From: Paul Doherty (pauld@exploratorium.edu)
Date: Sat Nov 20 1999 - 15:48:08 PST
Message-Id: <l03110711b45ce28850fb@[192.174.2.173]> Date: Sat, 20 Nov 1999 15:48:08 -0800 From: Paul Doherty <pauld@exploratorium.edu> Subject: Re: pinhole Mars Magnetism with picture pointer
Hi Sarah
For definitions of resistance R = V/I is the definition.
However resistance deals only with the DC portion of electric current,
other terms must be used for AC.
However for a superconductor R is essentially 0. So you can get a huge
current with a small voltage.
However for a superconductor there are other reasons that the current does
not become infinite, the current starts out as 0, when you apply a voltage
the current must change so you have to bring in the inductance of the wire
which stops the change of electric current. As a result when you apply a
voltage to a superconductor the current grows linearly as the magnetic
field grows around the wire. The growing magnetic field resists the
increase of the current.
You's have to send me the resistivity the students were using so I could
check their results. I believe that the resistance calculated via
resistivity should give a value near 0.
Paul D
Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld
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