“Who can explain this”

2 comments ↓

#1 Whitaker on 01.13.09 at 6:28 pm

Cold can have an effect on magnetism, because cold can have an effect of how fast charged particles move. It is the motion of charged particles, usually electrons around a nucleus, that produces magnetic fields. Cooling a metal can make the motion within less random, thus allowing more atoms to line up
with each other. This increases the magnetic field of the material. On the other hand, making a magnet very hot will cause more random motion, resulting in less allignment of molecules and less megnetism.

Diamagnetic objects have other properties, don’t get me started…

Hope this helps !

#2 Whitaker on 01.13.09 at 6:33 pm

In a weak applied field, a superconductor expels all magnetic flux. Although the magnetic field is completely expelled from the interior of the superconductor, there is not a sharp transition at the edges of a sample, but rather a rapid decay of field into the sample over a distance, the penetration depth. Each superconducting material has its own characteristic penetration depth.

When the temperature of a superconductor in a weak magnetic field is cooled below the transition temperature, surface currents arise that generate a magnetic field which yields zero net magnetic field within the superconductor. These currents do not decay in time, thus establishing that perfect diamagnetism implies zero electrical resistance. Called persistent currents, they only flow within a depth equal to the penetration depth, whose theory was given in the London equations by the brothers Fritz and Heinz London.

This was Quoted from http://en.wikipedia.org/wiki/Meissner_effect

They say it so much better than me !!