1. Waves

2. Energy may spread out as a wave travels.
WAVE: periodic disturbance that transfers energy through space, matter, and time.
Energy may spread out as a wave travels.
When sound waves travel in air, the waves spread out in spheres. As they travel outward, the spherical wave fronts get bigger, so the energy in the waves spreads out over a larger area.

3. 2 Main Types of Waves MECHANICAL WAVES: require a medium.
Matter through which a wave travels is called the medium (air, water, earth, rope, metal, etc)
ELECTROMAGNETIC WAVES: do not require a medium (can travel in a vacuum).
Light waves consist of changing electric and magnetic fields in space.
Travel at the speed of light (~300,000,000 m/s in a vacuum)

4. 2 Ways Waves are Shaped/Transport Energy
LONGITUDINAL WAVE: wave in which the particles of the medium vibrate parallel to the direction of wave motion.
Sound waves and seismic P-waves are longitudinal.
TRANSVERSE WAVES: wave in which the particles of the medium move perpendicular to the direction the wave is traveling.
Light waves and seismic S-waves are transverse.

5. THINK! What are the 2 ways waves carry energy? sketch each.
What is a ‘medium’ in your own words?

6. Parts of a Transverse Wave
An ideal transverse wave has the shape of a sine curve
CREST = highest point of a transverse wave.
TROUGH = lowest point of a transverse wave.
AMPLITUDE = maximum distance that the particles of a wave’s medium vibrate from their rest position.
The energy of a mechanical wave is related to the amplitude.
WAVELENGTH (λ) = distance from any point on a wave to an identical point on the next wave.

7. Frequency – Wavelength Relationship
FREQUENCY = number of complete waves (or cycles) per unit of time (usually seconds).
The symbol for frequency is f.
The SI unit for measuring frequency is hertz (Hz).
Frequency – Wavelength Relationship
Shorter wavelength = higher frequency = more energy
Longer wavelength = lower frequency = less energy
Wavelength =
Frequency =
6 cm
2 Hz
3 cm
1 second
Wavelength =
Frequency =
12 cm
1 Hz
3 cm
1 second

8. Speed of a mechanical wave depends on the medium.
MECHANICAL WAVE SPEED
Speed of a mechanical wave depends on the medium.
Mechanical waves generally travel:
fastest in solids
moderate in liquids
slowest in gases
ELECTROMAGNETIC WAVE SPEED
All electromagnetic waves in empty space (a vacuum) travel at the speed of light, which is 300,000,000 m/s (186,000 mi/s).
EM waves travel slower in a medium

9. 2.5 cm
Wavelength = _________
Amplitude = ___________
Frequency = __________
5 cm
4 cm
4 cm
4 Hz
5 cm
8 cm
Wavelength = _________
Amplitude = ___________
Frequency = __________
10 cm
8 cm
2 Hz
10 cm
Wavelength = _________
Amplitude = ___________
Frequency = __________
20 cm
2 cm
2 cm
1 Hz
1 Second

10. THINK!
What is the relationship between wavelength and frequency?

11. Exit Ticket: Parts of a Wave
#17

12. 17. Which letter indicates wavelength? A B C D

13. 18. Which letter indicates trough? A B C D

14. 19. Which letter indicates Amplitude? A B C D

15. 20. Which letter indicates crest? A B C D

16. Four Defining Properties of Waves plus Polarization and Doppler Effect

17. #1 REFLECTION: The bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through (echo, mirror image, etc.).
#2 DIFFRACTION: The bending of waves around an edge.

19. # 3 REFRACTION: Bending of waves when passing from one medium to another at an angle
Caused by a change in speed of the wave
White light disperses into the separate colors (ROYGBIV) in a prism or raindrop

22. Waves in the same place combine to produce a single wave…
#4 INTERFERENCE: Combination of two or more waves of the same frequency that results in a single wave.
Resulting wave can be found by adding the amplitude of the waves at each point.
Crests are considered positive, and troughs are considered negative.
Principle of SUPERPOSITION: When 2 waves interfere, the resulting wave is a combination of the first 2 waves

23. CONSTRUCTIVE INTERFERENCE: waves combine so that the resulting wave is bigger than the original waves; the amplitude increases.
DESTRUCTIVE INTERFERENCE: waves combine so that the resulting wave is smaller than the largest of the original waves; the amplitude decreases.
Waves can cancel each other out (sound canceling headphones)

24. Applications of Wave Properties
Color on Soap Bubbles
Result of interference and double reflection
Rainbows
Refraction – Reflection – Refraction
Fiber optics
Use total internal reflection
TIR = complete reflection that takes place within a substance when the angle of incidence of light striking the surface boundary is less than the critical angle.

