What is destroyed when destructive interference occurs

From my answer here- PSE-anti-laser-how-sure-we-are-that-energy-is-transported. The Poyinting vectors, and the momenta vectors as the E, B fields are symetric. When we do 'field shaping' with antenae aggregates we simply use Maxwell eqs and go with waves everytime. When we got near a null in energy in some region of space we dont get infrared radiation to 'consume' the canceled field. Antenae in sattelites vaccum work the same way as the ones at Earth surface to shape the intensity of the field.

Because the "Poyinting vectors" add to null there is no doubt, imo, that energy vanish. See the antilaser experiment.

We dont have theory? Then we must rethink. IMO energy is not transported. What is propagating is only an excitation of the medium we call it photons and energy is already 'in site' vacuum, or whatever name we call the medium. Maxwell's description of the energy of the light wave is of an undulating energy that predictably reaches a maximum and later becomes zero.

The proposed solution to this problem is to calculate the mean of the energy when the fields are maxima. What is the physical meaning of an energy that have to be averaged in order to have the real magnitude. If the principle of conservation of energy is to be applied to this phenomenon, the energy must be constant, have an unique value for each instant during the movement of the wave. What is the meaning of that situation that has not been recognized for more than a century?

What almost nobody want to admit is that electromagnetism is incomplete, because cannot describe the electromagnetic radiation adequately, and generate a violation of the principle of conservation of energy.

NO Then we must rethink. But this is only an idea, an intuition, without support or evidence. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. What happens to the energy when waves perfectly cancel each other? Ask Question. Asked 9 years, 7 months ago. Active 11 months ago. Viewed 81k times. Improve this question. Add a comment. Active Oldest Votes.

Improve this answer. Terry Bollinger Terry Bollinger It is well established that in this scenario, there is minimum reflection and maximum transmission through the ARC. So destructive interference does not carry energy. Quantum mechanically, the EM wave is the wave function for photons. Photons actually carry energy. Is it appropriate to compare destructive interference in mechanical waves and EM waves? Just quantized. Work causes displacement along a vector. If wave A causes exactly opposite displacement to wave B, the waves will fully cancel they do not form a standing wave!

This is not because energy has been lost. Its because you have combined negative and positive energy to create zero energy. Equilibriums do not violate the laws of physics Be careful no not to confuse convenient mathematical abstractions with the actual flows of energy in the physical world, which for classical physics are always positive. Show 3 more comments. The thing is, if multiple waves globally cancel out, there are actually only two possible explanations: One or more of the sources is actually a drain and converts wave energy into another form of energy, e.

For example, plane waves physically don't exist But when used in the Fourier Transform they are still very useful because their total energy is infinite. Community Bot 1. Tobias Kienzler Tobias Kienzler 6, 2 2 gold badges 36 36 silver badges 57 57 bronze badges. You can have two wavepackets shifted in phase by pi, and you guide the two wave packets into the same region so that they cancel. In this case, both waves have an upward displacement; consequently, the medium has an upward displacement that is greater than the displacement of the two interfering pulses.

Constructive interference is observed at any location where the two interfering waves are displaced upward. But it is also observed when both interfering waves are displaced downward. This is shown in the diagram below for two downward displaced pulses. In this case, a sine pulse with a maximum displacement of -1 unit negative means a downward displacement interferes with a sine pulse with a maximum displacement of -1 unit.

These two pulses are drawn in red and blue. The resulting shape of the medium is a sine pulse with a maximum displacement of -2 units. Destructive interference is a type of interference that occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction.

This is depicted in the diagram below. In the diagram above, the interfering pulses have the same maximum displacement but in opposite directions. The result is that the two pulses completely destroy each other when they are completely overlapped.

At the instant of complete overlap, there is no resulting displacement of the particles of the medium. This "destruction" is not a permanent condition. In fact, to say that the two waves destroy each other can be partially misleading.

When it is said that the two pulses destroy each other , what is meant is that when overlapped, the effect of one of the pulses on the displacement of a given particle of the medium is destroyed or canceled by the effect of the other pulse. Recall from Lesson 1 that waves transport energy through a medium by means of each individual particle pulling upon its nearest neighbor. When two pulses with opposite displacements i. Once the two pulses pass through each other, there is still an upward displaced pulse and a downward displaced pulse heading in the same direction that they were heading before the interference.

