If I have a long coaxial wire with open end and apply a short voltage pulse, that pulse begins propagating through it until it reaches the end. Then, it reflects back to where it came from. I understand that it behaves like a normal wave, maintaining its energy and bouncing when it reaches a wall. What I don't understand is that the measured voltage at the end of the wire is DOUBLE the applied voltage. http://www.aps.anl.gov/Science/Publications/lsnotes/ls156/Images/ls156_f1.gif In books, I read that the voltage at the end of the wire is always the sum of the incident and the reflected one, like: V=Vi+Vr But they never explain where does that formula come from. Does anyone know WHY is it the sum of the other two? Edit: Should I ask this in general forum?