Message-Id: <l03110714b3551c1b73c6@[192.174.2.173]>
In-Reply-To: <199905041947.MAA04748@noontide.lick.pvt.k12.ca.us>
Date: Tue, 4 May 1999 14:01:03 -0800
To: "Pinhole Listserv" <pinhole@exploratorium.edu>
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole Mars Magnetism with picture pointer
Hi Sarah
You cannot use ohm's law for superconductors since the resistance is zero.
Your students should get R = 0 when they calculate R=pL/A since the
resistivity p=0.
You have to treat the superconducting wire as an inductor with inductance
instead of as a resistor. When you apply a voltage the current starts at 0
and grows linearly with time. The current builds a magnetic field around
the wire. The growing magnetic field opposes the changing flow of current
(inductance).
Paul Doherty
Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld