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!

Difference in radius, same power and intensity?

  1. Oct 9, 2011 #1
    1. The problem statement, all variables and given/known data
    How much acoustic power propagates through a spherical surface (sound source in centre) with radius equal to 1.0m? with radius equal to 5.0m?

    I = 10^-2 W/m^2
    r = 1.0m or 5.0m
    f = 50kHz
    t = 2.0*10^-3s
    IL = 100dB

    2. Relevant equations
    I = P/4∏r^2


    3. The attempt at a solution
    i figured out that when r = 1.0, power must be 1.3*10^-1W. However, when I work out the intensity when r = 5.0, i get:

    10^-2 = P/4*∏*25
    (10^-2)(4*∏*25) = P
    3.1W = P

    However, the answer states that the power for both spheres is 0.12W... What concept am I not understanding?
     
  2. jcsd
  3. Oct 9, 2011 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    It is the same sound source which produces I = 10^-2 W/m^2 at unit distance, so its power is 0.13 W. The same power propagates through any concentric spherical surface, with less and less intensity.

    ehild
     
  4. Oct 9, 2011 #3
    ooh, i see. so basically the power stays the same because it's the same sound source (a bat, in this case), but the intensity becomes a lot less in distance. i understand now, thanks!
     
  5. Oct 9, 2011 #4

    ehild

    User Avatar
    Homework Helper
    Gold Member

    You understood it quick:smile: You are welcome.

    ehild
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Difference in radius, same power and intensity?
  1. Intensity and Power (Replies: 4)

Loading...