29. Blue Sky & Red Sunsets Molecules in atmosphere scatter light rays.
NOON
less atmosphere
less scattering
blue sky, yellow sun
Shorter wavelengths (blue, violet) are scattered more easily.
SUNSET
more atmosphere
more scattering
orange-red sky & sun

30. Polarization (Property of Light Waves)
Causing light waves to be oriented in a single plane

31. Frequency changes when the source of waves is moving.
The pitch of a sound (how high or low) is determined by the frequency at which sound waves strike the eardrum in your ear.
Higher-pitched sound is caused by sound waves of higher frequency and vice-versa.
Frequency changes when the source of waves is moving.
Doppler effect = observed change in the frequency of a wave when the source or observer is moving.
Shorter wavelengths/high frequency in front of the moving source
Longer wavelengths/low frequency behind the moving source

32. Understanding Concepts
Chapter 14
Understanding Concepts
1. Which of the following waves can be transmitted without a medium?
A. electromagnetic
B. longitudinal
C. mechanical
D. transverse

33. Understanding Concepts
Chapter 14
Understanding Concepts
1. Which of the following waves can be transmitted without a medium?
A. electromagnetic
B. longitudinal
C. mechanical
D. transverse

34. Understanding Concepts
Chapter 14
Understanding Concepts
2. How do longitudinal waves carry energy from a source?
F. Particles vibrate outward from the source of the wave.
G. Particles vibrate parallel to the direction of the wave.
H. Particles vibrate perpendicular to the direction of the wave.
I. Particles vibrate both parallel and perpendicular to the direction of the wave.

35. Understanding Concepts
Chapter 14
Understanding Concepts
2. How do longitudinal waves carry energy from a source?
F. Particles vibrate outward from the source of the wave.
G. Particles vibrate parallel to the direction of the wave.
H. Particles vibrate perpendicular to the direction of the wave.
I. Particles vibrate both parallel and perpendicular to the direction of the wave.

36. Understanding Concepts
Chapter 14
Understanding Concepts
3. What is measured by the amplitude of a wave?
A. the amount of vibration of particles
B. the direction of vibration of particles
C. the rate of vibration of particles
D. the wavelength of vibration of particles

37. Understanding Concepts
Chapter 14
Understanding Concepts
3. What is measured by the amplitude of a wave?
A. the amount of vibration of particles
B. the direction of vibration of particles
C. the rate of vibration of particles
D. the wavelength of vibration of particles

38. Understanding Concepts
Chapter 14
Understanding Concepts
4. Which combination of wave interactions can cause a standing wave?
F. diffraction and interference
G. diffraction and reflection
H. reflection and interference
I. reflection and refraction

39. Understanding Concepts
Chapter 14
Understanding Concepts
4. Which combination of wave interactions can cause a standing wave?
F. diffraction and interference
G. diffraction and reflection
H. reflection and interference
I. reflection and refraction

40. Understanding Concepts
Chapter 14
Understanding Concepts
5. Why do astronauts on the moon need a radio transmitter to carry on a conversation with each other?

41. Understanding Concepts
5. Why do astronauts on the moon need a radio transmitter to carry on a conversation with each other?
Answer: Sound waves require a medium to carry energy from one place to another. On the moon, there is no air to carry the vibrations.

42. Reading Skills
The Doppler Effect applies to light as well as sound. Astronomers have used this fact to measure the speed of objects in space as they move away from Earth. They know the frequency and wavelength of the light as it leaves a star because the energy transitions in atoms are the same throughout the universe. When the light reaches Earth, it has a different frequency from when it left the star.
6. Assess how the knowledge that light always travels at the same speed is essential for determining the speed at which a distant galaxy and Earth are moving apart.

43. Reading Skills
6. Assess how the knowledge that light always travels at the same speed is essential for determining the speed at which a distant galaxy and Earth are moving apart.
Answer: Using the change in frequency of light and the fact that the speed of light is constant, astronomers can calculate how fast the objects are moving away from one another.

44. Reading Skills
The Doppler Effect applies to light as well as sound. Astronomers have used this fact to measure the speed of objects in space as they move away from Earth. They know the frequency and wavelength of the light as it leaves a star because the energy transitions in atoms are the same throughout the universe. When the light reaches Earth, it has a different frequency from when it left the star.
7. Astronomers have observed that the wavelength of light reaching Earth from one edge of the sun is slightly different than from the other edge. What can be concluded about the sun based on this observation?

45. Reading Skills
7. Astronomers have observed that the wavelength of light reaching Earth from one edge of the sun is slightly different than from the other edge. What can be concluded about the sun based on this observation?
Answer: The observation indicates that the sun is rotating. The light from one edge is shifted to a shorter wavelength, and light from the other edge is shifted to a longer wavelength.

46. Interpreting Graphics
8. What wave phenomenon is demonstrated in this illustration?
A. diffraction C. reflection
B. Interference D. refraction

47. Interpreting Graphics
8. What wave phenomenon is demonstrated in this illustration?
A. diffraction C. reflection
B. Interference D. refraction

48. Interpreting Graphics
9. Which of the points on the illustration indicates an antinode?
F. W H. Y
G. X I. Z

49. Interpreting Graphics
9. Which of the points on the illustration indicates an antinode?
F. W H. Y
G. X I. Z

50. Light comes in a wide range of frequencies and wavelengths.
Wave Properties
Light comes in a wide range of frequencies and wavelengths.
Our eyes can detect light with frequencies ranging from about 4.3  1014 Hz to 7.5  1014 Hz.
Light in this range is called visible light.
The full range of light at different frequencies and wavelengths is called the electromagnetic spectrum.