  The effects of charge exchange on waves propagating in weakly ionized plasmas
are discussed. It is shown that for low-frequency processes, ions and neutrals
should be treated as a single fluid with some effective charge on all of them.
We have derived a new momentum equation which should be used in such an
environment. As a result, the low-frequency magnetic waves can propagate even
if particles are not magnetized, which is entirely due to the charge exchange
and the fact that it is not possible to separate particles into two different
populations as charged and neutral species. So there can be no friction force
between ions and neutrals in the usual sense. The mean force per particle is
proportional to the ionization ratio $n_i/(n_i+ n_n)$. Regarding the
application of the theory to the Alfven wave propagation in the lower solar
atmosphere, the results predict that the plane of displacement of the fluid
must change by 90 degrees when an Alfven wave propagates from the area where
particles are un-magnetized (photosphere) to the area where they are magnetized
(chromosphere). Because of the most accurate cross sections which we have here,
it is possible to very accurately determine altitudes at which such rotation of
the Alfven wave takes place.
