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Homework Help: Need help to find intensity of waves.

  1. Feb 14, 2012 #1
    1. The problem statement, all variables and given/known data

    A tiny vibrating source sends waves uniformly in all directions. An area of 3.25 cm2 on a
    sphere of radius 2.50 m centered on the source receives energy at a rate of 4.20 J/s.

    (a) What is the intensity of the waves at 2.50 m from the source and at 10.0 m from the

    (b) At what rate is energy leaving the vibrating source of the waves?

    2. The attempt at a solution

    I attemped the first part of the question using this equation :

    I = P / A
    A = 4 Pi r^2

    so I = 4.2 / 4 * Pi * (2.5)^2 = 0.053

    I asked my supervisor and he told me that my answer is wrong.

    Any one who knows how i can go through this question ?
    Thanks in advance
  2. jcsd
  3. Feb 14, 2012 #2
    The power of 4.2J/s is passing through an area of 3.25cm2....not the surface area of the sphere.
    I think you should also give intensity as W/m^2 so you will need to convert units to do that.
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