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Homework Help: MCQ Sound Wave

  1. May 29, 2010 #1
    1. The problem statement, all variables and given/known data
    Hi All,

    I have two MCQ, I could not answer them.

    All choices seem to be close to each others.

    I would be so grateful if you could help me.

    When the compression and expansion is very rapid, the sound is said to be high in:
    a) amplitude
    b) pitch
    c) frequency
    d) loudness
    e) intensity

    Pitch = Frequency so it can't be neither (C) nor (D) as I think
    Amplitude related to intensity so it can't be neither (A) nor (E)
    intensity = power/area = energy/time.area
    energy is directly propotional to the square of change in amplitude
    so it can't be (e) !!!

    Could you show me the answer with clarification please ??

    another MCQ

    If one ertr to compare the wave form of a soft sound with the wave form of a much louder sound. The loud sound will have a greater ------------
    a) frequency change
    b) intensity change
    c) pressure change
    d) energy change
    e) sound quality

    Sure, it is not (e)

    and (a), (b), (c), (d) are all interrelated !!!

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. May 29, 2010 #2

    You are getting confused here, I think

    1. If the compression and expansion are rapid, that means that the time it takes to complete a cycle of compression and expansion is small, yes?

    Now, I'm sure you understand that frequency is inversely proportional to period, so the frequency must be high.

    However, the question does not ask you the properties of the wave itself - it is asking about what the wave sounds like. If you have a high frequency, you have a high pitch. Answer *should* be (b)

    2. You are right when you say that they are related. However, everything other than intensity depends on a lot of factors other than the loudness! The only thing that can be certainly deduced from the question is that the sound will have a larger amplitude, that is to say, a larger intensity. I mean, the two sounds can both be at the same frequency, since frequency is defined not by loudness, but by the period of the wave!
  4. May 29, 2010 #3
    Thanks for your fast reply.

    2. so it's false MCQ ?!
  5. May 30, 2010 #4
    No, its just that ONLY the intensity change is related to just the difference in waveforms
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