Mitchell Institute for Fundamental Physics & Astronomy
College Station, Texas 77843
We all use batteries constantly, but the usual discussion in physics textbooks — where one would expect to learn about voltaic cells, which in parallel and/or series combination constitute batteries — leaves many unresolved questions:
(1) no real discussion of emf and why small AAA cells have the same emf as much larger A cells;
(2) no discussion of how chemistry produces the emf, and that there are two distinct electrodes;
(3) the false impression that the emf occurs within the volume of the cell;
(4) no discussion of chemical “charge” and energy storage;
(5) the imaginary dotted box drawn around the voltage source and “internal” resistance;
(6) no discussion of the differences between fast charge and discharge, and slow charge and discharge;
(7) 100-1000x too large internal resistances for the typical car-starting battery.
Eventually I resolved these questions to my satisfaction, and last year I published a related paper in the Physics Teacher (see title of talk). In addition to resolving these questions, it also discusses:
(A) the different definitions of cathode and anode used by battery-ists, chem-ists, and physic-ists;
(B) the distinction between “charge” and “surface charge”;
(C) Why Faraday is Good, Volta is Bad, and Galvani is downright Ugly.
Because figures (including a fictional one of a young Feynman in a slowly-emptying bathtub) will mostly replace equations, I will try to finish early and then open up for questions from the audience.