Is it possible to understand the past through magnetism?

It should be like tape from a tape recorder.

We already know a lot about electricity, but we don't know much about magnetism, which is related to the lag in the development of magnetic detectors. When it comes to gemstones, half of us believe and half don't, and there is no hard evidence for believing or not believing, the key is that we still don't know much about magnetism. Maybe the progress of magnetism will give us a big step forward in our standard of living!

The magnetism of permanent magnets can be explained by the ampere molecular current hypothesis, each molecule is composed of an atomic nucleus and electrons rotating around it, and the rotating electrons can be regarded as a small annular current (molecular current), and the molecular currents in the permanent magnet are arranged relatively neatly, and the magnetic inductance intensity they produce is in the same direction, showing macroscopic magnetism.

So, why does a moving charge or electric current produce a magnetic field?

If memory serves, Albert Einstein once said that he proposed the special theory of relativity with the original intention of solving the mystery of the relationship between the magnetic and electric forces. According to the special theory of relativity, not only time and length are relative, but force is also relative. That is, observing the same force in different frames of inertia will result in different results.

For example, if there are two moving point charges in space, and the other point charge is observed in the frame of reference of one point charge, the force to which it is subjected satisfies Coulomb's law (Coulomb's law satisfies the charge at rest regardless of whether the charge at rest acts on the moving charge). In the "stationary" frame of reference in which the observer is located, the force on it does not satisfy Coulomb's law, but an extra increment, which is the magnetic force. To put it mildly:

The magnetic field force is a manifestation of the relativistic effect of the electric field force. The above-mentioned charged charge is subject to both the Coulomb force and the magnetic field force in our opinion. The reason why we usually see the magnetic field force between the wires instead of the Coulomb force is because there are both positive and negative charges in the wires.

The general explanation of magnetism is that the electrons around the internal atoms or molecules move in the same direction, so it is similar to the law of electromagnetic induction learned in high school, each atom or molecule is equivalent to a small magnet, so when the ferromagnetic substance receives the influence of the magnetic field in the magnetic field, almost all the electrons of the atom or molecule tend to be the same, so it is magnetized, and it is magnetic.

。Because the principle of magnetism is explained as follows: there are many tiny current rings inside the general object (such as the circular motion of electrons to form a current loop), and these current loops will produce the corresponding magnetic effect, because the direction of the magnetic field generated by the internal current loop of the general object is chaotic, and the magnetic field strength in all directions cancels each other, so the object is macroscopically non-magnetic; From this, it can be thought that the magnetism of magnets is due to the fact that some of the tiny circuits inside the object are arranged in a certain way for some reason (such as placing a non-magnetic iron block in a constant magnetic field for a long time), and the total magnetic field strength in one direction is greater than that in the other directions, so it exhibits magnetism.

Ampere argues that there is a toroidal current in the molecule of any substance, called a molecular current, and that the molecular current is equivalent to a primitive magnet. When the substance is not magnetic on the macroscopic level, the orientation of these molecular currents is irregular, and the magnetic effects they produce on the outside world cancel each other, so that the whole object is not magnetic. Under the action of the external magnetic field, the individual molecular currents equivalent to the primitive magnet will tend to be oriented in the direction of the external magnetic field, making the object appear magnetic.

This is the molecular current hypothesis proposed by Ampere in order to explain the phenomenon of permanent magnets and magnetization.

Usually before the object is not magnetized, the internal human charge is chaotic, and the external behavior is not magnetic. When subjected to strong magnetic magnetization, the direction of the internal charge is unified, that is, a magnetic force is generated.

After magnetization, the internal charge of ordinary iron materials will return to clutter as soon as it leaves the magnetic field. Permanent magnets, on the other hand, do not change their internal charge after magnetization and are permanently magnetic.

In the pre-Qin period, our ancestors had accumulated a lot of knowledge in this area, and when exploring iron ore, they often encountered magnetite, that is, magnets (the main component is ferric tetroxide). These discoveries were documented very early. These discoveries are first documented in several chapters of the Pipe:

There is a magnet on the mountain, and there is gold and brass under it. Other ancient books such as the Classic of Mountains and Seas have similar records. The iron-absorbing properties of magnets have been discovered very early, and the nine volumes of "Lü's Spring and Autumn" have mastery chapters

Ci Zhao Tie, or lead to it. At that time, people called "magnetism" "compassion", and they saw the magnet's attraction to iron as a mother's attraction to her children. And think:

The stone is the mother of iron, but there are two kinds of stones: benevolent and unkind, the loving stone can attract his children, and the unkind stone cannot attract him. Before the Han Dynasty, people wrote the magnet as "Cishi", which means loving stone. Since magnets attract iron, can they also attract other metals?

Our ancestors made many attempts and found that magnets could not attract not only metals such as gold, silver, and copper, but also bricks and tiles. In the Western Han Dynasty, people have realized that magnets can only attract iron, but not other items. When two magnets are placed close to each other, sometimes they attract each other and sometimes repel each other.

Now people know that magnets have two poles, one called the n pole and the other called the s pole. Opposite-sex poles are mutually exclusive, and opposite-sex poles attract each other. At that time, people didn't know about this truth, but they were still aware of it.

In the Western Han Dynasty, there was a monk named Luan Da, who used this property of the magnet to make two chess pieces, by adjusting the mutual position of the polarity of the two chess pieces, sometimes the two chess pieces attracted each other, sometimes they repel each other. Luan Da called it "fighting chess". He dedicated this novelty to Emperor Wu of Han and demonstrated it on the spot.

Emperor Wu of the Han Dynasty was amazed, and the dragon's heart was so happy that he actually named Luan Da as the "General of Wuli". Luan Da used the nature of the magnet to make a novel gadget to deceive Emperor Wu of the Han Dynasty. The Earth is also a large magnet, and its two poles are close to the geographic south pole and the geographic north pole respectively.

Therefore, when the magnets on the earth's surface can rotate freely, they will be repelled by the same sex of the magnets, and the opposite sex attracts the opposite sex. The ancients didn't understand this truth, but they knew this kind of phenomenon very well.