1. Not finding help here? Sign up for a free 30min 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!

Finding sound level intensity

  1. Mar 13, 2008 #1
    1. The problem statement, all variables and given/known data
    A person standing a certain distance from an airplane with four equally noisy jet engines is feeling a sound level intensity bordering on pain, 114 dB. What sound level intensity would this person experience if the captain shut down all but one engine?



    I have no idea how to do this problem. I thought this was relative intensity so i plugged it into the formula and found intensity. Now i'm not sure what to do. Thanks!
     
  2. jcsd
  3. Mar 13, 2008 #2

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It is a relative intensity problem. Which formula did you use? You were supposed to enter that into Part 2 of the posting template.

    Show us what you did. That was supposed to go into Part 3 of the posting template.
     
  4. Mar 13, 2008 #3
    Yeah, i was in a rush when i posted that because my computer's being repaired and i'm at the library and time was running out. Here's my work

    I used relative intensity=10log (I/Io)

    114=10log(I/1e-12) and got 0.251 w/m2 for I. I do not know what to do after this.
     
  5. Mar 13, 2008 #4
    OK, you have the value for I, divide by four and calculate the new sound level intensity.
     
  6. Mar 13, 2008 #5
    Is it 108 Hz?
     
  7. Mar 13, 2008 #6
    i just submitted and it was correct. THanks for your help :)
     
  8. Mar 13, 2008 #7
    No problem.

    The thing to realise is, you had the value for the power / m^2 at whatever arbitrary distance from the plane, then 3/4 of the engines were shut down, so you automatically know the new power / m^2 at this arbitrary distance.
     
  9. Jul 1, 2009 #8
    I have the same problem. Except instead of 114 dB it's 121 dB. I do not understand where the 1e-12 came from. Can someone tell me please?

    Also, here is what I have done so far:

    121=10log(I/Io)
    121/10=log(I/Io)
    10^12.1=I/Io

    Now I do not know what to do... I am stuck there since I have no clue to what Io is and we're trying to solve for I- two variables one equation...

    Please Help.
     
  10. Jul 1, 2009 #9

    LowlyPion

    User Avatar
    Homework Helper

    Io = 10-12 w/m2

    This is the lowest threshold of human hearing.

    So the ratio of the sound intensity to that is 121/10 or

    I = 121dB can also be written as 1012.1*10-12 w/m2
     
  11. Jul 1, 2009 #10
    I did that and I got an answer of .315 dB
    I need the answer to be in dB to submit. Can you tell me what I am doing wrong here?
     
  12. Jul 1, 2009 #11

    LowlyPion

    User Avatar
    Homework Helper

    Perhaps you should show your work. And maybe even what the problem is, because, if it is the same as the OP here where 3 jet engines cut out, you won't be getting .315 dB, if you calculated it correctly.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Finding sound level intensity
  1. Sound intensity level (Replies: 10)

Loading...