  We study a generalization of Aharonov-Bohm effect, the potential effect. The
discussion is focused on field-free effects in simply connected region, which
obviously can not have any local field-flux. Among the published discussions
about this kind of effects, it is generally agreed that this kind of effects
does not exist due to gauge invariance. However, there are also opinions that
this effect is a trivial variation of Aharonov-Bohm effect and therefore there
is no need to check its existence. To my knowledge, it has never been tested.
My first goal here is to supply enough theoretical reason to motivate the
experimental test of this effect. I start with an intuitive derivation, then I
introduce a wave-front theory as a theoretical consideration. Logically, the
existence of potential effect implies the existence of the AB effect, but not
vice versa. The purpose of this paper is to provide a physical connection in
the opposite direction.
