1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Sound waves and amplitudes Problem

  1. Sep 14, 2014 #1
    1. If there is a sound wave travelling in the air, will the amount of air transported by the wave be proportional to the intensity of the wave?
    Here is my answer: yes, because as the energy of the wave is related to the square of the amplitude of oscillations, the more energy you have, the more the wave will be able to travel further and the more amount of air will be affected. My teacher said this is wrong and gave me 0. Why?

    2. Is the amplitude independent of the wavelength and frequency?
    Here is my answer: yes, the wave speed in the medium determines wavelenght and frequency, but amplitude is separate. I got half points for this one.

    What is wrong here?
  2. jcsd
  3. Sep 14, 2014 #2
    I can't answer your first one because I haven't done sound stuff in a long time, however, for question two:

    Correct: Yes
    Incorrect: The wave speed in medium

    Amplitude is a measure of how big the wave is. Wave length is the distance between crest-crest or trough-trough and frequency tells us how many waves are passing a point per second. Bringing in medium and wave speed is kind of unrelated to the question so it in a way shows you don't really know what you are talking about.

    You can think of it like this.
    If you look at a sine graph. The amplitude is 1. (The highest it can be is 1, and lowest is -1)
    However if I change the distance between the waves, the amplitude still stays as 1. This is because frequency and wavelength, doesn't change the "size" of the wave, they affect the distance between two points on a wave.

    Hopefully I explained that well enough.
  4. Sep 14, 2014 #3


    User Avatar
    Science Advisor

    In a linear acoustic wave in air, the air moves back and forth so there's no net transport (of mass) at all.

    The air transported during each back-and-forth motion is affected by the pressure and the velocity in a more complicated way, but I don't think this is what the question is asking.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted