1. Waves, Sound and Light
Wave Properties

2. What is a wave?
Disturbance or vibration that transmits energy but not matter
Examples…
Sound, light, radiowaves, earthquakes

3. Types of Waves Mechanical Waves- Use a medium
Transverse waves- particles move perpendicular to wave motion
Longitudinal Waves- particles move parallel to wave motion
A longitudinal wave example is when you compress or stretch the spring. Remember a wave is motion of energy.
A medium is substance the wave is transported in.

4. Parts Of A Wave Crest-top of the wave Trough- Bottom of the wave
Amplitude (A)-height from resting position
Wavelength (λ)- distance travelled by a single wave
On a longintunal Wave- crests- compressed regions troughs- stretched regions wavelength is still crest to crest or trough to trough

5. Frequency and Period
Period (T)- time for one complete cycle or wavelength (in s)
Frequency (f)- number of waves per second (Hertz, Hz)
Hertz=1/s or s-1
Frequency and period are reciprocals of themselves
f= 1/T
T= 1/f
They are inversely
proportional

6. Example
Playing middle C on a piano produces a sound with a frequency of 256 Hz. What is the period of the sound wave?
f= 256 Hz
T=?
T=1/f
T=1/256
T=0.004 s
A hertz is 1/s, so when you take the reciprocal of frequency the unit is converted into seconds

7. Speed of Waves Remember V=d/t
So to get speed we need distance and time
A single wave
Distance travelled is one wavelength, λ
Time is one period, T
Velocity of a wave=wavelength x frequency
v=λf
Remember f=1/T

8. Example
An air horn sound at a frequency of 220 Hz. If the speed of sound in air is 330 m/s, what is the wavelength of the sound wave?
1.5 m

9. Example
The distance between successive crest in a series of water is 4.0 m, and the crests travel 8.6 m in 5.0 seconds. Calculate the frequency of a block of wood bobbing up and down on these water waves.
λ= 4.0 m
d=8.6 m
t=5.0 s
f=?
V=λf
V=d/t
V= 8.6/5
V=1.72 m/s
1.72=4f
f= 0.43 hz

10. Waves
Interference

11. Interference
Two different material objects can not occupy the same space at the same time
Waves are not matter but they can displace matter
Waves can occupy the same place at the same time
When waves overlap it is called superposition

12. Constructive Interference
Two waves superimposing that are on the same side of equilibrium
They will enhance each other or add up
Same side of equilibrium- they are both on the top
In the first and last image- notice that after they superimpose they return to their original state

13. Destructive Interference
Waves are on opposite sides of equilibrium
They will weaken each other or subtract

14. Standing Waves A wave that remains in constant position
Can occur when a medium is moving in the opposite direction or when two waves interfere with each other, or constructive and destructive interference

15. Reflection From a Boundary
When waves hit a boundary the wave will be reflected
If the boundary is fixed the wave will be reflected AND INVERTED
If the boundary is free the wave will just be reflected
A free boundary- a rope that is loosely tied to a pole, it is able to rotate

16. Standing Waves
If a series of waves are sent along a string the reflected pulse will interfere with itself
If the waves are sent at just the right frequency we will create a standing wave
Maximum Wavelength on a standing wave is 2L
Both ends have to be nodes
The possible wavelengths here are 2L (b) This is only ½ of a wave so the wavelength is twice the length of the string, L (c) this is a full wave and the length of the string is equal to one wavelength, and 2/3L (d) this is 1 and ½ waves, so the wavelength is 2/3 the length of the string

17. Antinodes and Nodes
Areas of complete destructive interference have NO amplitude are nodes
Areas of complete constructive interference have LARGE amplitudes are antinodes

18. Waves
Sound

19. Sound Begins with a vibrating object Is a longitudinal wave
The compression is where density and pressure are at a maximum (crest)
The rarefaction is the region are the minimum points (trough)

