1. Reflection, transmission of sound
The bigger change in acoustic impedance z of sound between the two materials, the more sound is reflected.

2. Why do we use ultrasound instead of normal sound for this?

4. Energy in sound
Intensity and power

5. Energy in sound
Intensity vs distance (spherical emission)

6. A spherical speaker puts out an intensity of 10 W/m2 at a distance of 1.5 meters. P1. The intensity at 3 meters away is _________W/m2 A: 1.0 B: 2.5 C: 3.3 D: 5.0 E: 10 The total power the speaker puts out is _______ W.

7. Decibel intensity scale
We hear over a huge range of intensities
So use logarithmic scale (powers of 10)

8. Gun blast (arm’s length) With pain 100 140
Damage
W/m2 dB
Jet engine at 1 ft
Instant
106
180
Gun blast (arm’s length)
With pain
100
140
Rock concert (best seats)
If 10 min/day 1­
120
Power mower
at 3 ft.
If all day
10-2
Vacuum cleaner, 3 ft.
10-4 80
Conversation, 3 ft.
10-6 60
Whisper
10-9 30
Softest sound heard
10-12

9. Intensity depends on distance from source!
OSHA regulations:
No more than 90 dB averaged over 8 hour day.

10. Properties of logs
“Log(x) is the power you raise 10 to, to get x.” or x= 10log(x) log(100) = log(106) = log(ab) = log(a) + log(b) If log(3) = 0.477, log(300) = log(3) + log(100)=

11. Properties of logs
Compare two intensities: If you increase I by a factor of X, add ___________ dB If you increase I by a factor of 10, add ___________ dB If you increase I by a factor of 100, add ___________ dB If you increase I by a factor of 1000, add ___________ dB If you increase I by a factor of 2, add ___________ dB [log (2) = 0.301]

12. P2. If you increase intensity I by a factor of 8, add ___________ to the decibel level (Hint: do it with 2’s) A: 6 B: 8 C: 9 D: 12 E: 80

13. Doppler Shift—“Race Car Effect”
Applications Doppler ultrasound: blood flow imaging in heart Radar and laser speed tests

14. Doppler effect
Frequency observed _______________when the source and observer approach each other, and ______________when they go away from each other.
stokes.byu.edu/teaching_resources/doppler_flash.html

15. Shock waves
When the source moves at or above the speed of the waves (vsource > vwave­)
Shock wave of a bullet in flight.

16. P3. 10-5 W/m2 has a dB level of _______ dB
P W/m2 has a dB level of _______ dB. A: 5 B: 50 C: 70 D: 80 E: 90 P4. A siren emitting at 200 Hz is on a car going very fast toward you at ½ the speed of sound (take the speed of sound to be 300 m/s here). You travel away from the car on your bike at 1/3 the speed of sound. The frequency you hear is_­­­_________ Hz A: 150 B: 200 C: 250 D: 267 E: 330

17. From two sounds with slightly different f’s.
Beats
From two sounds with slightly different f’s.
Applications of beats: Tuning Measuring Doppler shifts in radar, ultrasound