Re: [Phys-l] battery redux and again (part deux)

[John Denker <jsd@av8n.com>]

On 02/28/2007 02:05 PM, fizix29@aol.com wrote:

> My question is simply what is the mechanism in a real chemical battery which transports the
> charge against the electric field?

1) The microscopic mechanisms inside batteries are insanely complicated
 and tricky.  Really understanding it would probably be a tour-de-force
 of chemistry and condensed-matter physics.

 I say "probably" because I've never seen it done.

 Here are some modest efforts of mine, which say a few things about
 the structure and strategy of batteries ... but which may leave you
 with as many questions as answers:
   http://www.av8n.com/physics/battery.htm
   http://www.av8n.com/physics/lead-acid.htm

 This afternoon I revised the "battery" document and greatly upgraded
 the figures.

 All the gen-ed textbook discussions I've seen are provably nowhere
 close to being correct.  For starters, most of them show the electric
 field in the middle of the electrolyte compartment going the wrong way.

 I've read some of the engineering literature, and it has remarkably
 little to say about the microscopics.

2) It is amusing in a macabre way to read the textbook "mechanical"
 analogies of how a battery works, based on VdG generators and such.

 One big problem is that most students have no clue about the microscopic
 phenomena involved in static electricity.  Therefore the any such
 mechanical model of a battery contravenes the rule that "learning
 proceeds from the known to the unknown".

 As a pedagogical suggestion, I would suggest figuring out how
 electrostatic generators work ... not because they directly
 provide a good model for batteries -- which they don't -- but they
 are interesting unto themselves, and they lay some useful general
 groundwork concerning work functions, dipole layers, and suchlike.