# I'm trying to explain some physics principles to a general audience

• sci-guy

#### sci-guy

I'm trying to explain some physics principles to a general audience and have a few related questions:

1) What's the name of the principle that distinguishes between randomly arranged particles in an iron bar and those arranged so as to magnetize it? Is it 'coherence' or something else?

2) Is it the same principle (in a general sense, e.g. 'coherence') that produces phenomena like laser light, superconductivity, superfluidity, etc.? If not (or even if it is), are there other common examples of the same phenomena?

3) Is it correct to say that the particles/waves in these coherent systems "take on field properties"? If not, what's a better way to describe the macroscopic effects.

I'm not looking for long technical answers; brief general explanations will do (hopefully, that's possible for such phenomena).

Thanks.

(1) A simple explanation is that the more completely the electron dipole moments are aligned in a material the more "magnetic" we consider a material. You could characteriize an electron dipole moment as the rough equivalent of the north and south pole of the Earth with it's external magnetic field: an electron also has north and south poles as a result of its "spin"...rotation. The electron cloud is the analogy of the earth...

see http://en.wikipedia.org/wiki/Magnetic_material#Microscopic_origin_of_magnetism

and lots of related discussions via links. But be sure to make the point that ALL materials are magnetic to some degree since all contain electrons. Electrons are loosely bound in atoms unlike neutrons and protons in the nucleus.

(2)
superconductivity is a quantum mechanical phenomenon. It is also characterized by a phenomenon called the Meissner effect, the ejection of any sufficiently weak magnetic field from the interior of the superconductor as it transitions into the superconducting state.

superconductivity and superfluidity are closely related:
http://en.wikipedia.org/wiki/Superconductivity#Theories_of_superconductivity

Sounds like you are aware of the BCS theory of superconductivity:
http://en.wikipedia.org/wiki/Superconductivity#Theories_of_superconductivity

When I briefy studied BCS, hightemp superconducivity wasn't even known...
More here, I'll leave it to others to tackle as I'm unsure just how well we we really understand superconductivity.
http://en.wikipedia.org/wiki/Ginzburg-Landau_theory

Thanks -- guess I was looking for a single, simple term like "in phase" or exhibiting "coherence," but maybe there isn't one. Seems like all these phenomena (magnetism, laser light, superconductivity, etc.) share a common feature of aligned structure. Thought there was a single priniciple to explain it.