Ch 12: Sound Flashcards
Sound travels slowest through ______, faster through liquids, and fastest through ______.
gases
solids
p. 408
What is the relationship between frequency and the period?
Why are the percentages of the change in frequency and wavelength much greater when sound waves are used instead of radio waves in experiments?
The velocity of sound is much smaller than that of electromagnetic radiation.
When a sound source is approaching, the detected frequency will be ______.
higher
(remember higher frequency means lower wavelength)
p. 416
When a sound source is receding, the detected frequency will be ______.
lower
(remember lower frequency means higher wavelength)
p. 416
The Doppler effect is apparent whenever a sound source is moving ________ to the detector.
relative
p. 416
How is the intensity of a sound wave measured?
(what are the units and how is it defined)
W/m2
this translates to the energy transmitter per second (power) per unit area
p. 414
Mathematically, for a point source, intensity of a sound wave varies inversely as the square of the distance r from that source:
p. 414
What is the threshold of hearing?
Roughly the lowest intensity the human ear can perceive as sound at the common middle frequencies. It’s approximately equal to 10-12 W/m2. This intensity is denoted by I0.
The intensity level (or sound level) of a sound wave whose intensity is I is equal to the base-10 logarithm of the I/I0. The unit of intensity level is the bel (B). Usually we multiply this by 10 to get the intensity level, β, in decibels (dB).
Write the equation for β.
- β* = 10 log10 (I / I0)
p. 414
From the formula for intensity level in dB, what relationship can we infer?
Every time we multiply I by 10, we ADD 10 to β.
Every time we divide I by 10, we SUBTRACT 10 from β.
p. 414
If you move 10 times further away from a loud siren of constant power, what is the resultant decrease in sound level?
20 dB
p. 415
