Electric Field
The field strength should depend on the charge or charges that set it up. The force depends on the field set up by those charges and the amount of charge of the particle at that point in space (in the field):
Fon 2 = q2 * Efrom 1 (like Fgr = m*g)
or, Efrom 1 = Fon 2 / q2 .
Note that since F is a vector and q is a scalar, E must be a vector.