Have high school people ever introduced superconducting materials or superconducting phenomena in ph

High school textbooks do not provide details about superconducting materials or superconducting phenomena. There are only semiconductors and Hall elements, and semiconductors are related to sensors.

There is no magnetic flux in the superconductor, and only the magnetic flux is in the closed coil in the magnetic field.

It is not because there is resistance that there is current, as long as there is voltage, there is a conductor, and there is a current with electrical appliances.

Since there are many coils in the motor, these coils have inductance, the current will not change instantaneously, and the high voltage will be generated to maintain the current, and the air will break down, and there will be a spark, so that the air becomes a conductor to connect the circuit.

It should be a different frequency. If you put it fast, the flat rate is large, the sound is sharper, and if you slow down the frequency, the sound is lower, and the sound is lower. When the recorder battery is not enough and it spins slowly, you can hear a very muffled sound.

Absolute zero. That's 0k minus 273 degrees Celsius. But this temperature is the lowest in the universe.

What cannot be reached artificially can only be approached infinitely.

Some materials at extremely low temperatures.

Superconductivity can occur in some materials at absolute zero.

At ultra-low temperatures, more than minus 200 degrees, some materials can reach superconductors.

Ultra-low temperature, what else ... Forgot.

It's not a matter of accuracy, it's 0

But it is also different from the ideal conductor.

What exactly is a superconducting material?

The properties of superconducting materials and conventional conductive materials are very different. It mainly has the following properties.

Zero resistance: Superconducting materials have zero resistance when they are in a superconducting state, and can transmit electrical energy without loss. If a magnetic field is used to induce an induced current in a superconducting ring, this current can be maintained without attenuation.

This "continuous current" has been observed several times in experiments. Complete diamagnetism: When the superconducting material is in a superconducting state, as long as the applied magnetic field does not exceed a certain value, the magnetic field lines cannot penetrate, and the magnetic field in the superconducting material is always zero.

Josephson effect: When there is a thin insulating layer (about 1nm thick) between two superconducting materials and a low-resistance connection is formed, there will be electron pairs passing through the insulating layer to form a current, and there is no voltage on both sides of the insulating layer, that is, the insulating layer also becomes a superconductor. When the current exceeds a certain value, the voltage U appears on both sides of the insulation layer (a voltage U can also be added), and at the same time, the DC current becomes a high-frequency alternating current and radiates electromagnetic waves outward, and its frequency is where h is Planck's constant and E is the electronic charge.

These properties form the basis for the various applications in which superconducting materials are becoming more and more compelling in the field of science and technology.

Complete diamagnetism refers to the phenomenon that when the metal in the magnetic field is in a superconducting state, the magnetic induction intensity in the body is zero. This phenomenon was discovered by the Dutch scientist Meissner, so it is also known as the Meissner effect. In his experiments, he found that when the spherical tin placed in the magnetic field transitioned to the superconducting state, the magnetic field around the tin ball suddenly changed, and the magnetic field lines seemed to be repelled from the conductor at once.

Further research has shown that the surface of the superconductor can generate a lossless diamagnetic superconducting current, and the magnetic field generated by this current happens to cancel out the magnetic field inside the superconductor.

When the metal is in a superconducting state, the magnetic induction intensity in the superconductor is zero, that is, the magnetic field that originally existed in the body can be squeezed out.

In 1933, Meissner and Ausenfeld in the Netherlands discovered an important property of superconductors: when the metal is in a superconducting state, the magnetic induction intensity in the body is zero, that is, it can squeeze out the magnetic field that originally existed in the body. They measured the magnetic field distribution of the single crystal tin around the spherical conductor and were surprised to find:

As the solder ball transitions to a superconducting state, the magnetic field around the solder ball changes suddenly, and the magnetic field lines seem to be excluded from the superconductor all at once. This phenomenon in which magnetic field lines are automatically expelled from the metal when the metal becomes a superconductor and the magnetic induction intensity in the superconductor is zero, is called the Meissner effect. Later, people also did such an experiment, in a shallow flat tin plate, put a small volume of magnetic permanent magnet, and then reduce the temperature to make the tin superconductivity.

At this time, it can be seen that the small magnet actually leaves the surface of the tin plate, floats up, and after keeping a certain distance from the tin plate, it hangs in the air. This is due to the complete diamagnetism of the superconductor, so that the magnetic field lines of the small magnet cannot penetrate the superconductor, and the magnetic field is distorted, resulting in an upward buoyant force. Further research has shown that:

The reason why the applied magnetic field cannot penetrate the interior of an object in a superconducting state is that a lossless diamagnetic superconducting current is induced on the surface of the superconductor, and the magnetic field generated by this current happens to cancel out the magnetic field inside the superconductor. This discovery was so significant that the Meissner effect was used to determine whether a substance is superconducting.

In 1911, the Dutch scientist Onnes (1853-1926) measured the resistivity of mercury at low temperatures and found that when the temperature dropped to around minus 269 degrees, the resistance of mercury disappeared! The disappearance of resistance is called zero resistance. The so-called "resistance disappears" simply means that the resistance is less than the minimum measurable resistance of the meter.

Some people may wonder: If the sensitivity of the meter is further increased, will the resistance be measured? This problem can be solved with a "persistent current" experiment.

Zero. If there is no resistance in the circuit, there will naturally be no loss of electrical energy. Once the current is excited in the loop, there is no need for any power supply to add energy to the loop, and the current can continue to exist.

Someone once maintained the current in a ring made of superconducting materials for two and a half years without attenuation. From this it can be that the upper limit of the resistivity is 10 23 ohm centimeters, which is less than one part per trillion of the residual resistivity of the purest copper. The zero resistance effect is one of the two fundamental properties of superconducting states.

Another fundamental property of superconducting states is diamagnetism, also known as the Meissner effect. That is, as long as a superconductor is in a superconducting state in a magnetic field, the magnetization intensity generated inside it is completely canceled by the external magnetic field, so that the internal magnetic induction intensity is zero. That is, the magnetic field lines are completely excluded from the superconductor.

Remember to adopt it.

Near absolute 0 degrees is found when the resistance of the metal is almost 0.

It requires a low temperature of more than 100 degrees below 0, and only a few metals can superconduct at this temperature.

The resistance is zero and the current is very large. Maglev trains are made based on this.