Sign up ×   share|cite|improve this question I did some reaserch
into this and after a lot of reading I came acrose a site with a
good description of what you are talking about so here's a
link.… If you go to this site it should answer your question and
I hope it helps. –  Richard Sisson Jun 25 '12 at 20:03 this
video from MIT shows very clearly what happens to the energy
when there exists destructive interference in electromagnetic
waves. –  anna v Nov 16 '14 at 15:57 I just thought of this
question and logged on here to get an answer. Thanks for beating
me to asking it :) –  dsollen Mar 14 at 21:51  12 Answers 12  We
treated this a while back at University...    share|cite|improve
this answer up vote 19 down vote          share|cite|improve
this answer     You really would have to construct an example.
Since non-dissipative waves whose equations of motions can be
formulated by a Lagrangian will have an energy associated to
them, as you say, you'd have to find a situation/theory without
an energy quantity.