The hidden armor carries a sword, and it is stopped when entering the door to show the spirit. It is also called Que Humen.

"Book of Jin? Biography of Ma Long": Sometimes the road is lined with magnets, and the thieves are burdened with iron armor, unable to move forward. Long's soldiers are all covered with rhinoceros armor, leaving nothing in their way, and the thieves think they are gods.

This kind of legend is pure nonsense and has no feasibility at all. Not to mention that most of the swords during the Qin Shihuang period were made of bronze. Even if they were made of iron, it was impossible to carry a sword on your back and be attracted by the magnet door.

The same is true for Malone's Magnet Array.

However, these two stories are clearly written in history books. In order to explain this truth, we have the content of this section. If the ancients really wanted to use magnetic fields to prevent people carrying metal weapons from passing, they could only rely on

The principle of electromagnetic induction based on Lenz's law.

This is the time to test the concepts of high school physics. The author learned Lenz’s law about thirty years ago. So I don’t quite understand what the current teachers teach in class. But I don’t know how to teach high school physics.

The working dog is not a good internet writer, so I have the obligation to say a few more words here.

What is Lenz's law? As explained in this section, it is a type of law of inertia. What is the law of inertia? In terms of the most basic mechanics, Newton's first law is the law of inertia. It can be summarized in eight characters - what moves is always in motion, what is static is

is constant. Then Lenz's law is the same. We know that metal (conductor) cutting magnetic lines of force will produce induced current. Induced current will also produce magnetic field. This magnetic field always hinders the change of magnetic flux, or in other words, always blocks the cutting of magnetic lines of force.

this action.

The generation of this induced current is born to counteract the electromagnetic changes produced in the magnetic field. Then the next step is very simple. The conductor will receive force during electromagnetic induction. How to determine the direction of the force? It must be opposite to the direction of the magnetic line of force cut by the conductor.

, which binds the new electromagnetic changes in the magnetic field. Using inertia to understand Lenz's law is much easier to use than the right-hand principle to judge the direction of force in many cases.

Okay, let’s go far. Now let’s return to the content of this article. Suppose that King Shou of Yin, also known as King Zhou, made a door with magnets. There is a magnetic field in the door. How can it be used to hinder people carrying metal sharp objects?

The entry of the person?

The answer is to lay a conductive floor. In this article, a copper floor is used. In this case, the human body acts as a conductor and will cause a potential difference due to electromagnetic induction when stepping. The body and the metal carried will conduct electricity and thus receive a backward pulling force.

The faster it enters, the greater the pulling force it receives. Although the description in this article is still a bit exaggerated, this force is definitely more powerful and effective than the magnetic force itself.

There is a toy in the world that is made based on the principle of Lenz's law. The components are very simple, just a magnet and a metal tube. Put the magnet into the metal tube, and the falling speed of the magnet will be greatly reduced. In this process, the metal tube

They are all connected and form a loop of their own, so the effect of Lenz's law is more intuitive. In this work, this principle is simulated using a cannon post and a magnet.

A cannon is a hollow copper pillar, which is also recorded very clearly in historical records. A fire is burned in the middle for execution. In turn, it can also be used as a channel for a magnetic lifting device.

At this time, if someone insists on asking the author what evidence shows that the ancients knew the principle of Lenz's law. Then I can only talk to you again about Qin Shihuang's Palace Gate and Ma Long's Ci Stone Array.

Hundreds of soldiers?

Regarding the application of Lenz's law, we haven't used it to the end yet. We can see that there are almost no scientific principles that are used only once in this work. The simple tools are all used to spell out something more complex and awesome later.

The device is used as a foundation.

So will there definitely be more complex and awesome electromagnetic devices in the following chapters?
Chapter completed!