduces the concept of "displacement current". In this way, the electrical displacement will excite the magnetic field.
Thus, combined with the results of previous generations (Gauss's theorem, ampere's loop theorem, and Bio-Safar's law, etc.), Maxwell summed up the ultimate formula for electromagnetism, Maxwell's system of equations:
If we simply understand these formulas, we may wish to regard it only as describing the direction of space, and as to how it changes, we will not consider it, then the first formula shows that if in a given closed surface, the electric field strength flux through the surface depends on the charge in the closed plane; the second formula is to replace the electric field of the first formula with a magnetic field, if you take a closed loop, the current intensity through the loop is related to the magnetic induction intensity; the third formula shows that the changing magnetic field will produce an electric field The fourth formula states that the magnetic field is generated by a changing electric field and a displacement current. Using Maxwell's equations, we can also calculate the speed of light.
In this way, light and electromagnetic waves are also linked, that is, Maxwell unified light, electricity, and magnetism.
Heaven forbid
The ancients said: The heavens will send great things down to the Si people, and they will first suffer their hearts, strain their bones, and starve their bodies.
But for Maxwell, this phrase does not seem to apply. Maxwell's life can be said to be very ordinary, not as low-key as The Lark of Gold, nor as charming as the playboy Schrödinger. Arguably one of the few "normal" scientists.
But gold always shines, and at the age of 16, he was admitted to the University of Edinburgh and began to live a life of open hanging (and also has a scientist-specific hairline). In 1850 he transferred to the University of Cambridge to study, and after graduation he stayed on to work. Maxwell began his work on electromagnetism from 1954 until 1873, when his magnum opus, On Electricity and Magnetism, was published. Just six years after publication, in 1879, Maxwell died.
Maxwell did not enjoy the honor he deserved during his lifetime, because the importance of his scientific ideas and scientific methods was not fully realized until the advent of the scientific revolution in the 20th century.
If we look back at the dates of Maxwell's birth and death, we find two amazing coincidences—the year Maxwell was born, Faraday discovered electromagnetic induction; the year Maxwell died, Einstein was born.
epilogue
Any discipline has its own unique history of development, which is the product of long-term human activities and theoretical thinking. In the process of reviewing the history of the development of the discipline and the scientists who have made important contributions to the development of the discipline, in addition to understanding the way of thinking and thinking methods of the scientists themselves, it is more important to understand how people have built a solemn scientific edifice on the barren wilderness.
In fact, for physics exams, it's best to pay homage to Maxwell, because his name is James Clerk Maxwell, Max well, which is extremely good. Here to borrow the name of this physics giant, I wish you all the best luck in the new year (in fact, I would prefer peach blossom luck), Max Well.
About the author: Liang Tianyu, who did not want to be named, is currently a master's student in particle physics and nuclear physics at Central China Normal University, and his research direction is to find neutrino-free double beta decay. Academics are not refined, the art is not successful, what to do, do their best to do some related science popularization work to show their use, deficiencies are still expected to be corrected.