Re: Battery connection

[Bernard Cleyet <anngeorg@PACBELL.NET>]

different, not very, at least in the example I chose to measure:

Two AA alkaline made for Kodak (only clue to mfg. is Jap. [with the
period it's not racist.] pictographs) as supply "charging" a third; the
internal R is 0.21 Ohms.  Discharging the same cell, it's 0.26 -- this
diff. is 3 X the difference between two trials in the charging mode.
Before making any grandiose claims, I 'd want to do more trials.  Next
time I'll use a regulated supply to do the charging.  I suspect in the
case of secondary cells there is a smaller diff..

bc

P.s. I used four resistors (16, 42, 62 and 196 Ohms) in both configs..
Two inexpensive R/S DMM (1%), and Graphical Analysis (Vernier) to do the
regression.  Their COR was > 0.999, charge and > 0.998, discharge.

Ludwik Kowalski wrote:

> 1) brian whatcott wrote:
>
> > Sometimes, the internal resistance of cells and batteries of cells
> > is unimportant: this time though, it matters.
> >
> > We suppose that the internal resistance R is proportional to its
> > terminal voltage - for no very fundamental reason, save that the
> > battery of two cells may be using the same type cell as the single
> > cell. ...
>
> Brian referred to a situation in which a lower V battery is a
> load for a higher V battery. Is the resistance presented by a
> battery when it is used as a load the same as when it is used
> as a source? I suspect it is very different. But I am not sure.
>
> 2) I am always puzzled by battery cells. Most introductory
> physics texts describe their electrical properties. Chemical
> reactions taking place in some cells are also described,
> occasionally. But all this seems to be a description of what
> happens rather than an explanation of why it happens.
> I suspect that many on this list would appreciate if
> somebody could post a short essay about batteries for an
> elementary physics course.
>
> My impression is that electochemical cells can not be explained
> at the elementary level; they are what they are; period. Am I the
> only one to think this way? [Using big words, like Gibbs
> potential, QM or double layer, does not contribute to clarity
> at the level of my teaching.]
> Ludwik Kowalski