[Benji Butzin]

Benji Butzin  asked the Naked Scientists:
   
Dr. Chris,

Love the information you present and how you do it. My question for you is about magnetic fields. Basically, what elements reflect, refract, or impede a magnetic field? I've done a little research myself but I am unable to find anything that explains the interaction of elements or materials on a magnetic field.

Also, a shot in the dark, are there any experiments dealing with magnetic fields and mercury?

Please break down the information for me in your unique way since it makes sense to me. I'm a non-scientist but seem to understand the information when it is broken down by you.
 
Thank you and keep up the good work.
Benji

What do you think?

[CZARCAR]

lead=Pb?

[Bored chemist]

lead=Pb?

If it's cold enough (below about 7.2 K).
http://en.wikipedia.org/wiki/Meissner_effect

[Phractality]

Superconductors and ferromagnetic materials (not permanent magnets) act like mirrors to magnetic materials. The field generated by currents and atomic spins in a flat surface is like a mirror image of the external field that produces it. This cancels the field that otherwise would be present on the other side of the surface. Outside a closed mirror surface, you see a reflection of the external field; inside the closed surface you see nothing. Consequently, there are no magnetic fields inside a closed ferromagnetic box. So you can protect a magnetic tape by enclosing it in an iron box.

However, there is a limit to how strong a magnetic field can be without penetrating a ferromagnetic shield. Once the materially is magnetically saturated, it becomes transparent to additional fields.

[CZARCAR]

lead=Pb?

If it's cold enough (below about 7.2 K).
http://en.wikipedia.org/wiki/Meissner_effect

me2stupid4that but=magnetic force relies on  &- for opposites whereas emf radiant relies on hot/cold for opposites?

[graham.d]

This is strange because my post replying to this yesterday has disappeared.

For what it's worth, there is a nickel-iron alloy called mu-metal which has a very high permeability so that it greatly attenuates a magnetic field.