When a charged particle moves in an electric field between two electrodes, say in a detector, the current due to the charged particle doesn't suddenly appear when it gets to the electrode, but a current is induced in both electrodes proportional to the distance traveled through the electric field by the charged particle. (If the electric field is not uniform that needs to be taken into account.)
This effect was described by one of the old vacuum tube scientists in a bygone era and is called after his name--the "whatsit" theorem. I am looking for his name and the name of his theorem. This is something I used to use in a previous life and after all these years I can't recall it.
Any ideas?