Knowledge points: repulsive force of like poles is unable to stably hold the train. But if the superconductor is placed on top of the magnet, stabilize superconductor can be stabilized, because the magnetic field cannot penetrate the superconductor, and the magnetic line of force will hold the superconductor up.
China's first maglev train started to run in Shanghai in January 2003. 10 years past,
a high-end concept of Maglev seems to be out of everybody's eyes now. But this year in China, construction of the second low-speed maglev line, Beijing S1, started, which again brought the cool word “maglev” to the new generation. How does the buoyancy of the maglev train come? Is it the same phenomenon as the repulsion of like poles?
As it is known to all, maglev train is run on top of 1 Telsa permanent magnets which are made from neodymium rare earth magnetic material.
If one magnet is put on top of the other, they would be mutually exclusive as if the magnet would float up. But soon we will find that the magnet on top can’t keep the balance and stability, and it would fall down with just a little sign of trouble. The hidden secret of such phenomenon is Earnshaw's theorem, which put forward by a British Mathematician Earnshaw in 1842.Earnshaw found that stable suspension of an object is impossible to be realized only by permanent magnets or the electromagnetic force between permanent magnets and soft magnets, which is later proved theoretically by him. That is to say, it is impossible to maintain stable suspension of a train by the repulsive force between two magnets, the train will be overturned.
What about that? Magnetic suspension is out of the question?
Fortunately, scientists have found that, if the superconductor is placed on top of the magnet, then stability of the superconductor can be maintained, just as ship will not capsize even encountered wind and the waves. The law of physics of this has gone beyond the previously mentioned Earnshaw theorem; it is Meissner effect: magnetic field cannot penetrate the superconductor, and the magnetic lines of force will prop up the superconductor. This sounds a bit complicated, but, think about the chapter about buoyancy of liquid in junior high school physics class, which mentioned that Archimedes found that the buoyancy of the law in the bath. A hollow ball will float when placed in water, which is very common in lives.
Is it the same logic for Magnetic levitation?
It's similar! Just think of the magnetic field as water. If we put a superconductor in a magnetic field, it would be like hollow iron ball placed in the water. Water can’t find its way into the hollow ball, just as the magnetic field is unable to penetrate the superconductor,
which is the reason why magnetic field creates suspension of superconductor. Meissner effect is a macroscopic phenomenon of quantum mechanics. So, if you want to completely understand the source of the suspension of the maglev train, you should go for the book of quantum mechanics. Eighteenth Century is the age of the steam engine, nineteenth Century is the era of electricity, twentieth Century is the era of IT and the Internet, twenty-first Century is the era of quantum！
