1. Chapter 16 Sound and Light

2. Sound
Sound wave: a longitudinal wave that is caused by vibrations and that travels through a material medium
A series of compressions and rarefactions
Carries energy through medium
All sound waves are made by vibrating objects that cause the surrounding medium to move

3. Sound

4. Sound The speed of sound depends on the medium
Depends on the temperature and the material through which the wave travels
Colder temperatures: slower
Warmer temperatures: faster
Gas (air):slower (346 m/s)
Liquids: faster than gas
Solids: faster than liquids
Some solids like rubber, dampen vibrations so that sound does not travel well (materials like rubber are used for soundproofing)

5. Sound
Speed depends on the temperature and the material through which the wave travels

6. Sound

7. Sound

8. Sound

9. Sound Loudness is determined by Intensity
Intensity depends on the amplitude of the sound wave and your distance from the source of the sound
Greater the intensity, the louder the sound
Humans perceive loudness on a logarithmic scale
A sound seems twice as loud when its intensity is 10 times the intensity of another sound
Intensity is measured in units called decibels (dB)
An increase in intensity of 10 dB means a sound seems about twice as loud

10. Sound

11. Sound

12. Sound The quietest sound a human can hear is 0 dB
A sound of 120 dB is at the threshold of pain
Above this value could cause permanent deafness

13. Sound

14. Sound Pitch is determined by frequency
Pitch is a measure of how high or low a sound is and depends on the sound wave’s frequency
A high-pitch sound is made by something vibrating rapidly (high frequency)
A low-pitch sound is made by something vibrating slowly (low frequency)

15. Sound

16. Sound

17. Sound

18. Sound Humans hear sound waves in a limited frequency range
Frequency of 20Hz to 20,000Hz
Frequency below the range of human hearing is infrasound
Frequency above the range of human hearing is ultrasound

19. Sound

20. Sound
Musical instruments: produce sound through the vibration of strings, air columns, or membranes
Strings: when you pluck the string on a guitar, particles in the string vibrate.
Sound travels out to the ends of the string and then reflect back toward the middle thus causing a standing wave on the string
The two ends of the string are called nodes, and the middle of the string is called an antinode
Standing wave exist only at certain wavelengths on a string: fundamental frequency
Primary standing wave on a vibrating has a wavelength that is twice the length of the string

21. Sound

22. Sound
You can change the pitch by placing your finger on the string anywhere on the guitar’s neck
A shorter length of string vibrates more rapidly, and the standing wave has a higher frequency with a resulting higher pitch

23. Sound All musical instrument produce standing waves
Drum: standing waves formed on the membranes vibrate
Wind instruments: standing waves form in the column of air
Opening and closing holes changes the length of the air columns, which change the wavelength and frequency of the standing waves

24. Sound

25. Instruments Instruments use resonance to amplify sound
when one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion.
String and guitar body are vibrating at the same frequency
Amplifies the sound
Electric guitars do not resonate well and must be amplified electronically

26. Sound

27. Sound
The human ear is a sensitive organ that senses vibrations in the air, amplifies them, and then transmits signals to the brain
Sound waves travel through the outer ear (auditory canal) and cause the eardrum to vibrate
The vibration passes from the eardrum through the three small bones of the middle ear (hammer, anvil, stirrup)
Stirrup vibrates the membrane of the inner ear (oval window) sending the wavelength through the spiral-shaped cochlea
The cochlea contains a long, flexible membrane called the basilar membrane
Different parts of the membrane vibrate at different frequencies
Hair cells stimulate nerve fibers sending impulses to the brain

28. Sound
Reflected sound waves are used to determine distances and to create images
Ultrasound travel through most materials and some are reflected when they pass from one type of material into another
Sonar (sound navigation and ranging)is a system used to locate objects underwater

29. Sound

30. Sound

31. The Nature of Light
Waves and Particles: it is difficult to describe all the properties of light with a single model
The two most common models describe light as a wave or as a stream of particles

32. The Nature of Light
Light produces interference patterns as water waves do

33. The Nature of Light
The model of light as a wave is still used today to explain many of the basic properties of light and light’s behavior
Transverse waves that do not require a medium in which to travel
Transverse waves described by their amplitude, wavelength, and frequency
Light waves are also called electromagnetic waves because they consist of changing electric and magnetic fields

34. The Nature of Light
The particle model of light can explain some effects that the wave model cannot explain
Red light cannot knock electrons off the metal plate
Blue light can knock electrons off the metal plate
The wave model of light cannot explain this phenomenon

35. The Nature of Light
In the particle model of light beam of light is a packet of particles (photons)
Not like ordinary matter
No mass
They are little bundles of energy

36. The Nature of Light The model of light used depends on the situation
Wave model: can explain interference
Particle model: explains how light can travel across empty space without a medium

37. The Nature of Light
The energy of light is proportional to frequency of the electromagnetic wave

38. The Nature of Light The speed of light depends on the medium
Resented by the symbol: c
3 x 108m/s ( about 186,000 mi/s)
When light passes through a medium, such as air, water, and glass, it travels slower than it does in a vacuum

39. The Nature of Light The brightness of light depends on intensity
Intensity depends on the number of photons per second, or power, that pass through a certain area of space
Decreases as distance from the light source increases

40. The Nature of Light
Electromagnetic Spectrum: consists of waves at all possible energies, frequencies, and wavelengths

41. The Nature of Light Radio waves: TV, AM/FM radio, radar
Microwaves: cell phones, ovens
Infrared: heat lamps
Ultraviolet: sunburn, insect vision
X-rays. Gamma rays: medical functions

