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Physics
Classical Physics
Optics
Why do waves diffract, really?
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[QUOTE="Drakkith, post: 6030072, member: 272035"] I think the key idea of diffraction is that the wavefront can't be discontinuous. That is, it can't contain gaps or instantaneous jumps in its amplitude between two adjacent points. Imagine a small column of water with completely straight, vertical sides, that is traveling through the water. These perfectly straight sides represent discontinuities in the wavefront since the amplitude of the wave goes from maximum to zero instantly. This can't physically happen, as gravity would pull down on the column and the discontinuity would be destroyed as the column turns into a proper wave. This, of course, is exactly what happens in diffraction, except that that such a discontinuity never existed in the first place. Instead, large, quick changes in the amplitude of the wave end up being smoothed out as the wave travels. So when a wave passes by a barrier or through an aperture, the wavefront [I]must[/I] diffract in order to avoid discontinuities. An analogous effect occurs in other types of waves. EM waves cannot have instantaneous jumps in their field vectors (the things that represent the strength and direction of the force of the EM field) and so also undergo diffraction. Sound waves cannot experience discontinuities in their pressure. The pressure from the air in one part of the wavefront pushes on adjacent areas, preventing any discontinuity and causing diffraction as the wave travels. Nothing magical about it. Look at a sound wave. The pressure from the air in one part of the wavefront pushes on the surrounding areas, and in turn they are pushing on adjacent areas too. We can model this as the wavefront being made up of an infinite amount of points, with each point generating its own spherical wave that all interact to form the single, large wavefront that is observed. [/QUOTE]
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Classical Physics
Optics
Why do waves diffract, really?
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