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Difficult AS Physics Question - Intensity watch

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    Almost finished a homework sheet, but got stuck on the last question:

    A student stands at a distance of 5.0m from a point source of sound, which is radiating uniformly in all directions. The intensity of the sound wave at her ear is 6.3 x 10^-6 Wm-2.

    a. The receiving area of the student's ear canal is 1.5 cm2. Calculate how much energy passes into her ear in one minute.
    b. The student moves to a point 1.8m from the source. Calculate the new intensity of the sound.


    Already figured out part a: 6.3 x 10^-6 Wm-2 x 0.15 m = 9.5 x 10^-7 Jm-1

    However, I'm not so sure about part b. I know that it will be a higher intensity since it is closer, but I'm not sure how to form the relationship between the intensity and the distance in a formula. Anyone?
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    Umm... 1.5cm2 doesnt equal 0.15m2. You have to multiply by 10^-4 instead of 10^-1 to convert to m^2 because area is a squared function of length if you know what I mean.
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    It gives you the energy per unit area for 5m from the source, you should know formula for sphere surface area. What is the total energy emitted per second?
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    For part b) remember that there is an inverse square relationship between the intensity and the distance from the source. [eg half the distance and the intensity is 4 times greater etc]
 
 
 
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