(* Coulomb repulsion between two charges seen also through the FIELD argument *) F[x_,y_]=((x-x1) (x-x2)+(y-y1) (y-y2))/ (Sqrt[(x-x1)^2+(y-y1)^2]^3 Sqrt[(x-x2)^2+(y-y2)^2]^3) (x - x1) (x - x2) + (y - y1) (y - y2) ----------------------------------------------------- 2 2 3/2 2 2 3/2 ((x - x1) + (y - y1) ) ((x - x2) + (y - y2) ) x1=0; y1=0;x2=4; y2=0; Plot3D[F[x,y],{x,-3,7},{y,-5,5},PlotPoints ->40]; DensityPlot[F[x,y],{x,-3,7},{y,-5,5},PlotPoints ->40]; (* DensityPlot[f, {x, xmin, xmax}, {y, ymin, ymax}] makes a density plot of f as a function of x and y. *) (*Plot3D[F[x,y],{x,-3,7},{y,-5,5},PlotPoints ->40];*) Plot[F[x,0],{x,-3,7}, PlotRange->{-0.2,0.5}]; Plot[F[x,0.5],{x,-3,7}, PlotRange->{-0.2,0.5}]; Plot3D[F[x,y],{x,-3,7},{y,-5,5},PlotPoints ->40,PlotRange->{-0.15,0.15}] DensityPlot[F[x,y],{x,-3,7},{y,-5,5},PlotPoints ->40,PlotRange->{-0.15,0.15}] ContourPlot[F[x,y],{x,-3,7},{y,-5,5},PlotPoints ->40,PlotRange->{-0.15,0.15}] ContourPlot[F[x,y],{x,-3,7},{y,-5,5},PlotPoints ->80, PlotRange->{-0.15,0.15},ContourShading->False, ContourSmoothing->Automatic] Show[Plott]