In recently reading Halliday, Resnick, & Walker, I was alarmed to read
"We have already seen that matter, energy and angular momentum are
quantized; [electric] charge adds one more important quantity to the list."
Earlier in the book, one can find "Yet on a fine enough scale, air is not
continuous at all but comes in ... particles of specific masses ... . We
say that mass is quantized."
This seems to me to be a very muddled idea of quantization. Consider:
- Mass is 'quantized' in the sense that it is made up of discrete
particles. But as far as I know there is no way to index allowed masses,
unless the system has only one atomic species.
- Energy is 'quantized' in any *specific* system, and the allowed energies
can be indexed. However, for any energy you might choose, you can find a
system in which that energy is allowed.
- Charge is 'quantized' everywhere, always.
Personally, of the three I would only say that "charge is quantized", since
such a statement seems to imply some sort of universality. In a particular
system, I would say the energy is quantized *by the potential*. I would
never say that mass is quantized; I would say that it is made up of
particles. In any case, I *certainly* would never say "Charge is
quantized, just like energy and mass;" those different cases aren't very
similar.
How does everyone else feel about this. Am I expecting too much precision
in the language? Is there a deep, theoretical sense in which these cases
*are* similar? Or is this another entry for the text book misconceptions
list?
--
--James McLean
jmclean@chem.ucsd.edu
post doc
UC San Diego, Chemistry