19 1 1 year, Dutch scientist Anis found that when the temperature dropped to MINUS 269 degrees, the resistance of mercury actually disappeared! The disappearance of resistance is called zero resistance. The so-called "resistance disappearance" only means that the resistance is less than the minimum measurable resistance of the instrument. Some people may think: if the sensitivity of the instrument is further improved, will the resistance be measured? This problem can be solved by "continuous current" experiment. Zero. If the loop has no resistance, there will naturally be no loss of electric energy. Once the current is excited in the loop, it can continue to exist without any power supply to replenish energy to the loop. Someone once put the current in a ring made of superconducting material for two and a half years without attenuation. Therefore, the upper limit of resistivity is 10-23 ohm cm, which is less than one billionth of the residual resistivity of the purest copper. Zero resistance effect is one of the two basic properties of superconducting state.
The loop composed of normal conductors has resistance, which means the loss of electric energy, that is, the conversion of electric energy into heat. In this way, if there is no power supply to continuously replenish energy to the loop, all the electric energy in the loop will be consumed in a very short time (for example, microseconds), and the current attenuation will be zero. If the loop has no resistance, there will naturally be no loss of electric energy. Once the current is excited in the loop, it can continue to exist without any power supply to replenish energy to the loop. Someone once put the current in a ring made of superconducting material for two and a half years without attenuation. Therefore, the upper limit of resistivity is 10-23 ohm cm, which is less than one billionth of the residual resistivity of the purest copper. Zero resistance effect is one of the two basic properties of superconducting state.
Another basic property of superconducting state is diamagnetism, also known as Messner effect. That is, as long as the superconductor is in a superconducting state in the magnetic field, the magnetization generated inside it completely cancels out with the external magnetic field, so that the internal magnetic induction intensity is zero. In other words, the magnetic field lines are completely excluded from superconductors.
Conductors in superconducting state are called superconductors. The DC resistivity of superconductors suddenly disappears at a certain low temperature, which is called zero resistance effect. Without the resistance of the conductor, the current will not cause heat loss when it flows through the superconductor, and the current can form a strong current in the conductor without resistance, thus generating a super-strong magnetic field.
1933, meissner and Olsenfeld of the Netherlands discovered another extremely important property of superconductors-when the metal is in a superconducting state, the magnetic induction intensity in the superconducting body is zero, but the original magnetic field in the body is squeezed out.
The experiment of single crystal tin ball shows that when the tin ball transits to superconducting state, the magnetic field around the tin ball suddenly changes, and the magnetic field lines seem to be suddenly excluded from the superconductor. People call this phenomenon "Mesner effect", which was discovered by Walter Mesner and Robert Oxenfield when they measured the magnetic field outside superconducting tin and lead samples in 1933.
In the presence of a magnetic field, the samples are cooled below their superconducting phase transition temperature. Below the phase transition temperature, the sample almost cancels all the internal magnetic fields.
They only discovered this influence indirectly; Because of the conservation of magnetic flux of superconductors, when the internal magnetic field weakens, the external magnetic field increases. This experiment proves for the first time that superconductors are not only ideal conductors, but also provide a unique definition property for superconducting states.
Can you refer to more information? Superconducting phenomenon