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Final exam wave question

  1. Jun 21, 2015 #1
    I'm a high school physics teacher and this was a question posed to my Honors Physics class.

    A light wave travels from water to air. Which of the following variables does NOT change between the mediums?"
    A. speed
    B. wavelength
    C. amplitude
    D. frequency

    I intended the answer to be frequency. But, upon further analysis, I couldn't give a good answer as to whether the amplitude changes or not. I was thinking in terms of classical waves (e.g. strings, sound, water). But, I specifically used a light wave. In perusing PF, I saw a previous thread discussing whether light as a photon has an amplitude. I'll admit the discussion got really deep, but the conclusion seemed to be that amplitude doesn't quite apply to a single photon, and for a light "wave", intensity would be a better descriptor. However, I did say amplitude.

    The students know about energy/intensity vs. amplitude, but not really about light being wave and particle. They may be familiar with the concept though. My question is whether option C was ambiguous enough to warrant accepting it as an answer.
  2. jcsd
  3. Jun 21, 2015 #2
    Wavelength and frequency are linearly related. Amplitude only depends on interference in photons, as far as I understand it.
  4. Jun 21, 2015 #3
  5. Jun 21, 2015 #4


    Staff: Mentor

    To my knowledge, C would not be a correct answer. The amplitude does change.
  6. Jun 21, 2015 #5


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    Science Advisor
    Homework Helper

    The amplitude should change as a consequence of EM boundary conditions.
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