electric  field   The force which a point charge q' experiences when  it  is  in the vicinity of another point charge q is due to the  electric field of the charge q. If F is the force on q', we define the electric field, E through the equation

F = q' E

From Coulomb's Law*, the electric field strength (in vacuum) is

given by,

E = [1/(4 p e ₀)] [q/ r²] r_u

where r is the distance between q and q', and r_u the unit vector along r.