A speaker at an open-air concert emits 600 W of sound power, radiated equally in all directions.
a. What is the intensity of the sound 5.0 m from the speaker?
b. What sound intensity level would you experience there if you did not have any protection for your ears?
c. Earplugs you can buy in the drugstore have a noise reduction rating of 23 decibels. If you are wearing those earplugs but your friend Phil is not, how far from the speaker should Phil stand to experience the same loudness as you?

Respuesta :

Answer

Given,

Sound Power, P = 600 W

a) Intensity of sound,

    r = 5 m

   we know,

     [tex]I = \dfrac{P}{A}[/tex]

     [tex]I = \dfrac{P}{4\pi r^2}[/tex]

     [tex]I = \dfrac{600}{4\pi\times 5^2}[/tex]

            I = 1.91 W/m²

b) Sound intensity

  [tex]\beta = 10 log(\dfrac{I}{I_0})[/tex]

       I₀ = 10⁻¹²

  [tex]\beta = 10 log(\dfrac{1.91}{10^{-12}})[/tex]

  [tex]\beta = 123\ dB[/tex]

c) Sound experienced by the Phil

    β₁ = 123 - 23 = 100 \ dB

distance from the sound

again using sound intensity formula

  [tex]\beta = 10 log(\dfrac{I}{I_0})[/tex]

  [tex]100= 10 log(\dfrac{I}{10^{-12}})[/tex]

  [tex]I = 10^{-12}\times 10^{10}[/tex]

where, I = P/A

  [tex]\dfrac{P}{4\pi r^2} = 10^{-2}[/tex]

  [tex] r^2 = \dfrac{600}{0.04\times \pi}[/tex]

        r = 69.09 m

Distance where Phil will experience same sound intensity without earplug is equal to r = 69.09 m