Dirk Bruere at Neopax wrote in message ...
Bernhard Kuemel wrote:

Dirk Bruere at Neopax wrote:


I am building an experiment. Does anybody know what blocks a
magnetic field?


Why do people post their physical questions to sci.chem? Chemistry is
the science about substances changind into other substances.


Like nuclear chemistry?


Are you bored? So tell me what chemistry is. And if blocking a magnetic
field is likely part of that.

Well, I could argue that there is no such thing as chemistry, merely low energy
physics.

Hee hee.

Please do so argue, that there is no such thing
as chemistry, merely low energy physics.


Mark (Statistically, physicists are more likely
to be mentally ill; chemists, drunks :-)

Subject: Does anybody know what blocks a magnetic field?
From: (Mark Tarka)
Date: 6/27/2004 1:00 PM Pacific Standard Time
Message-id:

Dirk Bruere at Neopax wrote in message
...
Bernhard Kuemel wrote:

Dirk Bruere at Neopax wrote:


I am building an experiment. Does anybody know what blocks a
magnetic field?

Nothing, otherwise a perpetual motion machine could be invented--or we could
get energy for nothing.

In article ,
Mark Tarka wrote:
Dirk Bruere at Neopax wrote in message
...
Bernhard Kuemel wrote:

Dirk Bruere at Neopax wrote:


I am building an experiment. Does anybody know what blocks a
magnetic field?


Why do people post their physical questions to sci.chem? Chemistry is
the science about substances changind into other substances.

I don't know why they ask those types of questions in sci.chem, but I do
know what blocks a magnetic field. (Posting from sci.physics.)

It matters whether it's a static field or a changing field. Assuming
static, the traditional method is a Helmoltz coil-- two large-diameter
solenoids separated by the same distance as their radii, with the current
adjusted to cancel the field in the middle. The coils must be oriented
properly. Or other arrangements of compensating coils can be used.

The other way is with magnetic shielding, which is material with a high
permeability. Iron can help, but it's not very good. Mu-metal, a
nickel-iron alloy with around 60% nickel, is much better, but expensive.
Even better, but still more expensive, are the more exotic alloys like the
amorphous MetGlas ribbons. Multiple thin shells work better than a thick
shell. After constructing the shielding it must be annealed to eliminate
stresses that create fields, and it should be degaussed before use. When
holes are needed, many small holes are better than one big hole, and
little chimneys on the holes will improve the shielding.

Solenoids and permeable materials are sometimes used in combination, e.g.
to null out fields that leak in through the holes. Or a long shell that
tends to align any field down the pipe, and solenoids to null it out.

If shielding changing fields, non-magnetic conducting materials like
aluminum become useful.

Mark (Statistically, physicists are more likely
to be mentally ill; chemists, drunks :-)

I was not aware of that.

--
"Outside the camp you shall have a place set aside to be used as a
latrine. You shall keep a trowel in your equipment and with it, when you
go outside to ease nature, you shall first dig a hole and afterward cover
up your excrement." -- Deuteronomy 23:13-14

Gregory L. Hansen wrote:

Mark Tarka wrote:


Dirk Bruere at Neopax wrote in message


Bernhard Kuemel wrote:


Dirk Bruere at Neopax wrote:


I am building an experiment. Does anybody know what blocks a
magnetic field?


Why do people post their physical questions to sci.chem? Chemistry is
the science about substances changind into other substances.



I don't know why they ask those types of questions in sci.chem, but I do
know what blocks a magnetic field. (Posting from sci.physics.)

Since a number of us who read sci.chem have experience in this area.

It matters whether it's a static field or a changing field. Assuming
static, the traditional method is a Helmoltz coil-- two large-diameter
solenoids separated by the same distance as their radii, with the current
adjusted to cancel the field in the middle. The coils must be oriented
properly. Or other arrangements of compensating coils can be used.


Generally three pairs of Helmholtz coils oriented along three mutually
perpendicular directions. I once beat out the Earth's field to a part
in 100000 over about a 10 cm cube with some large coils. We were able
to do NMR down to about 60 or 70 gauss using a Pound box in that volume.
Had I been a chemist at that point I might have become rich and famous

josh halper

Led

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