1. Thursday PS 1-3
Homework
Light
Sound

2. Homework Pg 478
1) Describe what may happen when ripples on a pond encounter a large rock
2) Explain why you can hear two people talking even after they walk around a corner?
3) Name the conditions required for two waves to interfere constructively

3. Homework P 478 4) Explain why colors appear on a soap bubble
5) Draw a standing wave, and label nodes and antinodes
6) What conditions are required for two waves to interfere completely destructively? (there are 4)

4. Answers Reflection Diffraction, as they pass the corner of hall
Waves must be in same place (meet). Crest meets crest or trough meets trough

5. Answers
4) Two sets of reflected waves from bubble meat, some constructively, others destructively changing the wavelength of light. Different colors result from different wavelengths 5)
6) Waves must match in amplitude, frequency and crest must match up with trough

6. Correction
Colors can be formed by either constructive or destructive interference
As long as the combined frequency falls within the range of visible light
Different frequencies of light produce color

7. Iridescence
Also formed as a result of interference between 2 or more waves of light
Liquid crystal thermometers
Wings of butterflies
Tail of a peacock
Bird feathers
Beetles shell

8. Examples of Iridescence

9. More examples of iridescence

10. SOUND

11. Sound Wave type –Longitudinal Speed of Sound 331m/s @ 0°C to 386 @ 25C
C in water C
Speed of sound is effected by temperature, and type of medium

12. Other measurement of sound
Intensity

13. Loudness Depends on the energy in the sound wave
Intensity = rate of energy transmission through a given area of the medium
Greater Intensity  Louder sound

14. Measure of Loudness Relative intensity
Compares the intensity of the sound with the intensity of the quietest sound that a person can hear
Measured in decibels

15. Decibel scale 0 dB  threshold of hearing 30 dB  whispering
50dB  normal conversation
70dB  vacuum cleaner
90 dB  lawnmower
120 dB  threshold of pain
150 dB  nearby jet airplane

17. Pitch Not related to loudness Related to the frequency of wave
The higher the frequency
 higher the pitch
Humans can hear a range of sound from 20 HZ to 20,000 HZ

18. Sound beyond human range
Lower than 20 Hz  Infrasound
Higher than 20,000 Hz  ultrasound
Dogs can hear to 46,000 Hz
Dolphins can hear to 150,000 Hz

19. Elephant communication
Use infrasound waves between 6-18Hz
Few objects can absorb the energy carried by these frequencies
Sounds heard across far distances

20. Echo-location Dolphin sends out a series of audible clicks.
They bounce off an object and reflect back to dolphin, received by 2 ears
Through experience, dolphin relates time, strength of signal into distance

21. Other animals to use echo-location

22. Musical Instruments
Produce sound by vibrating strings, air columns or membranes
Changing where you press on a string, The length of the air column changes the frequency, and pitch
Standing waves produce the continuous sound,
Notes created at certain wavelengths

23. Echos
What is needed to create an echo?

24. Place where you hear an echo the most?

25. Example of Ultrasonic sound waves
                                      
Example of Ultrasonic sound waves
1 to 15 million Hz
Passes through most materials, but reflects at medium boundaries
Not harmful like
x-rays
Used more frequently for other purposes

26. Why use ultrasonic waves?
Focused into more narrow beams
Directed more easily

27. SONAR Sound, Navigation, and RAnging
Uses acoustic signals and echo returns to locate objects

28. Sonar

29. Homework
Pg 498
Problems 1-5 and #9