What is the Meissner effect?

Question

No answers from the wiki. i don't really understand what it means. so the answer has got to be layman.

i understand that a superconductor has no resistance in it. it is a metal supercooled by liquid nitrogen and stuff. i just don't understand why the Meissner effect can make a magnet float.

Answer 1

It's the repulsion caused by a superconductor's ability to exclude an externally applied magnetic field from its interior. Superconducting currents induced on the surface due to the time variation of the magnetic field as the external magnet approaches the surface create an internal magnetic field contribution that exactly cancels the externally applied field. The currents also cross the surface magnetic field, causing a repulsive Lorentz force.

Re followup. OK, simple. There are basic concepts of electromagnetism (Maxwell's Equation) that you would need to understand to appreciate any answer:
1 A time varying magnetic field (such as a permanent magnet in motion) produces an electric field that will drive current in a conductor orthognal to the field.
2. the current in a superconductor, once induced, persists without resistive lose.
3. Current which cross (are orthogonal to) a magnetic field create a force orthogonal to both.
4. Since there is no resistance to current flow, any electric field within a superconduction it is shorted out quickly.
5. Without a time varying electric field, a given volume cannot change its internal magnetic field.

Answer 2

the expulsion of a magnetic field from the interior of a material that is in the process of becoming a superconductor, that is, losing its resistance to the flow of electrical currents when cooled below a certain temperature, called the transition temperature, usually close to absolute zero. The Meissner effect, a property of all superconductors, was discovered by the German physicists W. Meissner and R. Ochsenfeld in 1933. As a superconductor in a magnetic field is cooled to the temperature at which it abruptly loses electrical resistance, all or part of the magnetic field within the material is expelled. Relatively weak magnetic fields are entirely repulsed from the interior of all superconductors except for a surface layer about one-millionth of an inch thick. The external magnetic field may be made so strong, however, that it prevents a transition to the superconducting state, and the Meissner effect does not occur. Generally, ranges of intermediate magnetic-field strengths, which are present during cooling, produce a partial Meissner effect as the original field is reduced within the material but not wholly expelled. Some superconductors, called type I (tin and mercury, for example), can be made to exhibit a complete Meissner effect by eliminating various chemical impurities and physical imperfections and by choosing proper geometrical shape and size. Other superconductors, called type II (vanadium and niobium, for example), exhibit only a partial Meissner effect at intermediate magnetic-field strengths no matter what their geometrical shape or size. Type II superconductors show decreasing expulsion of the magnetic field as its strength increases until they abruptly cease being superconductors in relatively strong magnetic fields.

Answer 3

The Meissner Effect works just like a smaller magnet levitating over a larger magnet if the like poles are together. I'm not sure how the magnet is stabilized. The magnetic fields from the superconductor encloses around the magnet and thus causes it to levitate.

Answer 4

wiki, help!

http://en.wikipedia.org/wiki/Meissner_effect