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?
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)?
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.
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.
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?
Open 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
Open 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?
Open Question
For a person with normal hearing, the faintest sound that can be heard at a frequency of 400 Hz has a pressure amplitude of about 6.0 * 10-5 Pa. Calculate the (a) intensity
Open Question
You live on a busy street, but as a music lover, you want to reduce the traffic noise. (b) If, instead, you reduce the intensity by half, what change (in dB) do you make in the sound intensity level?
Open Question
You live on a busy street, but as a music lover, you want to reduce the traffic noise. (a) If you install special soundreflecting windows that reduce the sound intensity level (in dB) by 30 dB, by what fraction have you lowered the sound intensity 1in W>m2 2?
Open Question
A sound wave in air at 20°C has a frequency of 320 Hz and a displacement amplitude of 5.00 * 10-3 mm. For this sound wave calculate the (a) pressure amplitude (in Pa)
Open Question
You are trying to overhear a juicy conversation, but from your distance of 15.0 m, it sounds like only an average whisper of 20.0 dB. How close should you move to the chatterboxes for the sound level to be 60.0 dB?
Open Question
Sound is detected when a sound wave causes the tympanic membrane (the eardrum) to vibrate. Typically, the diameter of this membrane is about 8.4 mm in humans. (a) How much energy is delivered to the eardrum each second when someone whispers (20 dB) a secret in your ear?
Open Question
What is the speed of sound in air (a) on a cold winter day in Minnesota when the temperature is -25°F, and (b) on a hot summer day in Death Valley when the temperature is 125°F?
Open Question
A concert loudspeaker suspended high above the ground emits 35 W of sound power. A small microphone with a 1.0 cm² area is 50 m from the speaker.a. What is the sound intensity at the position of the microphone?