42. The Nature of Light

43. Reflection and Color
Every object reflects some light and absorbs some light
It is useful to another model for light, the light ray, to describe reflection, refraction, and many other ways light behaves
A light ray is an imaginary line running in the direction that the light travels or path of photons

44. Reflection and Color Reflection of Light:
Rough surfaces reflect light rays in many directions
Smooth surfaces reflect light rays in one direction
Law of reflection:The angle of the light rays reflecting off the surface, called the angle of reflection, is the same as the angle of the light rays striking the surface, called the angle of incidence
Both of these angles are measured from a line that is perpendicular to the surface at the point where the light hits the surface (normal)

45. Reflection and Color

46. Reflection and Color

47. Reflection and Color

48. Reflection and Color

49. Reflection and Color
Mirrors reflect light as described by the law of reflection, and this light reaches your eyes.
The type of image you perceive depends on the type of mirror
Virtual image: an image from which light rays appear to diverge, even though they are not actually focused there
Cannot be projected on a screen
Real image: an image that is formed by the intersection of light rays
Can be projected on a screen

50. Reflection and Color
Most mirrors are made by coating a piece of glass with a layer of metal. The glass provides the smooth surface necessary for good reflection and protects the metal from becoming scratched and tarnished. Polished plate glass is used for the finest mirrors. A solution containing silver nitrate is poured onto the glass, and a deposit of silver adheres to the glass. The remains of the solution are poured off and the glass is dried. The silvered surface (the back of the mirror) is then coated with a protective substance, such as shellac, to keep the silver from being rubbed off or scratched.

51. Reflection and Color

52. Reflection and Color
Curved mirrors: imagines created are distorted

53. Reflection and Color Convex: bulge out Images smaller
Passenger side mirror

54. Reflection and Color
Convenience store mirrors are convex. Convex mirrors will produce upright virtual images that are smaller than the object. Their benefit is that they allow you to see more area in the reflection.

55. Reflection and Color
Concave: indented
Images larger

56. Reflection and Color
Make up mirrors are concave. Concave mirrors will produce upright, magnified virtual images if the object is between the focal point and the mirror.

57. Reflection and Color
Seeing colors: the colors that you perceive depend on the wavelengths of visible light that reach your eyes
Objects have the color of the wavelength they reflect
Example:
Green leaf reflects green wavelength and absorbs the other wavelengths
White: reflects all wavelengths
Black: absorbs all wavelengths

58. Reflection and Color

59. Reflection and Color

60. Reflection and Color Mixture of colors produce other colors
Additive Primary Colors: red, green, and blue
Mixing light of two of these colors produces the secondary colors yellow, cyan, and magenta
Mixing light of the three primary colors produces white light

61. Reflection and Color

62. Reflection and Color
Because filters and pigments absorb light, the opposite effect happens when they are mixed.
The Subtractive Primary Colors-yellow, cyan, and magenta-can be combined to create red, green, and blue
If filters or pigments of all three colors are combined in equal proportions, all visible light is absorbed
No light gets to your eyes, so you see black
Black is not a color, it is the absence of color

63. Reflection and Color

64. Refraction, Lenses, and Prisms
Light waves bend, or refract, when they pass from one transparent medium to another

65. Refraction, Lenses, and Prisms
When light moves from a material in which its speed is high to a material in which its speed is lower, such as from air to a glass the ray is bent toward the normal

66. Refraction, Lenses, and Prisms
If light moves from a material in which its speed is low to one in which its speed is higher, the ray is bent away from the normal

67. Refraction, Lenses, and Prisms
Refraction makes objects appear to be in different positions

68. Refraction, Lenses, and Prisms

69. Refraction, Lenses, and Prisms

70. Refraction, Lenses, and Prisms

71. Refraction, Lenses, and Prisms
A mirage is a virtual image that is caused by refraction of light in the atmosphere
The air temperature affects the speed at which light travels. When light from the sky passes into the layer of hot air just above the asphalt on a road, the light refracts and bends upward away from the road. This refraction creates a virtual image of the sky coming from the direction of the road. Your mind visualizes water.

72. Refraction, Lenses, and Prisms

73. Refraction, Lenses, and Prisms

74. Refraction, Lenses, and Prisms
Lenses: when light passes through a medium that has a curved surface, a lens, the light rays change direction.

75. Refraction, Lenses, and Prisms
Convex lens: converging lens
When light rays pass through a lens that is thicker in the middle, the rays are bent inward

76. Refraction, Lenses, and Prisms
Concave lens: diverging lens
When light rays pass through a lens that is thicker at the ends, the rays are bent outward

77. Refraction, Lenses, and Prisms
Microscope use a series of convex lens to magnify the specimen
Image

78. Refraction, Lenses, and Prisms
Human eye depends on refraction and lenses

79. Refraction, Lenses, and Prisms

80. Refraction, Lenses, and Prisms
Prism: separates white light into its component colors
Air droplets in the air can also separate the color in white light to produce a rainbow

81. Refraction, Lenses, and Prisms
Different colors of light are refracted by different amounts
Light waves travel at 3.0 x 108 m/s in a vacuum
When a light wave travels through a medium, the speed of the light waves depends on the light wave’s wavelength
Violet waves have a shorter wavelength and travel slowest
Red waves have a longer wavelength and travel the fastest
Because violet light travels slower than red light, violet light bends more than red light when it passes from one medium to another
This effect is called dispersion

82. Refraction, Lenses, and Prisms
Rainbows are caused by dispersion and reflection