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Phase Difference of Waves
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by angel_of_stone
on 2009-12-04 06:33:17
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I'm taking an optics course and the prof keeps talking about the phase difference of 2 waves. I understand the concept, in phase is constructive interference and out of phase is destructive, but what I don't understand is how the phase of each wave is calculated. My prof. isn't very good, and the book has almost no information on wave phase at all. Can anybody help me?
"But as Deepak Chopra taught us, quantum physics means that anything can happen at anytime and for no reason." -Prof. Hubert J. Farnsworth
"I don't have any opinions anymore. All I know is that no one is better than anyone else, and everyone is the best at everything." -Seymour Skinner "...if I got trapped by an evil wizard then I did enough cool s**t in my life to be content with it ending. " -Wolf |
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Re: Phase Difference of Waves
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by
on 2009-12-04 06:40:24 (edited 2009-12-04 06:40:43)
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Real-life waves are often calculated by counting wave peaks. Say an ocean wave sloshes up on the beach. The moment it begins to recede I click my stopwatch. After several waves, a patten emerges. Each wave comes a few seconds after the previous one. Similarly, you can use a pressure sensor to count waves by recording the time the pressure is maximum. Or you can measure your rubber ducky as it bobs up and down in the bathtub. Purely theoretical waves can be described by equations. Say you have 2 equations: Y = sin(X) and Y = sin(X + π) They are out of phase by the value &pi. You can graph them to see how they compare. If for a given X value, one wave peaks where the other wave is at it's lowest, they are destructively interfering by virtue of being out of phase. If the two graphs overlap, they're constructively interfering and in phase. Does that help? 
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Re: Phase Difference of Waves
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by angel_of_stone
on 2009-12-04 06:49:04
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Yeah, thanks.
"But as Deepak Chopra taught us, quantum physics means that anything can happen at anytime and for no reason." -Prof. Hubert J. Farnsworth
"I don't have any opinions anymore. All I know is that no one is better than anyone else, and everyone is the best at everything." -Seymour Skinner "...if I got trapped by an evil wizard then I did enough cool s**t in my life to be content with it ending. " -Wolf |
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Re: Phase Difference of Waves
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by SuicidopoliS
on 2009-12-06 15:37:23 (edited 2009-12-06 15:37:50)
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I would just like to add, as a reaction to the "what I don't understand is how the phase of each wave is calculated" statement of the OP, that the phase of a wave is something you normally don't have to calculate. It should be given to you, for the simple reason that there isn't much to calculate anyway. The phase of a wave only has meaning when you compare it to some reference. So, a statement like for example "wave B is 25° out of phase" is meaningless, but it becomes meaningful once you add "compared to wave A." In that case, as Gendou pointed out (and using the same Y = sin(X) equation), this would mean that when wave A is reaching a Y value that equals sin(X), wave B would be reaching a Y value that equals sin(X-25°). Also, talking about the phase of waves is only meaningful when talking about waves that are oscillating at the same frequency. I hope i didn't make things more confusing, instead of clarifying them... In case i failed, blame the beer! Mmm... beer is gooood... .oO° Life's THE CURE, the rest are details! °Oo. |