Hello there, I am glad that I found this forum. Because I have a little bit trouble with theoretical physics. :yuck: The problem is the Green function in theoretical electrodynamic. I try to understand the difference between the Dirichlet Condition and the Neumann Condition. I understand the mathematic behind this theory, but If possible I would like to picture this stuff for better understanding. Dirichlet Condition shows a picture with a mirror charge, a real charge and the zero potential between it. So it means G(r,r')=0 and r' is on the surface. Neumann Condition means dG(r,r')/ dn'= 4pi/F with r' on the surface and F is the whole surface. Now I can't understand what's the meaning of Neumann condition - not mathematicly but as a picture . Maybe I misunderstood this theory completely. I hope somebody knows what I mean and can help me. thanks a lot the lost boy "Mathematics? What is it ? Can I eat it ?"