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# Physics - Sound Intensity

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A ten-year exposure to the sound of a riveting machine will cause your threshhold of hearing to shift from 0 dB to 30 dB. What is the sound intensity corresponding to 30 dB? The normal lowest detectable intensity is 1.0 X 10 -12 W/m squared.

https://brainmass.com/physics/intensity/physics-sound-intensity-247152

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## Physics: Sonar and Frequency

1. A sonar signal from a "fish finder" in fresh water returns 0.0460 seconds after being transmitted. What is the distance to the fish that reflected the sound?

2. (a) What frequency is received by a person watching an oncoming ambulance moving at 110 km/h and emitting a steady 800 Hz sound from its siren? The speed of sound on this day is 345 m/s. (b) What frequency does she receive after the ambulance has passed?

3. A TV is producing sound at an intensity of 5.0 x 10^(-5) W/m^2, measured at a distance 8.0 feet from the speaker. (A) What is the sound level in dB? (B) Assuming the inverse square law holds for this situation, what is the sound level in dB at a point 24 feet from the TV?

4. The ear responds to intensities which can vary over a factor of 10^(12). Suppose you built an instrument which could measure distances which vary by this same range. The smallest distance the instrument could measure is 1 mm. What would be the largest distance it could measure? Give an example of a physical situation involving this distance (e.g. the width of a continent, the earth-sun distance, or some example like that.)

5. If your roommate turns up the radio, increasing the sound level from 70 dB to 76 dB, what is the factor by which the intensity (in W/m^2) increases?

6. A mandolin is tuned like a violin, but has two strings for each note. Suppose one of the top ("E") strings vibrates at 660 Hz. When both strings are played together, you hear beats at a frequency of 3.0 Hz. What are the possible frequencies at which the other "E" string is vibrating?

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