One of the earliest academic discourses was written by the French scholar Pierre de Marek in A.D. 1269.
De Malik carefully marked the orientation of the iron needle at various positions near the block magnet, and drew many magnetic lines from these marks.
He found that these magnetic lines of force meet at both ends of the magnet, just as the meridians of the earth meet at the South Pole and the North Pole.
Therefore, he called these two positions magnetic poles.
Almost three centuries later, william Gilbert thought that the earth itself was a big magnet with two magnetic poles, one at the South Pole and the other at the North Pole.
Gilbert's magnum opus on magnets was published in 1600, which initiated magnetism as an academic field of orthodox science.
1824, Simeon Poisson developed a physical model, which can better describe the magnetic field.
Poisson believes that magnetism is produced by magnetic charges, the same kind of magnetic charges repel each other, and the different kinds of magnetic charges attract each other.
His model is completely similar to the modern electrostatic model; A magnetic charge produces a magnetic field, just as a charge produces an electric field.
This theory can even correctly predict the energy stored in the magnetic field.
Although Poisson model has its success, it also has two serious defects.
First, the magnetic charge does not exist.
Cutting a magnet in half will not produce two separate magnetic poles, and these two separate magnets will have their own guiding poles and north poles.
Secondly, this model can't explain the strange relationship between electric field and magnetic field.
1820, a series of revolutionary discoveries prompted the opening of modern magnetic theory.
First, Danish physicist hans oersted discovered in July that the current of a current-carrying wire would exert a force on the magnetic needle, making it deflect and point.
Later in September, just a week after the news reached the French Academy of Sciences, André-Marie Ampère successfully conducted an experiment, which showed that if the current flows in the same direction, two parallel current-carrying wires will attract each other; Otherwise, if the flows are opposite, they will repel each other.
Then, French physicists Jean-batiste Biot and Felix Savart published Biot-Savart Law in June+10, 5438. This law can correctly calculate the magnetic field around the current-carrying wire.
1825, Ampere published Ampere's Law.
This law can also describe the magnetic field generated by current-carrying wires.
More importantly, this law helps to establish the foundation of the whole electromagnetic theory.
183 1 year, michael faraday confirmed that a time-varying magnetic field would generate an electric field.
The experimental results show a closer relationship between electricity and magnetism.
From 186 1 to 1865, james maxwell synthesized the classical chaotic equations of electricity and magnetism, and successfully developed Maxwell's equations.
First published in his 186 1 paper "On the Line of Physical Force", this set of equations can explain various phenomena of classical electricity and magnetism.
In the paper, he put forward the "molecular eddy current model", and successfully popularized Ampere's law, adding a project about displacement current, called "Maxwell correction project".
Because the molecular vortex packet is elastic, this model can describe the physical behavior of electromagnetic waves.
Therefore, Maxwell deduced the electromagnetic wave equation.
He also calculated the propagation speed of electromagnetic waves and found that this value is very close to the speed of light.
The alert Maxwell immediately concluded that light waves were electromagnetic waves.
Later, in 1887, heinrich rudolf hertz made an experiment to prove this fact.
Maxwell unified the theories of electricity, magnetism and optics.
Although classical electrodynamics is basically completed by Maxwell equations with great functions, theoretically, the 20th century has brought more improvements and expansions.
Albert Einstein showed in his paper 1905 that electric field and magnetic field are the same phenomena observed by observers in different reference systems.
Later, electrodynamics and quantum mechanics merged into quantum electrodynamics.