1. Frequency Period Wavelength
Two strings, one thick and the other thin, are connected to form one long string. A wave travels along the string and passes the point where the two strings are connected. Which of the following changes at that point:
Frequency
Period
Wavelength

2. Sound waves
Longitudinal
Speed of sound

3. Sound waves Velocity of sound in air at 20o is 343 m/s
Helium is lighter than air
Velocity of sound in helium at 20o is 972 m/s

4. The velocity of sound in air The velocity of sound in liquid
Sound tend to travel faster in liquids and solids (the molecules are closer together).
The velocity of sound in air
vin air = 343 m/s
The velocity of sound in liquid
vin water = 1490 m/s
The velocity of sound in a solid
vin Aluminum = 5100m/s
Cool experiment – make a milkshake!

5. Without molecules we cannot have a pressure wave
Why do we not hear collisions and explosions from outer space?
In a vacuum there are not any molecules
Without molecules we cannot have a pressure wave
Sound cannot travel through a vacuum.
Sound in a vacuum Demo

6. JOHN 14:27
Peace I leave with you, my peace I give to you: not as the world gives, give I to you. Let not your heart be troubled, neither let it be afraid.

7. Intensity of sound
Intensity depends on __________ and the _____________ from the source.
Power
Distance

8. Spherical Waves / Plane Waves

9. Decibel Scale
Zero decibels refers to the threshold of hearing

10. log (10x) = x log 10 = x
10logx=x

11. log(ab)=log a + log b
log(a/b)=log a - log b

12. Decibel Scale
Zero decibels refers to the threshold of hearing

13. At a rock concert a meter placed at 2 m in front of a loudspeaker measures 130 dB. What is the power output of the speaker?

14. At a rock concert a meter placed at 2 m in front of a loudspeaker measures 130 dB. How far away do I need to stand to be at a safer level of 90 dB?

16. If you increase the intensity by a factor of 1000, add ____ to the decibel level.
3 dB
10 dB
20 dB
30 dB
60 dB

17. If you increase the intensity by a factor of 2, add ____ to the decibel level.
3 dB
10 dB
20 dB
30 dB
60 dB

18. Can you detect a 3dB difference (50% loss)

19. Other Decibel Scales
Weighting
dBm
dBV
dB SPL
dBFV

20. Consider music from a radio. If I turn up the volume
so that the sound level is 20 dB louder, by what factor
has the intensity increased?
(a) 10
(b) 20
(c) 100
Q15-2

21. When I sit one meter from a radio, the sound level is
80 dB. How far from the radio should I sit to reduce
the sound level to 60 dB?
(a) 3 m
(b) 10 m
(c) 30 m
(d) 100 m
(e) 300 m
Q15-3