It is precisely here that the
notion of electric field (strictly, electromagnetic field) is natural and very
useful The field picture is this: the accelerated motion of charge q1
produces electromagnetic waves, which then propagate with the speed
c, reach q2 and cause a force on q2 The notion of field elegantly accounts
for the time delay Thus, even though electric and magnetic fields can be
detected only by their effects (forces) on charges, they are regarded as
physical entities, not merely mathematical constructs