Re: Expressing fractions

From: Mike Lyle (mike_lyle_uk_at_REMOVETHISyahoo.co.uk)
Date: 01/08/05 

Date: Sat, 8 Jan 2005 21:46:14 -0000

Don A. Gilmore wrote:
> "Lee Sau Dan" <danlee@informatik.uni-freiburg.de> wrote in message
> news:87sm5bdboq.fsf@informatik.uni-freiburg.de...
>>>>>> "Don" == Don A Gilmore <eromlignod@kc.rr.com> writes:
>
> Don> Well, it's really complex to figure out. Steel is
basically
> Don> about twelve times more resistive than copper, but you
must
> Don> take into account the diameters, the contact between the
coil
> Don> and the core and the contact between coils.
>
> Don> My latest theory is that the axis of the copper, while not
> Don> the only path, is a solid, attractive path for a majority
of
> Don> the electrons. In addition to increased resistance
because
> Don> of the length of the wire, the circular flow could cause
eddy
> Don> currents in the core, further heating it. Hell, I don't
> Don> know.
>
>> When copper is in contact with iron, the iron rusts first. When
>> the iron rusts out, then the copper rusts. This is called
>> preferential rusting (or something like that).
>
>
> It's called "galvanic corrosion". Steel is higher (more anodic)
than
> copper in the galvanic series, so an electrochemical cell could
cause
> corrosion of the steel. But this only occurs appreciably when the
> metals are exposed to a conducting liquid electrolyte, like sea
water.
>
>
>> When metals are in contact, the
>> most reactive one rust first, leaving the others intact. Indeed,
>> with this setting, the rusting of that most reactive metal goes
>> faster than when this metal isolated from the others. This
has
>> bad impact on metal-metal junctions connected by soldering
>> material that is less reactive. But the good point is that you
>> can prevent a metal from rusting by keeping it in touch with a
>> more reactive metal (e.g. iron protected by magnesium). This is
>> called sacrificial rusting (of the more reactive metal).
>> Connecting the metal to the cathode of a battery also does
>> the trick. (That's how a car's metal shell is protected from
>> rusting. If the battery runs out, then the will begin to rust.
>> So, keep the battery charged!)
>> I don't know what kind of steel you have in your guitar
>> string. Stainless steel are naturally protected by a thin and
>> transparent and hard layer of rust of chromium, which protects
the
>> steel inside from further rusting. Not sure if this
protective
>> coating has good conductivity. (You can't remove the
coating
>> by scratching the stainless steel surface, as the exposed metal
>> contains chromium, which rusts immediately to form a new
protective
>> layer.) But it can prevent the steel from rusting, hence leaving
>> the copper vulnerable.
>
>
> Piano strings are made from a very high tensile strength,
high-carbon
> steel (called "music wire"). They are never stainless steel. The
> copper windings are bare copper. They last a very long time
(pianos
> over 100 years old are commonplace) and experience very little
> corrosion, though it is sometimes more pronounced if you live near
> the ocean.
>
> Now all I have to do is figure out what your comments have to do
with
> the resistance of the string.
>
> Don
> Kansas City

You never heard of electric pianos, then?

Mike.

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