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Re: Floppies - Actual Question

From	ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups	comp.os.linux.misc
Subject	Re: Floppies - Actual Question
Date	2025-10-06 10:29 +0000
Organization	Stefan Ram
Message-ID	<cage-20251006112530@ram.dialup.fu-berlin.de> (permalink)
References	(4 earlier) <10b1krp$3tbca$4@dont-email.me> <mjjf90Ftbb2U5@mid.individual.net> <slrn10d943v.aj5.spamtrap42@one.localnet> <r7kfqlxilj.ln2@Telcontar.valinor> <10b4ekb$jqe8$5@dont-email.me>

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Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> wrote or quoted:
>On Thu, 25 Sep 2025 13:04:59 +0200, Carlos E.R. wrote:
>>At some point in the 80's, a friend at uni wanted to go home with his
>>floppies kept safe (the train was electric). We told him to try wrapping
>>in aluminum kitchen foil, or perhaps in a cookie tin box. I don't
>> remember what he did exactly, but it worked.
>“Faraday cage”.

  In a perfect conductor, inside the material itself (such as
  the cage walls), the electric field E is zero because free
  charges move to cancel any applied electric field.

  Faraday's law then implies that within the conductor, the magnetic
  field B cannot be changing with time.

  Changing magnetic fields induce currents (eddy currents).
  These induced currents generate opposing magnetic fields
  that cancel the time-varying components inside the conductor,
  effectively shielding against changing magnetic fields.

  But this does not imply zero magnetic field inside the conductor's
  hollow interior (the cage's interior space). Static fields do not
  induce currents because there is no changing magnetic flux within
  the conductor to generate an electromotive force. Consequently,
  these magnetic fields penetrate the cage interior unaffected.

  Also, real materials might not be perfect conductors. And it
  seems that, in practice, a Faraday cage can possibly protect
  to some extend against fast changing magnetic fields, but less 
  against slowly changing magnetic fields.

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Thread

Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-25 22:10 +0000
  Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-25 21:09 -0400
  Re: Floppies - Actual Question ram@zedat.fu-berlin.de (Stefan Ram) - 2025-10-06 10:29 +0000
    Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-06 22:08 +0000
    Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-06 23:30 -0400
      Re: Floppies - Actual Question Rich <rich@example.invalid> - 2025-10-07 15:16 +0000
        Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-08 02:34 +0200
          Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-08 01:05 -0400
            Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-08 10:58 +0200
              Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-08 11:06 +0100
              Re: Floppies - Actual Question ram@zedat.fu-berlin.de (Stefan Ram) - 2025-10-08 12:10 +0000
                Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-08 14:14 +0200
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:44 -0400
                Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-09 21:10 +0200
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 21:36 -0400
                Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:54 +0100
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 01:57 -0400
                Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-10 13:49 +0200
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 02:29 -0400
                Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-11 14:32 +0200
                Re: Floppies - Actual Question Joerg Walther <joerg.walther@magenta.de> - 2025-10-09 12:50 +0200
                Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-09 21:11 +0200
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 21:37 -0400
                Re: Floppies - Actual Question Joerg Walther <joerg.walther@magenta.de> - 2025-10-10 11:19 +0200
                Phone wallet "Carlos E.R." <robin_listas@es.invalid> - 2025-10-10 13:51 +0200
                Re: Phone wallet c186282 <c186282@nnada.net> - 2025-10-11 02:30 -0400
                Re: Phone wallet "Carlos E.R." <robin_listas@es.invalid> - 2025-10-11 14:32 +0200
                Re: Phone wallet c186282 <c186282@nnada.net> - 2025-10-11 21:35 -0400
                Re: Phone wallet "Carlos E.R." <robin_listas@es.invalid> - 2025-10-12 14:48 +0200
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 21:17 -0400
                Re: Floppies - Actual Question Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-10-10 06:51 +0000
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-10 03:29 -0400
                Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:55 +0100
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 02:10 -0400
                Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-08 13:18 +0100
                Re: Floppies - Actual Question Robert Riches <spamtrap42@jacob21819.net> - 2025-10-09 03:09 +0000
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:58 -0400
                Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-09 12:45 +0100
                Re: Floppies - Actual Question Robert Riches <spamtrap42@jacob21819.net> - 2025-10-10 02:53 +0000
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 23:44 -0400
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:45 -0400
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:38 -0400
                Re: Floppies - Actual Question Rich <rich@example.invalid> - 2025-10-09 15:16 +0000
                Faraday cages (was: Re: Floppies - Actual Question) Nuno Silva <nunojsilva@invalid.invalid> - 2025-10-09 17:02 +0100
                Re: Faraday cages Rich <rich@example.invalid> - 2025-10-09 18:48 +0000
                Re: Faraday cages The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:49 +0100
                Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:47 +0100
                Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 01:05 -0400
          Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-08 01:52 -0400
        Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-08 01:38 -0400

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