Chapters 10 & 11

1. Chapters 10 & 11 Waves, Sound and Light

2. Discussion Questions What is the brown noise (note)? Does it exist? How does a ninja (silent) ringtone work? After you drop a rock into a lake, explain how the waves move the water?

3. Waves • What is a wave? • Vibration that occurs in a certain amount of time • Simple harmonic motion – up and down or back and forth • Movement of energy only, matter does not move!

4. Types of Waves • How are the two main types of waves different? • Transverse • Wave motion is at right angles to the direction of the wave • Ex. Radio waves • Longitudinal • Wave motion follows the direction of the wave • Ex. Sound waves

5. Types of Waves • How are the two main types of waves similar? • All waves transfer energy regardless of their type

6. Wave Properties • What are the main parts of a transverse wave? • Crest • Top • Peak • Trough • Lowest point • Valley • Together they make a sine wave

7. Wave Properties • What are the parts of a longitudinal wave? • Compression – material is close together • Rarefaction – material is farther apart

8. Wave Properties • How can we measure a wave? • Amplitude (A) • Half the distance between the crest and trough of the wave • Wave “height” • Wavelength (λ) • Horizontal distance between identical adjacent points on a wave, usually crest to crest

9. Wave Properties

10. Wave Properties • What is frequency? • Frequency (f) • Number of waves in a given period of time, usually one second • Unit: Hertz – Hz or 1/s • Period (T) • Time it takes to move up and down • One crest and one trough Period = 1 / Frequency

11. Tone Generator Within what frequency range can a human hear?

12. Tone Generator • What is the sound called outside of that range? • What happens to human hearing as a person gets older? • Below 20 Hz = Infrasound • Above 20000 Hz = Ultrasound • Auditory system begins to worsen • Detectable frequency range becomes smaller, especially at higher end • Other causes include noise and bacteria

13. Tone Generator • What sound property affects amplitude? • What sound property affects wavelength and frequency? • Volume • Higher volume = Higher amplitude • Directly Proportional • Pitch • Higher pitch = Higher frequency • Directly Proportional • Higher pitch = Shorter wavelength • Indirectly Proportional

14. Wave Speed • What affects wave speed (v)? • The medium (space) through which it travels • Ex. Sound travels through air and water at different speeds • Temperature of a medium • v = (f)(λ) V f λ

15. Wave Practice • Sonar is a device that uses reflected sound waves to measure underwater depths. If a sonar signal has a frequency of 288 Hz and the speed of sound in water is 1450 m/s… • What is the wavelength of the sonar signal?

16. Wave Practice • A drum is struck, producing a wave with a wavelength of 1.10 m and a speed of 242 m/s. • What is the frequency of the wave? • What is the period?

17. Questions What is the brown noise (note)? Does it exist?

18. Questions How does a ninja (silent) ringtone work? After you drop a rock into a lake, explain how the waves move the water?

19. Types of Waves

20. Discussion Questions (Part 2) How do noise cancelling headphones work? Do How does police radar work? When an object goes faster than the speed of sound what happens?

21. Overlapping Waves • What happens when two waves overlap? • An interference pattern is created • Within an interference pattern waves can be increased, decreased or destroyed • Two types of interference: • Constructive • Destructive

22. Constructive Interference • How is constructive interference created? • When the crest (compression) of a wave overlaps with the crest (compression) of another • “In phase” • Increased amplitude • Also called reinforcement or amplification

23. Destructive Interference • How is destructive interference created? • When the trough (rarefaction) of a wave overlaps with the crest (compression) of another • “Out of phase” • Decreased amplitude • Also called cancellation

24. Destructive Interference

25. Interference • How does interference affect sound? • How do we fix interference? • Constructive interference builds amplitude = louder • Destructive interference decreases amplitude = softer • Acoustics

26. Acoustics

27. Interference Practice Combine the following two waves. What type of interference is created?

28. Interference - Beats • Why do two frequencies sometimes create a pulse or beat? • The two frequencies have to be close together • Interference creates alternations of loud and soft, or beats

29. The Doppler Effect • What happens to sound waves that come from a non-stationary source? • Doppler Effect • Waves in front of the source get bunched together • Shorter wavelength • Higher frequency • Waves behind the source are farther apart • Longer wavelength • Lower frequency

30. The Doppler Effect

31. The Doppler Effect • How does this affect light (EM) waves, since we cannot hear them? • Shift in color • Blue shift • Shorter wavelength • Higher frequency • Moving to • Red shift • Longer wavelength • Lower frequency • Moving away

32. Shock Waves • What happens when the sound waves in front of an object overlap? • A wave barrier is created • If the wave barrier is broken, a sonic boom occurs and the object becomes supersonic

33. Sonic Boom