Hello there! Long time no see! I've been struggling with this thing for a long time, and finally I've been able to write something down and wonder whether it is correct or not. Unluckily, I am trying to do something that may be more difficult than it seems, so I need your help. I am going to give an attachment (.doc) in which the procedure is described. I want your opinions about the "correctness" of what I have done. It is a simple physical system, and Electromagnetism is involved. Any help will be MUCH appreciated!