Chapter: Sound and Light

Transcription

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2 Table of Contents Chapter: Sound and Light Section 1: Sound Section 2: Reflection and Refraction of Light Section 3: Mirrors, Lenses, and the Eye Section 4: Light and Color

3 1 Sound Sound When an object vibrates, it creates sound waves. Sound waves are compressional waves. The compression moves away as these molecules collide with other molecules in air. A rarefaction is formed where the molecules are farther apart. This series of compressions and rarefactions is the sound wave that you hear.

4 1 Sound Sound The material in which a sound wave moves is called a medium. Sound waves travel in solids, liquids, and other gases as a vibrating object transfers energy to the particles in the material.

5 1 Sound The speed of a sound wave in a medium depends on the type of substance and whether it is a solid, liquid, or gas. Sound travels slowest in gases and fastest in solids. Sound

6 1 Sound Amplitude and Energy of Sound Waves The amount of energy a wave carries corresponds to its amplitude. More energy is transferred to the medium when the particles of the medium are forced closer together in the compressions and spread farther apart in the rarefactions.

7 1 Sound Amplitude and Energy of Sound Waves

8 1 Sound Intensity and Loudness The amount of energy transferred by a sound wave through a certain area each second is the intensity of the sound wave. Loudness is the human perception of sound intensity.

9 1 Sound Intensity and Loudness Each unit on the scale for sound intensity is called a decibel.

10 1 Sound Pitch and Frequency Pitch is the human perception of the frequency of sound waves. Frequency is a measure of how many wavelengths pass a particular point each second.

11 1 Sound Pitch and Frequency Frequency is measured in hertz (Hz). A healthy human ear can hear sound waves with frequencies from about 20 Hz to 20,000 Hz. Sound frequencies above 20,000 Hz are called ultrasonic waves. Infrasonic, or subsonic, waves have frequencies below 20 Hz.

12 1 Doppler Effect Sound The change in pitch or frequency due to the relative motion of a wave source is called the Doppler effect.

13 1 Sound A Moving Source of Sound

14 1 Sound A Moving Listener You also can hear the Doppler effect when you are moving past a sound source that is standing still. The Doppler effect happens any time the source of a sound is changing position relative to the listener.

15 1 Using Sound Sound Echolocation is the process of locating objects by emitting sounds and detecting the sound waves that reflect back. Sonar is a system that uses the reflection of underwater sound waves to detect objects. Reflected ultrasonic waves are used to examine different body parts.

16 1 Question 1 Section Check Sound frequencies above 20,000 Hz are called waves. A. infrasonic B. infrared C. subsonic D. ultrasonic

17 1 Answer Section Check The answer is D. Subsonic and infrasonic are waves with frequencies below 20 Hz.

18 1 Question 2 Section Check Describe the Doppler effect. Answer The Doppler effect is the change in pitch due to a moving wave source.

19 1 Question 3 Section Check In which of the following environments would sound waves not travel? A. at altitudes of 10,000 15,000 m B. in solid aluminum C. on the Moon D. under water

20 1 Answer Section Check The answer is C. Sound waves require a medium through which to travel. So, sound waves cannot travel through empty space.

21 2 Reflection and Refraction of Light The Interaction of Light and Matter Absorption, Transmission, and Reflection The opaque material in this candleholder only absorbs and reflects light no light passes through it.

22 2 Reflection and Refraction of Light Absorption, Transmission, and Reflection Materials that allow some light to pass through them, like the material of this candleholder are described as translucent.

23 2 Reflection and Refraction of Light Absorption, Transmission, and Reflection Transparent materials, such as this candleholder transmit almost all the light striking them, so you can see objects clearly through them.

24 2 Reflection and Refraction of Light Reflection of Light Regular and Diffuse Reflection A smooth, even surface such as a pane of glass produces a sharp image by reflecting parallel light waves in only one direction. Reflection of light waves from a smooth surface is regular reflection. To cause a regular reflection, the roughness of a surface must be less than the wavelengths it reflects.

