Ask A Scientist Physics Archive

name         James K.
status       student
age          30s

Question -   Is there a substance that can block magnetic force and
act as a shield (such as Nu-Metal or soft iron), but which, unlike these
two substances is not affected itself by the magnet.  For example, wood
is not affected, by a magnet but unfortunately, it is not an effective
shield.  Is there a substance that can act as a shield but also be
unaffected (ie. not attracted to the magnet)?
----------------------------------------------------------
James,
There is not such a material.  If you explore the field of magnetism, you
will discover something called Ampere's Law.  The source of magnetic field
is moving electric charges, either through a circuit or around an atom.  The
only way to shield a magnetic field is to provide electric charges moving in
the opposite direction.  These two set of moving charges will feel magnetic
force between each other.

One example of such a device is coaxial cable:  one cable formed as a
cylinder around another.  The current of one cable is exactly opposite that
of the other.  Each produces a magnetic field, but the fields cancel each
other outside the outer cable.  There is a very magnetic field between the
cables.  Because of the circular geometry, everything is symmetric.  The
inner cable is pulled outward in all directions, and the outer cable is
pulled inward.  After all is said and done, it works out to be a very useful
and reliable piece of equipment.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
=============================================================================