Date: Fri, 14 Nov 2003 17:22:35 -0600
Reply-To: Wesley Alden Pegden <wes@CS.UCHICAGO.EDU>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Wesley Alden Pegden <wes@CS.UCHICAGO.EDU>
Subject: Re: Fwd: RE: "Green" solar battery charger (NO VANAGON CONTENT)
In-Reply-To: <vanagon%2003111322305962@GERRY.VANAGON.COM>
Content-Type: TEXT/PLAIN; charset=US-ASCII
yo,
Motion in complete agreement with Newton's laws? Boy, Einstein would have
a word with you! ;). That Einstein's theories of special and general
relativity are "more correct" than Newton's laws is well known and agreed
upon among scientists. On the other hand, people have known for hundreds
of years that Newton's laws weren't explaining everything (the orbit of
mercury, for example, precesses in a way which is completely mysterious in
light only of Newtonian mechanics). Of course, this doesn't stop people
from calling it a "law". In fact, I'd argue that in the case of MOST
scientific theories (and 'laws'), scientists generally believe that they
AREN'T the complete picture. Ohm's law and Newton's laws, (and
certainly, Einstein asserted many times, Relativty as well), are different
approximations of how things actually behave.
Just my friendly rant on science!
-wes
'84 vanagon, getting a new master cylinder
On Thu, 13 Nov 2003, 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).
>
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