Actually this is an home work problem....we dont solve your home work problems.......As you have asked to give some insight and not demanded a code....I wanted to help you. I h ave quickly typed a code......your code should be more or less like this. Go throught the code , understand it and implement it in your problem.
eps0 = 8.854187817*10^-12 ;
Q0 = 3.5 ;
P0 = [1 -1 2] ;
L = 10; B = 10; H = 10 ;
m = 50 ; n = 50 ; p = 50 ;
x = linspace(-L,+L,m) ;
y = linspace(-B,+B,n) ;
z = linspace(-H,+H,p) ;
[X,Y,Z] = ndgrid(x,y,z) ;
X = X(:) ; Y = Y(:) ; Z = Z(:) ;
X0 = P0(1) ; Y0 = P0(2) ; Z0 = P0(3) ;
% GEt disatnces
R = sqrt((X0-X).^2+(Y0-Y).^2+(Z0-Z).^2) ;
Ex = Q0/(4*pi*eps0)*(X-X0)./R.^3 ;
Ey = Q0/(4*pi*eps0)*(Y-Y0)./R.^3 ;
Ez = Q0/(4*pi*eps0)*(Z-Z0)./R.^3 ;
quiver3(X,Y,Z,Ex,Ey,Ez,10)