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Skip to content. Mathematical Methods for Optics. Robert E. Wave interference: where does the energy go? Posted on April 7, by skullsinthestars. The situation in question is as follows: suppose you have a harmonic wave on a string traveling to the right such that in a snapshot of time, the string looks as follows: This wave carries energy , and there is a net flow of energy to the right.

The sum of the two waves then vanishes: The two waves cancel each other out, leaving a completely unmoving string due to destructive interference. The second wave is generated locally at a point on the string by some sort of applied force: Individually, the first wave is propagating entirely to the right; the second wave spreads out in both directions from the point of application.

We have: There is complete destructive interference to the right of the second excitation. The disc is read by focusing light onto the surface, and measuring the amount of light reflected back, as crudely illustrated below: Light from a laser passes through a beam splitter and is focused by a lens onto the disc.

It gets diffracted into a direction where the lens cannot detect it color coded for clarity : To summarize, these are the two thoughts I had when the student asked me his question: 1 one needs to consider all sources of waves when trying to interpret wave interference phenomena, and 2 in general, wave interference results in a change in where light goes.

For instance, let us return to our waves on a string, and consider interference between waves generated by two local excitations: What do we make of this situation? Share this: Tweet. Like this: Like Loading This entry was posted in Optics , Physics. Bookmark the permalink.

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David says:. December 13, at am. Micah says:. December 15, at am. December 17, at pm. Joao Rodrigues says:. August 22, at am. Thanks in advance. The front of that speaker moved this far. So how far was that? Let me get rid of this. That was one wavelength. So look at this picture. From peak to peak is exactly one wavelength. We're assuming these waves have the same wavelength.

So notice that essentially what we did, we made it so that the wave from wave source two doesn't have to travel as far to whatever's detecting the sound. Maybe there's an ear here, or some sort of scientific detector detecting the sound.

Wave source two is now only traveling this far to get to the detector, whereas wave source one is traveling this far. In other words, we made it so that wave source one has to travel one wavelength further than wave source two does, and that makes it so that they're in phase and you get constructive interference again.

But that's not the only option, we can keep moving wave source two forward. We move it all the way to here, we moved it another wavelength forward. We again get constructive interference, and at this point, wave source one is having to make its wave travel two wavelengths further than wave source two does. And you could probably see the pattern. No matter how many wavelengths we move it forward, as long as it's an integer number of wavelengths we again get constructive interference.

So something that turns out to be useful is a formula that tells us alright, how much path length difference should there be? So if I'm gonna call this X two, the distance that the wave from wave source two has to travel to get to whatever's detecting that wave.

And the distance X one, that wave source one has to travel to get to that detector. So we could write down a formula that relates the difference in path length, I'll call that delta X, which is gonna be the distance that wave one has to travel minus the distance that wave two has to travel.

And given what we saw up here, if this path length difference is ever equal to an integer number of wavelengths, so if it was zero that was when they were right next to each other, you got constructive.

When this difference is equal to one wavelength, we also got constructive. When it was two wavelengths, we got constructive. It turns out any integer wavelength gives us constructive. So how would we get destructive interference then? Well let's continue with this wave source that originally started in phase, right? So these two wave sources are starting in phase.

How far do I have to move it to get destructive? Well let's just see. I have to move it 'til it's right about here. So how far did the front of that speaker move? I can keep moving it forward.

Let's just see, that's constructive. My next destructive happens here which was an extra this far. How far was that? Let's just see. So let's just keep going.

Move wave source two, that's constructive. We get another destructive here which is an extra this far forward, and that's equal to one more wavelength. So if we get rid of this you could see valley to valley is a whole nother wavelength. So this is how the path length differences between two wave sources can determine whether you're gonna get constructive or destructive interference.

But notice we started with two wave sources that were in phase. These started in phase. So this whole analysis down here assumes that the two sources started in phase with each other, i. What would this analysis give you if we started with one that was Pi shifted?