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Homework Help: Help calculating decibel level from intensity of sound

  1. Jan 10, 2015 #1
    1. The problem statement, all variables and given/known data

    Determine the decibel rating of the following intensities of sound.

    I = 1.0 x 10-5 W/m2

    2. Relevant equations

    The equation which relates the intensity of a sound wave to its decibel level is:

    dB = 10 * log( I / 1.0 x 10-12 W/m2)

    3. The attempt at a solution

    dB = 10 * log( 1 x 10-5 W/m2 / 1.0 x 10-12 W/m2) = ?

    I put it into my calculator and can't actually get an answer out of it. I know the answer is 70dB as I looked in the answer booklet but I couldn't get that answer by entering the equation into it?

    Any help would be greatly appreciated. Thanks
  2. jcsd
  3. Jan 10, 2015 #2

    Doug Huffman

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    Gold Member

    It's right there, 10(12 - 5)=70 by inspection.
  4. Jan 10, 2015 #3
    Thankyou. How would this one be worked out? I am very new to physics so equations are confusing at the moment:

    dB = 10 * log( 6.1 x 10-6 W/m2 / 1.0 x 10-12 W/m2) = 68 dB

    How would that be inputted into a calculator?

    Thank you very much :)
  5. Jan 10, 2015 #4

    Doug Huffman

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    Gold Member

    LOL Sorry, I haven't used a calculator in many years.

    My collection of calculators (HP-35, 41, 48) live in the same box with a half-dozen slide rules.
  6. Jan 10, 2015 #5
    No worries. Thank you for your help!
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