18. Waves & Sound

Sound Intensity

Multiple Choice
A source emits a sound in the shape of a cone, as shown in the figure below. If you measure the intensity to be 100 W/m² at a distance of 0.5 m, what is the power of the source?
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Multiple Choice
A source emits sound spherically with a power of 2.2 × 10⁴ W. What is the minimum distance away from this sound that would be considered safe (a volume of 150 dB or less)?
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Multiple Choice
Suppose an explosion can just be heard over normal conversation with an intensity of $1.0 \times 10^{- 6} {W/m}^{2}$ from 10km away. At what distance from the explosion will the sound have an intensity that causes pain ( $10 {W/m}^{2}$ )? Note that this calculation ignores absorption of sound energy by air and objects.
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Multiple Choice
A speaker at a rock concert is causing you pain, so you reason the sound level must be 130dB. The speaker is 11 m away from you. To what final distance from the speaker should you move for the sound level to reach a less-painful 105 dB? Keep in mind that we are ignoring absorption of sound energy by air and objects.
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Multiple Choice
A sound wave from a police siren has an intensity of 0.01 W/m² at a certain distance. A second sound wave from an ambulance has a sound intensity level 8 dB greater than the police siren, when measured at the same distance. What is the sound intensity level (in dB) of the sound wave due to the ambulance?

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Textbook Question
(a) By what factor must the sound intensity be increased to raise the sound intensity level by 13.0 dB? (b) Explain why you don't need to know the original sound intensity
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Textbook Question
A baby's mouth is 30 cm from her father's ear and 1.50 m from her mother's ear. What is the difference between the sound intensity levels heard by the father and by the mother?
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