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Homework Help: Properties of waves switching mediums?

  1. Feb 26, 2006 #1
    Why is it that when a wave (say transverse) passes from a dense medium (say a spring) into a less dense medium, the transmitted wave is not always larger than the original. I'm not sure, but I believe it has to do with the amount of energy in the original wave, or I'm just completely wrong.

    Also, why is it that frequency remains constant when a wave changes mediums and is this why speed changes since only wavelength changes?

    I might ask more questions later. I know a lot of this is info I could just find out from a teacher, but I'm really pressed for time this week, missed last friday, and have a test tuesday.

  2. jcsd
  3. Feb 26, 2006 #2


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    First of all, please try not to miss class. If you do, make sure someone will get class notes for you, and offer to do the same (reciprocity).

    It has to do with momentum as well as energy. At an interface, with dissimilar properties, some energy will be transmitted, and some energy will be reflected.

    Relationship between speed, frequency and wavelength in water - http://www.gcsechemistry.com/pwav5.htm
  4. Feb 26, 2006 #3

    Yes, I got class notes (I was not planning on missing class; I went home sick, and believe me - I don't like missing physics as it's the only class I can stay fully awake during:wink: ), but this situation was hazy to me and I am still slightly unclear on it. Perhaps I am not explaining my problem correctly. I am aware of how the reflection and transmissions occur in general, but I am unsure of why when a wave passes from a dense medium into a less dense medium, sometimes the transmitted wave is larger, and other times it does not get larger. What specifically causes this to happen (it being a "sometimes" situation rather than an "always" one)? In my notes it states word for word that:

    "A pulse originates in the more dense medium. As the pulse travels into the less dense medium, the speed of the transmitted pulse increases, its size increases (not always), and it's orientation...

    So I know that when dealing with dissimilar mediums, some energy is transmitted and some is reflected (which is always a given), but why is it that in this specific situation, the "not always" scenario occurs when going from more dense to less dense and what conditions must occur for this to happen. This is also confusing since no constraint such as "not always" is given to a pulse originating in a less dense medium to a more dense medium.

    Hopefully I explained it better that time. Thanks again for the help.
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