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Date:         Thu, 13 Nov 2003 19:05:38 -0800
Reply-To:     Jack <john.cook58@VERIZON.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jack <john.cook58@VERIZON.NET>
Subject:      Re: Fwd: RE: "Green" solar battery charger
Comments: To: "Daniel L. Katz" <katzd54@YAHOO.COM>
In-Reply-To:  <vanagon%2003111317085685@GERRY.VANAGON.COM>
Content-type: text/plain; charset=US-ASCII

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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