First, we assume
that the test charge q is so small that it does not disturb
the original configuration, namely the charge Q at the
origin (or else, we keep Q fixed at the origin by some
unspecified force) Second, in bringing the charge q from
R to P, we apply an external force Fext just enough to
counter the repulsive electric force FE (i e, Fext= –FE) This means there is no net force on or acceleration of
the charge q when it is brought from R to P, i