  We discuss several aspects of particle production in: (a) time dependent
electric field and (b) expanding Friedmann background. In the first part of the
paper, we provide an algebraic mapping between the differential equations
describing these two phenomena. This mapping allows a direct comparison between
(a) and (b) and we highlight several interesting features of both cases using
this approach. We determine the form of the (equivalent) electric field
corresponding to different Friedmann spacetimes and discover, for example, a
time-dependent electric field which, in a specific limit, leads to a Planck's
spectrum of particles. We also discuss the conditions under which the particle
production in an expanding background will be non-analytic in the parameter
which encodes the coupling to the curved spacetime, in close analogy with the
generalized Schwinger effect. In the second part of the paper, we study the
situation in which both time dependent electric field and an expanding
background are simultaneously present. We compute particle production rate in
this context by several different methods paying special attention to its
limiting forms and possible non-analytic behaviour. We also clarify several
conceptual issues related to definitions of in-vacuum and out-vacuum in these
systems.
