1.1 Magnetism comes from electric current, and the source of magnetism is the spin motion of electrons
1.1.1 “Ci Shi calls iron, or cites it”
As early as the 3rd century B.C., there was a description in “Lv’s Spring and Autumn Period Jiqiu Ji” that “Ci Shi Zhao Tie, or citing it”, describes a magnet for iron pieces as merciful and loving as a mother treats her children. Now, in Chinese, ” The “magnetism” in the “magnet”, the “magnetism” in the Japanese “magnet” originated from the original “ci”
In Sima Qian’s “Historical Records”, there is a description of the Yellow Emperor’s use of a compass car in battle. If true, this may be the earliest record of the application of magnets in the world.
Published in 1044 AD by Zeng Gongliang of the Northern Song Dynasty, “Wujing Zongyao” described the process of making guide fish with artificial magnet pieces: cut iron or steel pieces into fish shape, put them in charcoal fire to burn red, and put the tail pointing to the north diagonally. Water will form a compass with remanence, which can be placed in the bowl of water, and guided by the effect of remanence and geomagnetic induction. “Wu Jing Zong Yao” records that the device and the purely mechanical compass car are used for navigation. Shen Kuo of the Song Dynasty wrote “Mengxi Bi Tan” in 1088. He was the first person to accurately describe the geomagnetic declination (ie, the difference between magnetic north and true north) and to use a magnetized embroidery needle to make a compass. In 1119, he published “Pingzhou Ke Tan” and was the first person to specifically mention the use of a compass to navigate the sea. There is a saying that Marco Polo returned to Europe with the compass invented by the Chinese and played a huge role in the European maritime industry.
The compass is shown in Figure 1-1, and the geomagnetic field is shown in Figure 1-2. As one of the four great inventions that the Chinese are proud of, the key is magnetic materials.
1.1.2 Magnetism originates from current
1.1.3 The source of ferromagnetism
1.1.4 Classification of the magnetic properties of substances by their response to magnetic fields
1.1.5 Magnetic classification of materials according to magnetization curve
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