1. Chapter 17 & 18 Waves

2. Mechanical Waves
Disturbance in matter that carries energy from one place to another
Medium: what a wave travels through
Can be a solid, liquid, or gas
Created when source of energy causes vibration to travel through a medium

3. Transverse Waves
Causes medium to vibrate at right angles to direction of wave
Travels left to right
Crest: highest point above rest position
Rest: before wave
Trough: lowest point below rest position

4. Longitudinal Waves
Vibration of the medium is parallel to direction of wave
Vibration is a back and forth motion
Ex: slinky, P-wave (earthquakes)

5. Rarefaction: particles are more spread out
Compression: particles in a medium are spaced close together

6. Surface Waves Travels along a surface separating two media
Carries energy from left to right
Ex: ocean waves

7. Properties of Mechanical Waves
Frequency and period
Periodic motion: repeats at regular time intervals
Period: time for one complete cycle
Frequency: number of complete cycles in a given temperature
Measured in hertz (Hz): cycles/second
Equals frequency of vibrating source producing wave

8. Wavelength
Distance b/w point on 1 wave and same point on next wave cycle
Increasing frequency decreases wavelength

9. Wave Speed Speed (m/s) = wavelength (m) x frequency (Hz)
Speed can change if in a new medium
Wavelength is inversely proportional to frequency
Longer the wavelength, shorter the frequency
Shorter the wavelength, longer the frequency

10. 1. The musical note A above middle C has a frequency of 440 Hz
1. The musical note A above middle C has a frequency of 440 Hz. If the speed of sound is
known to be 350 m/s, what is the wavelength of this note?
2. A certain FM radio station broadcasts electromagnetic waves at a frequency of 9.05 × 107 Hz. These radio waves travel at a speed of 3.00 × 108 m/s. What is the wavelength of these radio waves?

11. 3. A wave with a frequency of 60
3. A wave with a frequency of 60.0 Hz travels through vulcanized rubber with a wavelength of 0.90 m. What is the speed of this wave?
4. A wave with a frequency of 60.0 Hz travels through steel with a wavelength of 85.5 m. What is the speed of this wave?

12. Amplitude Maximum displacement of the medium from its rest position
More the energy wave has, the greater its amplitude

13. Wave Behavior
Reflection: wave bounces off a surface it cannot pass through
Does not change speed or frequency of a wave
Can flip wave upside down

14. Refraction: bending of a wave as it enters new medium at an angle
1 side moves more slowly than the other
Changes wave direction

15. Diffraction: bending of wave as it moves around an obstacle or passes through a narrow opening
Increase if wavelength is large compared to size of opening/obstacle

16. Interference: 2 or more waves overlap and combine together
2 types:
Constructive: increases amplitude
2 or more waves combine to make wave with a larger displacement
Destructive: reduces amplitude
Smaller displacement

17. Standing Waves Appears to stay in one place (does not seem to move)
Node: point that has no displacement from the rest position
Destructive interference b/w incoming and reflected waves
Antinode: point where a crest or trough occurs midway b/w 2 nodes
Only forms if ½ or a multiple of half a wavelength fits exactly into length of a vibrating cord

18. Sound and Hearing Properties of sound waves: Longitudinal waves
Speed: varies in different media
Travels faster in solids > liquids > gases
Intensity: rate at which a wave’s energy flows through a given area
Depends on wave’s amplitude and distance from sound source
Measured in decibels (tenfold increase with every 10-decibel increase)

19. Loudness: physical response to intensity of sound
Increases as intensity increases
Frequency: depends on how fast the source of the sound is vibrating
Pitch: frequency of a sound as you perceive it
Depends on wave’s frequency
High  high pitch
Low  low pitch

20. Ultrasound Sound at frequencies higher than most people hear
Used in sonar and imaging
Sonar: determines distance to an object under water
Name means “sound navigation and ranging”
Imaging used in medical techniques

21. Doppler Effect
Change in sound frequency caused by motion of the sound source, motion of listener, or both
Higher as it gets closer
Lower as it moves farther away

22. Electromagnetic Waves
Transverse waves of changing electric and magnetic fields (regenerate each other)
Carry energy from place to place
Electric field: exerts electric forces on charged particles

23. Wavelength and frequency: all waves vary
Speed = wavelength x frequency
Wavelength is inversely proportional to its frequency

24. Electromagnetic Spectrum
Types of waves that make up the spectrum:
Infrared, Radio, UV, X-Rays, and Gamma rays

25. Behavior of Light Transparent: transmits light (can pass through)
Translucent: scatters light (can see through material but objects not clear)
Opaque: absorbs or reflects all light that strikes it (none passes through)

26. When light strikes a new medium, it can be reflected, absorbed, or transmitted
Reflection
Smooth surface: clear, sharp image
Rough surface: blurred or no image

27. Transmitted light
Refraction: bending light wave can cause a mirage (false or distorted image)

28. Colors White light: made up of all colors of visible spectrum
Prism separates colors (dispersion)
Shorter wavelengths refract more than longer wavelengths

29. Color of objects is color of light that reaches your eye
Depends on what object is made out of and color of light that strikes the object