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Unformatted text preview: Question 1 Two 1D waves of amplitude A and period T and constant phase φ are superposed. If wave 1 travels 13.5 wavelengths further than wave 2, will the interference be constructive, destructive or partial? When you answer quiz questions, we look very critically at your answers. So it is only fair that our questions come under the same scrutiny. The ques tion says that wave 1 travels 13.5 wavelengths further than wave 2. Further until what? It just stops travelling? It becomes a 2D wave instead? Of course we know what is being asked, I just want to point out that clarity is important and we will pick you up on it (so we should apologise when we do it ourselves!). It means that we have picked a particular point, and we are interested in the interference at that particular point. Wave 1 travels 13.5 wavelengths further than wave 2 to get to that point. What type of interference is at that point? The quick answer is that everything about these waves is the same except the path length difference. The path length differs by 13.5 wavelengths. Shifting it over 13.5 wavelengths leads to completely destructive interference. A slightly longer answer is that the path difference is 13.5 wavelengths. This corresponds to a total phase difference of ΔΦ = 2 π λ ( x 1 x 2 ) = 2 π λ ([ x 2 + 13 . 5 λ ] x 2 ) = 2 π λ (13 . 5 λ ) = 27 π. As an odd multiple of π , we know that the interference is destructive. 1 Question 2 Two 1D waves of amplitude A and period T are superposed. The difference between their fixed phase constants is 1/2 a cycle ( π or 180 ◦ ). If wave 1 travels 37 wavelengths further than wave 2 to a)....
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 Spring '09
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 Physics, Wavelength, total, Total Phase

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