more discussion with teacher.

teacher disagree with the simulation as it shows field lines intersecting the null point in the center.
an example is this java applet from a website instead.
http://surendranath.tripod.com/Applets/Electricity/FieldLines/EFL.html

[color=blue][b]The imperfection is resolved. Enjoy
http://surendranath.tripod.com/Applets/Electricity/FieldLines/EFL.html is actually 2 fixed points with fixed lines, may not be so ‘inquiry enabled’.[/b][/color]

i am not sure if this is correctly represented in http://surendranath.tripod.com/Applets/Electricity/FieldLines/EFL.html when
Q1 =1, Q2 = 5*Q1 for example.