Date: Fri, 14 Nov 2003 00:17:10 -0500
Reply-To: "Daniel L. Katz" <katzd54@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "Daniel L. Katz" <katzd54@YAHOO.COM>
Subject: Re: Fwd: RE: "Green" solar battery charger
tom:
let's see, speaking as a practical vanagon man:
(1) if you apply 1 V across the high tension side of a vanagon ignition
system you get zero spark current with 1 V applied across the spark gap.
apply 10,000 V, and a spark current developes, and the resistance across
the gap drops from infinity to probably a few hundred ohms at the peak of
the spark current, while the voltage across the gap drops, respectively,
from 10,000 V to a roughly a few to several tens of volts (with most of
the voltage drop across the coil secondary, and coil and plug wires).
complicated. the resistance of the spark gap itself depends on the current
flowing, temperature, pressure, and other factors. ohms law doesn't apply
to gaseous conduction.
what about the resistance of a copper wire carrying a spark current? even
ignoring reactive effects, since the current is pulsed, the the effective
cross sectional area of the wire is reduced by the skin effect in a
complicated time varying manner.
then we have our coolant level electrodes. note that that system uses AC
as a dodge around the failure of ohms law for DC.
diodes are useful because they don't obey ohms law.
many things on our vans operate outside of ohms law, but none outside of
newton's laws.
dlk
On Thu, 13 Nov 2003 22:05:48 -0600, tom ring <taring@TARING.ORG> wrote:
>Uh, sorry, Ohm's law works. And it is a law. Just like Kirchoff's. No
>qualifications at any reasonable level of detail until you get to the
quantum
>mechanical level, and that's not applicable to anything this group would
>experience. AMD and Intel chip engineers maybe are getting near there,
but not
>us.
>
>And Newton's work fine until you speed things up, a lot.
>
>tom
>
>On 13 Nov 2003 at 22:27, Daniel L. Katz wrote:
>
>> jack:
>>
>> ohm's law really isn't a law, in the sense that newton's laws, for
>> example, are physical laws. that is, if motion is studied in finer and
>> finer detail, the limit is complete agreement with newton's laws. on the
>> other hand, if current in a resistor is studied with increasing detail,
>> the picture gets more and more complicated, with all kinds of
empirically
>> determined parameters, and so on.
>>
>> dlk
>>
>> On Thu, 13 Nov 2003 19:05:38 -0800, Jack <john.cook58@VERIZON.NET>
wrote:
>>
>> >re: "... ohm's law implies that a current of 12 V/300 Ohm = 0.04 A
>> >will flow ..."
>> >
>> >No! It doesn't "imply". It's the LAW!
>> >
>> >Sorry. Couldn't resist.
>> >
>> >//Jack
>> >
>> >
>> >On 13 Nov 2003, at 16:59, Daniel L. Katz wrote:
>> >
>> >> list:
>> >>
>> >> kindly note that current and voltage are not independent, and that
100
>> mA
>> >> through the heart for 1 s would probably be fatal.
>> >>
>> >> in the simplest cases, current and voltage are related fairly
precisely
>> >> through ohm's law:
>> >>
>> >> I = V/R
>> >>
>> >> where I = current and V = potential difference across R. for example,
>> if 12
>> >> volts is applied across a 300 ohm 1 W resistor, ohm's law implies
that a
>> >> current of 12 V/300 Ohm = 0.04 A will flow through the resistor. it
>> makes no
>> >> difference whether we say the voltage is 12 V on one side of the
>> resistor and
>> >> 0 volts on the other, or 1,000,012 volts on one side and 1,000,000
>> volts on
>> >> the other, we get the same 12 V potential difference across the
>> resistor, and
>> >> the same amount of current, 0.04 A, will flow. in this case, the
power
>> >> developed by the resistor would be 0.48 watts, within its 1 W power
>> rating.
>> >> now, what if we substitute a 30 ohm 1 W resistor instead? well ohms
law
>> would
>> >> predict a 0.4 A curren and heat produced at the rate of 4.8 W,
nearly 5
>> times
>> >> the power rating of the resistor; in this case, ohm's law does its
job
>> in so
>> >> far as letting us know that the resitor would fry, but the resistor
>> itself
>> >> would change value significantly as it burned up.
>> >>
>> >> dlk
>> >>
>> >>
>> >>
>> >> >The charge LED flashes fine even in pretty low light, but it's only
>> >> >indicating that there's voltage present... however there's nearly no
>> >> >current, and it's current, not voltage, which will charge a
>> >> >battery... or an electrocution! (a 100mA current of 1,000,000V will
>> >> >not even be felt).
>>
>
>
>------
>Tom Ring K0TAR, ex-WA2PHW EN34hx
>85 Westphalia GL Albert
>96 Jetta GL The Intimidator
>taring@taring.org
>
>"It is better to go into a turn slow, and come out fast, than to go into
a turn fast
>and come out dead." Stirling Moss
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