' - - Electric Force :  2 Charges

qa = 5  :  xa = 2  :  ya = 2 
qb = -5 :  xb = -2 :  yb = -2

Ra{x,y} = Sqrt[(x - xa)^2 + (y - ya)^2]
Rb{x,y} = Sqrt[(x - xb)^2 + (y - yb)^2]

Ex{x,y} =  qa*(x - xa)  / Ra{x,y}^3  +  qb*(x - xb)  / Rb{x,y}^3
Ey{x,y} =  qa*(y - ya)  / Ra{x,y}^3  +  qb*(y - yb)  / Rb{x,y}^3

a = -5  : b = 5 : n = 10
c = -5 : d = 5 : m = 10

PlotDirField[Ex, Ey, {a,b,n}{c,d,m}]

' Use Shift-S to increase the vector lengths.

