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               I. MULTI-MAGNETIC LEVITATION OF A MAGNET

Tt The Figure 1. illustrates one of the many types of ways magnetic levitation can take place, we can see small cylindrical magnets floating between a ferromagnetic material and magnets. Such phenomenon is called multi-magnetic levitation. During the experiment the person in the video used two wooden platforms. On the lower platform he put two rectangular objects of ferromagnetic material. On the upper platform, the person put two big cylindrical magnets and stacked them together on top of each other. Then the person put small cylindrical magnets in between and observed them levitating. Levitation is a free-floating of an object in air due to magnetic forces. Figure 1 shows the set-up of the experiment and forces acting on the small magnet.

 

In order to understand why the magnets are levitating, we must dig into the natural phenomenon called magnetism. Magnetism is a phenomenon of the mutual result of electrons’ velocity and spin. Each moving charge produces a portion of magnetic field around itself, resulting in a mutual magnetic field, which we represent by magnetic field lines. Similar to electric field lines, they show the direction and intensity of the field, however, they start from the north (N) pole and come together at the south (S) pole. Every magnet is a dipole which means that it has a north and south pole that can never be separated. The interaction of two magnetic fields results in either attractive or repulsive force. If like poles from two magnets come near each other (i. e. N and N or S and S) they will repel. This happens because the magnetic field lines of opposite directions repel each other and create a repulsion force. On the other hand, when two unlike poles come together (i.e. N and S), they attract. The attraction happens because the directions of magnetic lines match and they generate attractive magnetic force.

Also, a magnetic field can magnetize specific materials called ferromagnetic materials. Ferromagnetism is property of a material which allows material to be magnetized by a magnetic field. The object magnetizes in a direction of a magnetic field. So, for example, if the small magnet from (Figure 1) is facing the ferromagnetic material with the north pole position, it will magnetize so that the direction of the magnetic field inside the object matches the direction of magnetic field of the small magnet.

 

Now, when a small permanent magnet is placed inside the system, its magnetic field comes into contact with the magnetic field of the  magnets located on the top. Because they are facing each other with opposite poles, there is a magnetic force of attraction between them. Also, the specimen magnetizes the material located on the bottom, causing the attraction force. There are two forces that act on a small magnet, both of them are attractive, but it the opposite direction. There is also a gravitational force acting on the specimen magnet. However, the magnitude of the upward attraction force equals the sum of the downward gravitational and attractive forces. The vector sum result of those three is 0, and therefore, the object levitates.

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II.              LEVITATION OF A MAGNET DUE TO SUPERCONDUCTOR

Levitation of a magnet can be also achieved by Meissner Effect. We can observe this effect in Figure 2. The Meissner Effect is the exclusion of magnetic field flux from an object in its superconductive state. A superconductive state is a state of a conductive material at which its resistance is equal to 0 which results in a current flow without any outside electric potential. The superconductive state can be achieved by cooling the object to temperatures close to 0 Kelvin. The current on the surface of the object induces its own magnetic field. During the Meissner effect the magnetic field flux only penetrates through the surface layer of the superconductive material, while the object itself is field-free inside. However, when the magnetic field is too strong, it penetrates the object and therefore breaks the Meissner effect, destroying its superconductive state.  

 

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There are several types of superconductors. Superconductors of Type I have a temperature close to 0 Kelvin and the critical field of 0.2 Tesla, which means that any magnetic field with the strength over 0.2 Tesla will penetrate the superconductor and rid its superconductive state. Type II superconductors are similar to Type I, however they have slightly higher superconductive temperatures and a critical magnetic field of more than 15 Tesla. Usually, to obtain the superconducting state liquid Helium is used, it allows the superconducting material to reach a temperature near 4 Kelvin. However, there is another type of superconducting material which are called high-temperature superconductors. The temperature of the superconductive state is much higher than type I and II. Moreover, it is higher than the temperature of the liquid Nitrogen (77 K), which is used to cool to optimal operating temperatures. The temperatures of superconductive state of these superconductors ranges from 90 to 140 Kelvin. They are usually made of a ceramic material with copper, while type I and II superconductors are mostly pure materials such as Aluminum or Copper. 

In the second figure superconductive material, liquid nitrogen, and a magnet is necessary to achieve this type of magnetic levitation. The superconductor is  cooled using liquid Nitrogen to bring it to its superconductive state. Then placing a magnet on top of the superconductor and releasing it results in levitation of the magnet could be potentially observed. The currents inside superconductor generated their own magnetic field, and  the Meissner Effect occurrs when the magnet is released above the superconductor and its magnetic field lines repelled from magnetic field lines of the superconductor.