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Natural Science Forum / Physics / Optics / October 2005Interference - Net Curtain/Diffraction
Diffraction, seen when light passes through a diffraction grating, and the pattern produced by overlaying two net curtains (for example) are both referred to as 'interference' patterns. But it seems clear to me that these two are unrelated effects, despite the fact that they are both called Interference and can be demonstrated with similar equipment. Is there a historical background to this confusion, or am I confused and the effects are in fact related? Thanks, Scrim > Diffraction, seen when light passes through a diffraction grating, and the > pattern produced by overlaying two net curtains (for example) are both [quoted text clipped - 4 lines] > Is there a historical background to this confusion, or am I confused and the > effects are in fact related? I think that you could be mixing up two different effects: 1. Moire patterns (geometrical optics) 2. Interference patterns (physical optics) The superimposition of two periodic or almost periodic structures can give rise to a moire pattern under certain circumstances. Such as when you are looking through two curtains made with the same fabric. If the weave of the curtain is sufficiently fine and if you are observing a distant source you will also observe a diffraction pattern. This is of course a short answer, textbooks and the WWW should help you understand what's going on. On 10/29/05 4:18 AM, in article XTI8f.20217$iD.10589@fe2.news.blueyonder.co.uk, "Scrim" <none@none.com> wrote: > Diffraction, seen when light passes through a diffraction grating, and the > pattern produced by overlaying two net curtains (for example) are both [quoted text clipped - 7 lines] > > Scrim They both are examples of interference. The term arises, at least in the modern sense, from the mathematical description of the phenomena. Physically, it is associated with the fact that sinusoids of the same or nearly the same frequency can add and subtract amplitudes. This interference is sensitive to small phase differences. Any "wave" phenomenon is subject to interference. These include electromagnetic waves, acoustic wave, and probability waves. For electromagnetic waves, the effect shows up as fading in short-wave communication through x-ray diffraction with crystals, covering a frequency range of 10^12 to 1. For your screening, the frequencies are spatial rather than temporal. Moreover, interference can take place with harmonic frequencies. Bill |
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