25 2 Reflection and Refraction of Light Regular and Diffuse Reflection Reflection of light from a rough surface is diffuse reflection. Diffuse reflection is a type of scattering that occurs when light waves traveling in one direction are made to travel in many different directions.

26 2 Reflection and Refraction of Light Refraction of Light Refraction is caused by a change in the speed of a wave when it passes from one material to another.

27 2 Reflection and Refraction of Light Refraction of Light Index of refraction is the ratio of the speed of light in a vacuum to the speed of light in the material. The index of refraction indicates how much the speed of light is reduced in the material compared to its speed in empty space. The larger the index of refraction, the more light is slowed down in the material.

28 2 Reflection and Refraction of Light Refraction of Light White light, such as sunlight, is made up of light waves with range of wavelengths. Prism refracts the light twice once when it enters the prism and again when it leaves the prism.

29 2 Reflection and Refraction of Light Refraction of Light The longer wavelengths of light are slowed less and are bent the least. As a result, the different colors are separated when they emerge from the prism.

30 2 Reflection and Refraction of Light Mirages Mirages result when the air at ground level is much warmer or cooler than the air above.

31 2 Reflection and Refraction of Light Mirages The density of air increases as air cools and light waves move slower in cooler air than in warmer air. Light waves are refracted as they pass through air layers with different temperatures.

32 2 Question 1 Section Check What happens to light waves that strike an object? Answer Light waves that strike objects can be absorbed, reflected, or transmitted.

33 2 Question 2 Section Check What is the difference between refraction and reflection? Answer Refraction occurs if a light wave changes speed in moving from one material to another. Reflection occurs when light waves are returned or thrown back from a surface.

34 2 Question 3 Section Check material only absorbs and reflects light; no light passes through. A. Transparent B. Translucent C. Opaque D. Mirage

35 2 Answer Section Check The answer is C. Transparent and translucent materials both allow some light to pass through.

36 3 Mirrors, Lenses, and the Eye Light Rays Mirrors A mirror is any surface that produces a regular reflection. Plane Mirrors A flat smooth mirror is a plane mirror.

37 3 Mirrors, Lenses, and the Eye Plane Mirrors Light rays from a light source strike you. Every point that is struck by the light rays reflects these rays so they travel outward in all directions. Light rays are reflected from the mirror back to your eyes.

38 3 Mirrors, Lenses, and the Eye Virtual and Real Images Plane mirrors always form virtual images. If light rays from an object pass through the location of the image, the image is called the real image. If the surface of a mirror is curved inward, it is called a concave mirror.

39 3 Mirrors, Lenses, and the Eye Virtual and Real Images The image formed by a concave mirror depends on the location of the object relative to the focal point.

40 3 Mirrors, Lenses, and the Eye Virtual and Real Images An object between one and two focal lengths from a concave mirror is real, inverted, and larger than the object. An object closer than one focal length from a concave mirror produces a virtual image that is upright and larger than the object.

41 3 Mirrors, Lenses, and the Eye Convex Mirrors A mirror that curves outward like the back of a spoon is called a convex mirror. Reflected rays diverge and never meet, so a convex mirror forms only a virtual image. The image also is upright and smaller than the actual object is.

42 3 Lenses Mirrors, Lenses, and the Eye A lens is a transparent object with at least one curved surface that causes light rays to refract. Convex Lenses A convex lens is thicker in the middle than at the edges.

43 3 Convex Lenses Light rays are refracted toward the center of the lens. All light rays are refracted so they pass through a single point, which is the focal point of the lens. Mirrors, Lenses, and the Eye

44 3 Mirrors, Lenses, and the Eye Convex Lenses Lenses with flatter sides have longer focal lengths.

45 3 Mirrors, Lenses, and the Eye Concave Lenses A concave lens is thinner in the middle and thicker at the edges. Light rays that pass through a concave lens bend away from the optical axis.

