Sound Waves with Clicker Questions

1. Sound Waves
Edie Ye

2. Sound Waves
 A sound wave is a longitudinal wave and a type of
mechanical wave
 A sound wave travels through compressions and
rarefactions

3. Connection to sound wave
 A sound wave behaves similar to other waves, so think
about this: comparing the amplitudes of two sound waves,
which sound wave would we expect to be louder, the one
with a lower amplitude or the one with a higher amplitude?
Now think about frequency, does it change with an increase
in amplitude?
 It would be louder at the higher amplitude and the frequency
would not change. The frequency doesn’t change because
think about this: when you increase the volume of your iPod
when you are listening to music, it happens seamlessly.
Increasing the amplitude means increasing the sound and if
the frequency had changed, wouldn’t there have been an
interruption?

4. Clicker 1
 Consider the diagram below. Where is pressure the
highest? Where pressure is the highest, would the
displacement be positive, at zero, or negative?

5. Clicker 1
 a. at compression; positive
 b. at compression; negative
 c. at compression; zero
 d. at rarefaction; positive
 e. at rarefaction; zero

6. Clicker 1 Explained
 From the diagram, we can see that pressure is highest
at compression. We can’t see the displacement
however, but because we know for an area’s pressure
to be high, both sides (i.e. left and right) must have
particles pushed towards that area to create that high
pressure and hence a balance which results with zero
displacement. This is similar to velocity and
displacement, where the displacement is at zero, the
velocity is at its maximum. This is because both
velocity vs. displacement, and pressure vs.
displacement are out of phase by π/2 rad.

7. Clicker 2
 Consider the diagram below. Where is pressure the
lowest? Where pressure is the lowest, would the
displacement be positive, at zero, or negative?

8. Clicker 2
 a. at compression; positive
 b. at compression; negative
 c. at compression; zero
 d. at rarefaction; positive
 e. at rarefaction; zero

9. Clicker 2 Explained
 From the diagram, we can see that pressure is lowest
at compression. We can’t see the displacement
however, but similar to high pressure, it is at zero.

10. What is speed dependent on?
 Dependent on the fraction of volume change when we
change pressure which is known as bulk modulus, B
 Equation for bulk modulus: B= -VΔp/ΔV, where ΔV is
change in volume fraction and Δp is change in pressure
 Dependent on the density of the material
 Equation for speed of sound: v=√(B/p), where B is bulk
modulus and p is density

11. Clicker 3
 The speed of a sound wave is dependent on
wavelength.
a. true
b. false

12. Clicker 3 Explained
 The speed of sound is is dependent on the equation:
v=√(B/p) so it is independent from wavelength.

13. Clicker 4
 Say the bulk modulus of unknown substance one
(solid) is 4 x 107 and its density is 15 000. Say the bulk
modulus of unknown substance two (liquid) is 4 x 105
and its density is 1 000. We can expect the velocity of
unknown one to have a higher velocity than that of
unknown two.
 a. true
 b. false

14. Clicker 4 Explained
 Although the effect of density decreases the speed of
the sound, the increase in bulk modulus from gas to
liquid to solid is greater than the density increase (in
terms of ratio) and hence the trend is that the speed of
sound in solids is usually (e.g. solid) greater than the
speed of liquid (e.g. liquid).
 Calculation of unknown one: √[(4.0 x 107)/15 000] = 52
m/s
 Calculation of unknown two: √[(4.0 x 105)/1 000] = 20
m/s

15. Clicker 5
 You are in a 50 meter swimming pool and there is a kid
swimming about 30 meters inside the water away from
their parent who is is yelling at the him to get out of the
water (This happens occasionally at the pool and angry
parents are very loud). The lifeguard is standing 25
away from the parent and you are standing 5 meters
away from the parent. Who do we expect to hear the
parent first? second? third?

16. Clicker 5
 a. all at the same time
 b. you ;lifeguard; kid
 c. you and lifeguard at same time; kid
 d. lifeguard and kid at same time; you
 e. you; kid; lifeguard

17. Clicker 5 Explained
 We can expect you to hear the sound first because
sound in water travels just over 4 times than that of air
but because you are less than 4 times away you can
hear the parent first. We can expect the kid to hear the
sound second because although the kid is further away
from the parent than the lifeguard, we expect the speed
of sound to travel faster (just over 4 times) than that of
air. We, then, can say the lifeguard hears it last.

18. Thank you for watching

19. Work Cited
Hawkes, Robert, Javed Iqbal, Firas Mansour,
Marina-Bolotin, and Peter Williams. Physics for
Scientists and Engineers. Vol. 1. : Nelson, n.d.
Print.