Chronology Current Month Current Thread Current Date [Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-L] standard dc circuits

It is amusing to couch the question in terms of the highly unfashionable hydraulic model analogy, so that I would be asking this: if I plumb a water pump to a constriction, then to two branch constrictions of equal aperture, how is it that the pump output pressure field motivates a flow of one cc per second through the first constriction and a flow of 0.5 cc/sec though each of the two following constrictions?

An hydraulic Emeritus Professor might then say: The applied water pressure is measurable along the surfaces of the various pipes and the pressure field can be calculated at the input and exit of each constriction.

I might then continue: the pressure difference across each constriction may be varied widely, subject only to the constraint that the pressure difference across the first constriction added to the pressure difference across the succeeding two constrictions cannot exceed the pressure difference across the pump outlet to inlet.

But then, I suppose I would be blurring the distinction between longitudinal pressure transmission and pressure transmission by means of a transverse effect??? : -)

Brian Whatcott Altus OK

On 11/22/2013 1:26 PM, Bob Sciamanda wrote:
It might help to realize that the fields are produced by charges which accumulate on wire surfaces AND wherever there is a change in conductivity, eg at resistor terminals.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
http://mysite.verizon.net/res12merh/

-----Original Message----- From: Paul Lulai
Sent: Friday, November 22, 2013 2:11 PM
To: Phys-L@Phys-L.org
Subject: [Phys-L] standard dc circuits

I have a question about the junction rule for simple dc circuits.
I have a battery connected to 1 lamp, then split to 2 lamps in parallel and back to the battery.
For easy numbers, if 1 amp flows through the first lamp, then 0.5 amps flow through each lamp in parallel (if all lamps are ideal).
Using the junction rule, I know that current into each junction or node must equal the current out of each junction or node. It is simply a conservation of charge in that area.
How does that reconcile with a fields approach? I might have some incorrect notions below. I am open to correction.
The batteries produce a field that move charges already present in the wire. If all wires are of the same material, diameter, length (and so on) why is the current less in the parallel branches than in the wires before and after the parallel branch? Does something make the field in the parallel branches smaller than the field in the series portion before and after the parallel branch? I don't see it.
Thanks for any input.
Paul.

_