Hot chocolate effect. Tap a metal spoon inside amug of water and note the frequency fi you hear. Then add aspoonful of powder (say, chocolate mix or instant coffee) and tapagain as you stir the powder. The frequency you hear has a lowervalue fs because the tiny air bubbles released by the powderchange the water’s bulk modulus. As the bubbles reach the watersurface and disappear, the frequency gradually shifts back to itsinitial value. During the effect, the bubbles don’t appreciablychange the water’s density or volume or the sound’s wavelength. Rather, they change the value of dV/dp—that is, the differentialchange in volume due to the differential change in the pressurecaused by the sound wave in the water. If fs /fi=0.333, what is theratio (dV/dp)s/(dV/dp)i?
Hot chocolate effect. Tap a metal spoon inside a
mug of water and note the frequency fi you hear. Then add a
spoonful of powder (say, chocolate mix or instant coffee) and tap
again as you stir the powder. The frequency you hear has a lower
value fs because the tiny air bubbles released by the powder
change the water’s bulk modulus. As the bubbles reach the water
surface and disappear, the frequency gradually shifts back to its
initial value. During the effect, the bubbles don’t appreciably
change the water’s density or volume or the sound’s wavelength. Rather, they change the value of dV/dp—that is, the differential
change in volume due to the differential change in the pressure
caused by the sound wave in the water. If fs /fi=0.333, what is the
ratio (dV/dp)s/(dV/dp)i?
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