1. 14 Sound Waves character of sound waves speed of sound sound intensity resonance Homework: 2, 3, 4, 10, 17, 41, 45, 81, 91.

2. Sound Waves pressure/density waves compressions rarefactions reflects refracts (similar to light) diffracts (bends around corners)

3. Sound Spectrum ultrasonic (f > 20kHz) (human) audible (20Hz < f < 20kHz) infrasonic (f < 20Hz) dogs, cats (50Hz < f < 45kHz) bats up to 120kHz elephants as low as 5Hz

4. Sound Speed in air: v = 331 + 0.6T C m/s in solids:~ 1800 to 5000 m/s in liquids:~ 1100 to 1500 m/s in gases:~ 300 to 1200 m/s

5. Sound Intensity intensity, I: power/area [watt/m 2 ] decibel:  = 10log(I/I o ) I o =10 -12 watt/m 2. Example: 10 -9 watt/m 2 = 30 decibels

6. Example: Intensity point source of sound, 0.010 watts I at 10 meters: = power/area = 0.010watts/(4  10 2 m 2 ) = 7.96x10 -6 watt/m 2.  = 10log(7.96x10 -6 /10 -12 ) = 69dB

7. Resonance in Tubes Due to constructive interference of waves within the tube open at both ends: all harmonics closed at one end: odd harmonics only

8. Doppler Effect f’ increase on approach F’ decrease on separation Eq. 14.14a page 487

9. demos Vernier microphone, logger pro, physics with computers, voice program measure voice, chilandi plates, tuning forks, anyone with perfect pitch, meter stick? Open/closed tubes Take data on chilandi plates, compare to sand patterns with wave driver applied.

10. End

11. 11 Example of wavelength distortion due to source motion:

12. 12 Nature of Sound Waves Longitudinal Oscillations are: Condensations (higher pressure areas) and Rarefactions (lower pressure areas) Sound travels at about 343m/s at room temperature and normal atmospheric pressure

13. 13 Doppler Effect Frequency received is different than the Source frequency due to: Source Motion, Receiver Motion or, a combination of Source and Receiver motions.

14. 14 values of “A” and “f”?

15. 15 Decibels intensity level where I o = 1.0x10 -12 W/m 2. Example: Intensity of sound is 4.0x10 -5 W/m 2. Intensity level is

16. 16 Sound Intensity (I) Intensity = power/area = P/A [watt/meter 2 ] Spherical Radiation I = P/4  r 2. Example: Small speaker emits 1.0W of sound in all directions. Intensity 10m from the speaker is 1.0/(4  10 2 ) W/m 2.

17. 17 Frequency of Sound Audible Range: 20Hz to 20,000Hz Infrasonic: f < 20Hz Ultrasonic: f > 20,000Hz