What this means is that the actual value
of potential energy is not physically significant; it is only
the difference of potential energy that is significant We can
always add an arbitrary constant a to potential energy at
every point, since this will not change the potential energy
difference:
(
)
(
)
P
R
P
R
U
U
U
U
α
α
+
−
+
=
−
Put it differently, there is a freedom in choosing the point
where potential energy is zero A convenient choice is to have
electrostatic potential energy zero at infinity With this choice,
if we take the point R at infinity, we get from Eq