20. Sound Characteristics
Needs a medium to travel
The higher the temperature the faster
Higher temp=more energy=more vibrations
The more dense the faster
Vibrations will occur more quickly if the molecules are closer together
Pitch is determined by frequency
Volume is determined by amplitude

21. Clicker Question Which statement is true?
A) If a tree fell in outer space no one can hear it
B) A dog whistle has produces sounds that have a high amplitude
C) If you are at a concert all of the sound waves have a high frequency
D) Sound travels faster in air than water
A Sound can not travel in a vacuum or space! It needs a medium
B- pitch= high frequency
C- Loud=high amplitude
D- water=denser so the sound waves travel faster

22. Clicker question Which medium would have faster sound waves?
A) Gas (at 0 degrees)
B) Liquid (at 0 degrees)
C) Solid (at 0 degrees) C

23. Minimum and Maximum Frequency
Frequency pertains to pitch not loudness
Minimum- 20 Hertz
Below- infrasonic waves
Maximum- 20,000 Hertz
Above-ultrasonic waves
What are the corresponding wavelengths if the speed of sound in air is 343 m/s?

24. The Doppler Effect
When there is movement involved there is an observed change in frequency
This can be seen with all types of waves
Imagine a bug bouncing up and down on the water, now imagine that bug skimming along the surface of the pond. The waves in back have a longer wavelength and a lower f, the waves in front have a shorter wavelength and a higher frequency

25. The Doppler Effect
You hear a high pitch as an ambulance approaches you and as soon as it passes the pitch decreases suddenly
Compared to the noise being right beside you
It has a higher pitch as it approaches you
It is a lower pitch when it moves away from you
Radar guns work with the doppler effect too.
The radar hits the

26. The Red Shift Red light has the longest wavelength (colors)
When we look at other galaxies we notice that their colors are shifted towards red
This is due to the Doppler effect
What does this indicate?
The universe is expanding
Speed of a radar gun can be estimated by measuring the difference in frequency between emitted and reflected radar waves

27. Resonance
Objects/Substances can have a natural frequency in which it will begin to vibrate when that frequency strikes the object
If another object begins emitting that wave at that natural frequency then the second object will begin to vibrate at the same frequency
Example opera singer shattering glass, musical cups

28. Standing Waves/Harmonics
On a string standing waves are made
b-1st harmonic
natural frequency
c-2nd harmonic
1st overtone
One octave higher
d-3rd harmonic
2nd Overtone

29. Electromagnetic Waves and Light

30. Types of Waves Mechanical Waves Use a Medium
Traverse (ocean waves) and Longitudinal (springs and sound)
Electromagnetic Waves
Do not require a medium
Are transverse waves
Are formed when an electric field is coupled with a magnetic field
Light, microwaves, radiowaves etc

31. Electromagnetic Spectrum
Rabbits Mate In Visible Unusual eXspensive Gardens
Radio, Microwaves, Infrared, Visible, Ultraviolet, X-rays, Gamma Rays
ROYGBIV
Red, orange, yellow, green, blue, indigo, and violet

32. Visible Light White light is a mixture of different colors
Red light has the longest wavelength (700 nm)
Violet has the shortest (400 nm)
ROYGBIV

33. EM Radiation Is emitted from energized matter
After energy is absorbed by matter it is emitted as EM radiation

34. Speed of Light The speed of light=c
The speed of light is 3.0 x 108 m/s in a vacuum
IF there is a medium the speed will depend on the type of medium
Denser=slower

35. Example
The sun is 1.50 x 108 km from Earth. How long does it take for the light from the Sun to reach us?
d=1.50 x 108 km
d=1.50 x 1011 m
c=3.0 x 108 m/s
t=?
v=d/t
500 seconds or 8.3 min

36. Example
What is the frequency of red light if the wavelength is 700 nm?
λ=700 nm
λ=7.0 x 10-9 m
c=3.0 x 108 m/s
f=?
v=λf
c=λf

37. Waves, Sound and Light
Snell’s Law

38. Wave Speed Wave Speed depends on the medium
When waves travel from one medium into another the speed will change
As the waves moves to more shallow water the waves slow down

