Chapter: Sound and Light

Chapter: Sound and LightTable of Contents

Section 1: Sound

Section 2: Reflection and Refractionof Light

Section 3: Mirrors, Lenses, and the Eye

Section 4: Light and Color

• When an object vibrates, it creates sound waves.

• Sound waves are compressional waves.

SoundSound

1

• 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.

• 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.

SoundSound

1

• 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.

SoundSound

1

• 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.

Amplitude and Energy of Sound Waves

Sound

1

Amplitude and Energy of Sound Waves

Sound

1

• 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.

Intensity and LoudnessSound

1

• Each unit on the scale for sound intensity is called a decibel.

Intensity and LoudnessSound

1

• Pitch is the human perception of the frequency of sound waves.

Pitch and FrequencySound

1

• Frequency is a measure of how many wavelengths pass a particular point each second.

• Frequency is measured in hertz (Hz).Pitch and Frequency

Sound

1

• 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.

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

Doppler EffectSound

1

A Moving Source of SoundSound

1

A Moving ListenerSound

1

• 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.

Using SoundSound

1

• 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.

1Section Check

Question 1

Sound frequencies above 20,000 Hz are called __________ waves.

A. infrasonicB. infraredC. subsonicD. ultrasonic

1Section Check

The answer is D. Subsonic and infrasonic are waves with frequencies below 20 Hz.

Answer

1Section Check

Question 2

Describe the Doppler effect.

Answer

The Doppler effect is the change in pitch due to a moving wave source.

1Section Check

Question 3In which of the following environments would sound waves not travel?

A. at altitudes of 10,000 – 15,000 mB. in solid aluminumC. on the Moon D. under water

1Section Check

Answer

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

The Interaction of Light and Matter

Reflection and Refraction of Light

2

• The opaque material in this candleholder only absorbs and reflects light—no light passes through it.

Absorption, Transmission, and Reflection

• Materials that allow some light to pass through them, like the material of thiscandleholder are described as translucent.

Absorption, Transmission, and Reflection

Reflection and Refraction of Light

2

Absorption, Transmission, and Reflection

Reflection and Refraction of Light

2

• Transparent materials, such as this candleholder transmit almost all the lightstriking them, so you can see objects clearly through them.

Reflection of LightReflection and Refraction of Light

2

• A smooth, even surface such as a pane of glass produces a sharp image by reflecting parallel light waves in only one direction.

Regular and Diffuse Reflection

• 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.

Regular and Diffuse ReflectionReflection and Refraction of Light

2

• Diffuse reflection is a type of scattering that occurs when light waves traveling in one direction are made to travel in many different directions.

• Reflection of light from a rough surface is diffuse reflection.

Refraction of LightReflection and Refraction of Light

2

• Refraction is caused by a change in the speed of a wave when it passes from one material to another.

Refraction of LightReflection and Refraction of Light

2

• 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.

Refraction of LightReflection and Refraction of Light

2

• 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.

Refraction of LightReflection and Refraction of Light

2

• 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.

MiragesReflection and Refraction of Light

2

• Mirages result when the air at ground level is much warmer or cooler than the air above.

MiragesReflection and Refraction of Light

2

• 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.

2Section Check

Question 1What happens to light waves that strike an object?

AnswerLight waves that strike objects can be absorbed, reflected, or transmitted.

2Section Check

Question 2

What is the difference between refraction and reflection?

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.

Answer

2Section Check

Question 3__________ material only absorbs and reflects light; no light passes through.

A. TransparentB. TranslucentC. OpaqueD. Mirage

2Section Check

Answer

The answer is C. Transparent and translucent materials both allow some light to pass through.

• A mirror is any surface that produces a regular reflection.

• A flat smooth mirror is a plane mirror.

Light RaysMirrors, Lenses, and the Eye

3

Mirrors

Plane Mirrors

Plane MirrorsMirrors, Lenses, and the Eye

3

• 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.

• Light rays from a light source strike you.

Virtual and Real ImagesMirrors, Lenses, and the Eye

3

• 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.

• Plane mirrors always form virtual images.

Virtual and Real ImagesMirrors, Lenses, and the Eye

3

• The image formed by a concave mirror depends on the location of the object relative to the focal point.

Virtual and Real ImagesMirrors, Lenses, and the Eye

3

• 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.

Convex MirrorsMirrors, Lenses, and the Eye

3

• A mirror that curves outward like the back of a spoon is called a convex mirror.

• The image also is upright and smaller than the actual object is.

so a convex mirror forms only a virtual image.

• Reflected rays diverge and never meet,

• A lens is a transparent object with at least one curved surface that causes light rays to refract.

• A convex lens is thicker in the middle than at the edges.

LensesMirrors, Lenses, and the Eye

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.

Convex LensesMirrors, Lenses, and the Eye

3

Convex LensesMirrors, Lenses, and the Eye

3

• Lenses with flatter sides have longer focal lengths.

• 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.

Concave LensesMirrors, Lenses, and the Eye

3

• 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.

The Human EyeMirrors, Lenses, and the Eye

3

• Light then passes through the pupil.

The Human EyeMirrors, Lenses, and the Eye

3

• Behind the pupil is a flexible convex lens.

containing light sensitive cells that convert an image into electrical signals.

• The retina is the inner lining of your eye,

• 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 and IntensityMirrors, Lenses, and the Eye

3

• Brightness is the human perception of light intensity.

• Eyes respond to bright light by decreasing the size of your pupil.

• If you can see distant objects clearly but can’t bring nearby objects into focus, then you are farsighted.

Correcting Vision ProblemsMirrors, Lenses, and the Eye

3

Correcting Vision ProblemsMirrors, Lenses, and the Eye

3

• The eyeball might be too short or the lens isn’t curved enough to form a sharp image of nearby objects on the retina.

• Eyes cannot form a sharp image on the retina of an object that is far away.

NearsightednessMirrors, Lenses, and the Eye

3

• The image is formed in front of the retina.

3Section Check

Question 1

A __________ mirror curves inward.

A. concaveB. convexC. obtuseD. plane

3Section 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.

Answer

3Section Check

Question 2What type of lens refracts light rays away from the optical axis?

AnswerConcave lenses are thicker at the edges and refract light rays away from the optical axis.

3Section Check

Question 3In nearsightedness, the image forms _______ the retina and a _______ lens can be used to correct it.

A. behind, concaveB. behind, convexC. in front of, concaveD. in front of, convex

3Section Check

Answer

The answer is C. The image forms in front of the retina and a concave lens corrects it.

Why Objects Have Color Light and Color

4

• White light is a blend of all colors of visible light.

• Black is the absence of visible light.

Colored Filters Light and Color

4

• 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.

Seeing ColorLight and Color

4

• 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.

Cones and RodsLight and Color

4

• Your eyes have three types of cones.

• Red cones respond to mostly red and yellow light.

• Green cones respond to mostly yellow and green.

Cones and RodsLight and Color

4

• 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.

Color BlindnessLight and Color

4

• 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.

Mixing ColorsLight and Color

4

• 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.

Mixing PigmentsLight and Color

4

• 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.

Mixing PigmentsLight and Color

4

• The area where the colors overlap appears to be black because the three blended primary pigments absorb all the primary colors of light.

4Section Check

Question 1An object’s color depends on the __________ it reflects.

AnswerAn 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.

4Section Check

Question 2

What are the two types of light-detecting cells in the eye?

The two types of light-detecting cells that make up the retina are the rods and cones.

Answer

4Section Check

Question 3What is the appearance of the three primary colors of pigment when they are mixed?

A. blackB. brownC. grayD. white

4Section Check

Answer

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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