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# Wave interference

Waves add and subtract their amplitudes when they overlap, a phenomenon known as wave interference. Learn how overlapping waves can lead to constructive interference, forming amplified waves, or destructive interference, resulting in cancelled waves. Uncover the significance of phase shifts and path length differences in shaping wave behavior. Created by David SantoPietro.

## Want to join the conversation?

• Is this really possible? Can someone make a video with like actual speakers...? Its really hard to believe.. esp the part where he says u just need to move the second speaker 1/2 the wavelength..
• Yes, this really happens. We looked at examples in physics class and when wavelengths are 180 degrees out of phase or shifted one half wavelength, then you will hear nothing. Physics is crazy.
• If destructive interference takes place between two light waves, what happens to the photons which were there in that light?
• The photons are not destroyed. In the areas where there is destructive interference, the photons have a lower probability of being in that region.
• when destructive interference happens,where does the energy contained by the wave go.like,it can't just cancel out and become nothing,right?
• What a fantastic question !

In single slit diffraction, as an example, the energy from the 'dark, minimum' regions will be found n the 'brighter, maxima,'

Hope that helps

:-)
• What if the phase difference was not pi or multiples of it ? i.e 28.7
• Then you would get partial interference rather than complete interference.
• At , we say that you won't be able to hear anything, however, you could still hear something at the time when the waves weren't cancelling each other, right? So, the first 1/2 wave?
• Yes. Since the waves are not cancelling each other, there will be sound.
Hope this helps... :)
• what is the expression for focal length of a lens/mirror in a medium other than air?
• The expression is still the same because there is no difference. The change in direction of a light beam occurs in the glass of the lens or mirror, otherwise it is simply travelling in a straight line where the medium does not matter.
(1 vote)
• Does destructive interference also work with light? Why have I never seen that happen?
(1 vote)
• Yes, it does. The thing about observing destructive interference is that you need to do it in a controlled way. Light emitted by the sun or by regular lamps is too chaotic to actually produce a point where all waves destroy themselves. When we do experiments, we always use lasers, because they provide us with an organized beam, where all the waves are parallel and in phase with each other. Sunlight, on the other hand, comes in very different phases, thus the intensity just becomes an uniform statistical average from the interference of all those phases.
• why does the existence of cut off frequency favour a particle theory for light rather than a wave theory?