What happens with the energy of a wave when there is negative interference?

Question

For example the waves leaving out of a diffration grating

But , isn´t it that energy cant be destroyed.

Answer 1

You suspect it might violate the energy conservation law, huh?
Well it doesn't, because when the waves interfere destructively somewhere, they always interfere constructively somewhere else.
It's only the repartition of energy that is changed. The total amount of energy stays the same.
In the case of a diffraction grating, one beam is split into several beams with different angles. You can be sure the sum of the energies of the beams going out is the same than that of the beam going in.

Answer 2

"Negative" energy, as you like to call it is really destructive interference. It has a cancelling effect. The sum total energy out still equals the energy in, inside your closed system..

Don't let your semantics confuse what's really happening.

Answer 3

Energy is a process as the consequence of a mass in motion. if light is a massive particle of high density then due to collision in the slots of the microcopic gratings the radiated particles of light will either separate or interfere with each other,thus difraction occurs.

Answer 4

In that case, sometimes one wave will cancel another. Their energies are opposite.

Answer 5

It decreases the energy

Answer 6

It keeps on going getting weaker and weaker but it will keep going.

Answer 7

I would have summed it up in two words " frequency dispersion"
http://en.wikipedia.org/wiki/Dispersion_(optics)