my journey:

1. added mbar.gif graphics into folder _data/mbar.gif
so now i can compile it n it works nicely.

question:

reference:http://upload.wikimedia.org/math/5/f/f/5ff6494ee391f0ac7cfd0da8851422f3.png
can explain is this the Biot–Savart law you used to model the magnetic feild lines?  [img]http://upload.wikimedia.org/math/5/f/f/5ff6494ee391f0ac7cfd0da8851422f3.png[/img]

compare it with the code
[code]double r2,r3,f;
// caluclate magnetic field at point xp,yp use Biot-Savart Law Fproportional to dlXr/r^3
public double calFx (double xp,double yp) {
f=0;
for(int i=0;i  for(int j=0;j   r2=(xp-xc[j])*(xp-xc[j])+(yp-yc[i])*(yp-yc[i])+zc[i]*zc[i];
   r3=r2*Math.sqrt(r2);
   f-=(yc[i]*(yp-yc[i])-zc[i]*zc[i])/r3;
  }
}
return f;
}
public double calFy (double xp,double yp) {
f=0;
for(int i=0;i  for(int j=0;j   r2=(xp-xc[j])*(xp-xc[j])+(yp-yc[i])*(yp-yc[i])+zc[i]*zc[i];
   r3=r2*Math.sqrt(r2);
   f+=yc[i]*(xp-xc[j])/r3;
  }
}
return f;
}[/code]

it looks different, sorry it is difficult to follow, as Biot-Savart Law i don't have a deep understanding

i am usuallly on MSN microsoft messager : [b][color=blue]lookang[/color][/b] , can add me as frd then maybe we can arrange to discuss the applet?