  The effects of an external field on the dynamics of chiral symmetry breaking
are studied using quenched, ladder QED as our model gauge field theory. It is
found that a uniform external magnetic field enables the chiral symmetry to be
spontaneously broken at weak gauge couplings, in contrast with the situation
when no external field is present. The broken chiral symmetry is restored at
high temperatures as well as at high chemical potentials. The nature of the two
chiral phase transitions is different: the transition at high temperatures is a
continuous one whereas the phase transition at high chemical potentials is
discontinuous.
