[BC] Aluminum and magnetic/electric currents (was KSDK)

[Sherrod Munday]

On Tuesday 31 January 2006 08:14, WFIFeng at aol.com wrote:
> Even aluminum will react to a powerful enough, fluctuating magnetic field.
> With a powerful magnet, you can feel this effect- get a magnet from a
> defunct hard drive, and slide it quickly over an aluminum plate. You will
> feel a very distinct resistance which increases as you move the magnet
> faster. You can also feel it if you have a bulk tape eraser. Bring that
> aluminum plate close to the field, and you will feel the magnetically
> induced vibration in it.

Back in college, a Physics (Materials in Science) teacher was demonstrating 
superconducting properties and principles and how they relate to materials, 
and had some liquid hydrogen (or similar supercooled liquid).  He had a plate 
of aluminum attached to the bottom of a pendulum arm that swung between two 
magnets (spaced apart enough to allow the plate to travel freely between 
them) mounted at the bottom of the arc of the pendulum arm.

With the aluminum plate at normal room temperature, the pendulum oscillated 
back and forth rather freely between the magnets, coming to rest under the 
effect of normal friction and gravity.

He then placed the aluminum in the liquid to supercool it, and then put it 
back on the pendulum.  When it swung from full height down and came in 
between the magnets, it stopped.  Dead.  No hysteresis, no ringing, no 
further movement.  

As he explained, at supercooled temps. the movement of the conducting material 
(aluminum) through a magetic field induces an electrical current that in turn 
produces a magnetic field that then interacts with the normal magnetic field 
of the magnets, causing the plate to stop moving.  Even though Al is not 
ferrous, the movement of it through a magnetic field does produce electric 
currents (just like copper) that can interact with its surroundings.  
Supercooling it makes the resistance of the current flow so low that a real 
magnetic field can be generated, whereas the resistance at normal room temps 
is enough to suppress the magnetic fields to the point where they are not a 
significant factor in causing the plate to stop swinging.
-- 
Sherrod Munday <smunday at srnradio.com>
Technical Director
Salem Radio Network    (972) 831-1920