4) An audio speaker producing a steady sound at an outdoor concert is 40 ft away from you. If you move to a position where the speaker is 72 ft distant, by what factor will the amplitude of the sound change?

A_{f /} A_{i =}

13) Approximately how many times louder is a 170-dB sound than a 90-dB sound?

17) What is the speed of sound (in m/s) in helium at the normal boiling temperature of water?

_____m/s

18) A 710-Hz sound travels through pure carbon dioxide. The wavelength of the sound is measured to be 0.38 m. What is the speed of sound in carbon dioxide?

______m/s

19) What frequency of sound traveling in air at 20C has a wavelength equal to 1.6 m, the average height of a person? _____Hz

'

20) Ultrasound probes can resolve structural details with sizes approximately equal to the wavelength of the ultrasound waves themselves. What is the size of the smallest feature observable in human tissue when examined with 11-MHz ultrasound? The speed of sound in human tissue is 1,540 m/s.

________m

21) A sound pulse emitted underwater reflects off a school of fish and is detected at the same place 0.12 s later (see the figure below). How far away are the fish?

_______m

22) The sound level measured in a room by a person watching a movie on a home theater system varies from 50 dB during a quiet part to 70 dB during a loud part. Approximately how many times louder is the latter sound?

________m