46 3 Mirrors, Lenses, and the Eye The Human Eye Light enters your eye through a transparent covering on your eyeball called the cornea. The cornea causes light rays to bend so that they converge. Light then passes through the pupil.

47 3 Mirrors, Lenses, and the Eye The Human Eye Behind the pupil is a flexible convex lens. The retina is the inner lining of your eye, containing light sensitive cells that convert an image into electrical signals.

48 3 Mirrors, Lenses, and the Eye Brightness and Intensity The human eye can adjust to the brightness of the light that strikes it. Light intensity is the amount of light energy that strikes a certain area each second. Brightness is the human perception of light intensity. Eyes respond to bright light by decreasing the size of your pupil.

49 3 Mirrors, Lenses, and the Eye Correcting Vision Problems If you can see distant objects clearly but can t bring nearby objects into focus, then you are farsighted.

50 3 Mirrors, Lenses, and the Eye Correcting Vision Problems The eyeball might be too short or the lens isn t curved enough to form a sharp image of nearby objects on the retina.

51 3 Mirrors, Lenses, and the Eye Nearsightedness Eyes cannot form a sharp image on the retina of an object that is far away. The image is formed in front of the retina.

52 3 Question 1 Section Check A mirror curves inward. A. concave B. convex C. obtuse D. plane

53 3 Answer Section Check The answer is A. A concave mirror curves inward and forms a real image. A convex mirror curves outward and forms a virtual image.

54 3 Question 2 Section Check What type of lens refracts light rays away from the optical axis? Answer Concave lenses are thicker at the edges and refract light rays away from the optical axis.

55 3 Question 3 Section Check In nearsightedness, the image forms the retina and a lens can be used to correct it. A. behind, concave B. behind, convex C. in front of, concave D. in front of, convex

56 3 Answer Section Check The answer is C. The image forms in front of the retina and a concave lens corrects it.

57 4 Light and Color Why Objects Have Color White light is a blend of all colors of visible light. Black is the absence of visible light.

58 4 Light and Color Colored Filters A filter is a transparent material that transmits one or more colors of light but absorbs all others. The color of a filter is the color of the light that it transmits.

59 4 Seeing Color Light and Color The retina is made up of two types of cells that absorb light. A cone enables you to distinguish colors and detailed shapes of objects.

60 4 Light and Color Cones and Rods Your eyes have three types of cones. Red cones respond to mostly red and yellow light. Green cones respond to mostly yellow and green.

61 4 Light and Color Cones and Rods Blue cones respond to mostly blue and violet light. A rod is sensitive to dim light and enables you to see at night. Rod cells do not enable you to see colors.

62 4 Light and Color Color Blindness If cone cells do not function properly, you might not be able to distinguish certain colors. This condition is called color blindness. The most common form of color blindness makes it difficult to distinguish between red and green.

63 4 Mixing Colors Light and Color A pigment is a colored material that is used to change the color of other substances. Red, green, and blue are the primary colors of light. Mixing the primary colors in different proportions can produce the colors you see.

64 4 Light and Color Mixing Pigments You can make any pigment color by mixing different amounts of the three primary pigments magenta, cyan, and yellow. Pigments both absorb and reflect a range of colors.

65 4 Light and Color Mixing Pigments The area where the colors overlap appears to be black because the three blended primary pigments absorb all the primary colors of light.

66 4 Question 1 Section Check An object s color depends on the it reflects. Answer An object s color depends on the wavelengths of light it reflects. If an object absorbs all wavelengths of visible light except green, the object appears green.

67 4 Question 2 Section Check What are the two types of light-detecting cells in the eye? Answer The two types of light-detecting cells that make up the retina are the rods and cones.

68 4 Question 3 Section Check What is the appearance of the three primary colors of pigment when they are mixed? A. black B. brown C. gray D. white

69 4 Answer Section Check The answer is A. The three primary colors of pigment are magenta, cyan and yellow, and appear black when they are mixed.

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71 End of Chapter Summary File