Note that E is the fi field produced by some charge or charge distribution eld separate fr from om
the test charge —it is not the fi field produced by the test charge itself. Also, note that the
eld existence of an electric fi field is a property of its source eld —the presence of the test charge
is not necessar necessary for the y fi field to exist. The test charge ser eld serves as a ves detector of the electric
fi field. eld.
Equation 23.7 can be rearranged as
23.1 Particles Only
articles Equation 23.8 is only valid for a
charged par particle ticle—an object of
zero size. For a charged object of