39. Wave Speed
Waves traveling perpendicular to the new medium (θi=0 or angle of incidence) continue in the same direction
Velocity changes, but the frequency stays constant
Soo.. Wavelength will change
When waves are not perpendicular they will bend

40. Refraction Refraction-bending of a wave due to changing medium
Optical Density- a measure of how difficult it is for light to travel in a substance
Vacuum<air<water<glass<diamond

41. Angles Angle of Incidence Angle of refraction
Angle between the incident ray (original wave/ray) and the normal
Angle of refraction
Angle between the refracted ray and the normal

42. Snell’s Law When light travels from
Less dense to more dense medium it slows down and bends towards the normal
More dense to less dense medium it speeds up and bends away from the normal

43. Snell’s Law nisinθi=nrsinθr ni=index of refraction (first medium)
θi=angle of incidence
nr=index of refraction (second medium)
θr=angle of refraction

44. Index Medium n Vacuum 1 Crown glass 1.52 Air 1.0003 Quartz 1.54 Water
1.33
Flint Glass
1.61
Ethanol
1.36
Diamond
2.42

45. Example
A ray of light traveling in air strikes a block of quartz at an angle of 15 degrees. Find the angle of refraction. Draw a diagram.

46. Example
A ray of light travels from underwater into air. It travels in the air at an angle of 65 degrees, find the incident angle. Draw a diagram.

47. Index of Refraction n=c/v n=index of refraction
c=speed of light in vacuum 3.0 x108 m/s
v= speed of light in substance

48. Example What is the speed of light in water? c=3.0 x 108 m/s n=1.33
v=?
n=c/v

49. Total Internal Reflection
When passing from a more dense to a less dense medium, light reflects away from the normal
If the angle of large enough then the angle of refraction will be parallel to the medium boundary (θr=90 degrees)

50. Critical Angle Critical Angle- θi that results in θr = 90
Total internal reflection- the wave does not pass into the next medium, occurs when θi>θc

51. Example
Find the Critical angle for light traveling from water into air. Draw diagram
ni=1.33
nr=1.0003
θr=90
θc=? Or θi
nisinθi=nrsinθr

52. Waves, Sound, and Light
Reflection

53. Reflection
When a wave travels into a new medium some will be reflected back
The amount of reflection will depend on different the media are

54. Law of Reflection
Light reflected from a plane (flat) mirror follows this law
Angle of Incidence= Angle of Reflection
θi=θr
These angles are measured from the normal, the line perpendicular to the mirror

55. Ray Diagram- Flat (Plane)Mirror

56. Regular Reflection Versus Diffuse Reflection
Does not reflect an image
You can see a reflected image

57. Plane Mirror Ray Diagrams
When you look at an image in a plane mirror it is
The same size
The same distance behind the mirror as you are in front of it
Right side up and laterally inverted
The reflected light has the same speed, wavelength and frequency as the incident light

58. Curved Mirrors
Concave- curved inwards
Convex-curved outwards

59. Ray Diagrams
Convex
Concave

60. Definitions Principal Axis- Line through the center of the mirror
Center of Curvature (C)-center of spherical mirror (center of the circle if the mirror was a complete circle)
Focal Point (F)- point where all light converges (all rays pass this point)
Focal length (f) distance from F to mirror and from C to F

61. Find the focal point

62. Focal Length 1 = 1 + 1 f do di f=focal length
do = distance of object from mirror
di= distance of image from mirror
Can be used for mirrors and lenses

63. Example
An object is 15 mm in front of a concave mirror, and the image is 4.0 mm behind the lens. What is the focal length of the lens?
do=15 mm
di = 4 mm
f=?
1 = 1 + 1
f do di
1/f=1/15 + 1/4
1/f=.3166
f=3.15 mm

64. Diffraction and Polarization
Diffraction- waves can bend around objects
White light can be split into multiple colors, with a diffraction grating in a prism