Meisner Effect

Location:

Concepts Shown:

superconduction

Equipment:

Yba2Cu3O7 superconductive disk, small cube magnet, pair plastic tweezers, glass petri dish, liquid nitrogen, gloves & goggles. Cost: $20-$50 This can be purchased as a kit from: Edmund Scientific: (609) 573-6270

Procedure:

Setup: The only setup required is obtaining the materials and perhaps sketching up some diagrams to show simplistically what's going on.

Presentation:

  1. Safety first! (gloves and goggles)
  2. Place superconductive disk in petri dish
  3. Set magnet on disk
  4. Pour liquid nitrogen into petri dish. (enough to completely cover the disk.)
  5. Allow all material to boil until cool
  6. At this point, the magnet should rise up and float in the air above the disk. If it does not, or falls off to the side, use the plastic tweezers to put the magnet back in place above the disk.
  7. Once in place, show that the magnet is truly suspended by spinning it in the air with the tweezers.
Science:

When a magnet moves it causes currents to be induced in whatever conducting materials are within range of its magnetic or "B"-fields. This is also true when the magnet approaches the superconductor. However inside a superconductor, there is no resistance, and this will cause these currents to almost instantly rise to a level which exactly cancels the effects of the B-field it is in, so there is no net field in the superconductor. These supercurrents inside the superconductor make it appear to the permanent magnet as if it were another permanent magnet of equal magnitude but of opposite direction, this is called perfect diamagnetism. At some point these repulsion forces will be enough to overcome the downward pull of gravity on the magnet and the magnet will be suspended above the superconductor. The key to a material being a superconductor is its critical temperature abbreviated Tc. This is the temperature below which the electrons within the material change their most basic quantum feature, spin and can travel uninhibited through the atomic lattice. However, some lattices are better than others depending on their structures. To date, one of the best known structure is what is called Yba2Cu3O7 or 1-2-3. 1-2-3 has a Tc at approximately 93 K - still very cold, but within the working range of liquid nitrogen, 77 K. To date, the highest Tc is at about 125 K in a material containing the elements Tl-Ca-Ba-Cu-O. The future of superconductors looks promising with applications in everything from magnetic levitation trains to super efficient motors to high speed logic circuitry.

References:

Author:
Tyler van Houwelingen
Credits:


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