Section 1: Sound

• Sound Waves

  • When an object vibrates it creates sound waves

  • A vibrating tuning fork produces compressions and rarefactions that travel outward from the tuning fork. These compressions and rarefactions form a sound wave.

• The Speed of Sound

  • A sound wave moves in air as collisions between the molecules in air transfer energy from place to place.

  • The material in which a sound wave moves is called a medium.

  • Sound waves cannot travel in empty space where there are no particles.

  • The speed of a sound wave in a medium depends on the type of substance and whether it is a solid, liquid, or gas.

  • The speed of sound waves also depends on the temperature of the medium

    • As the temperature of a substance increases, its atoms and molecules move faster

• Amplitude and Energy of Sound Waves

  • A vibrating object makes a wave by transferring energy to the medium.

    • 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.

  • The amplitude of a sound wave depends on the density of the particles in the compressions and rarefactions.

  • In a high-amplitude sound wave, particles are tightly packed in the compressions and far apart in the rarefactions.

  • In a low-amplitude sound wave, particles are less tightly packed in the compressions and not as far apart in the rarefactions.

• Intensity and Loudness

  • The intensity of a sound wave decreases as the wave spreads out from the source of the sound. The energy of the wave is spread over a larger area as the wave spreads out.

    • Intensity: The amount of energy transferred by a sound wave through a certain area each second

  • When you hear different sounds, you do not need special equipment to know which sounds have greater intensity.

    • Loudness: the human perception of sound intensity.

    • As the intensity of a sound wave increases, the loudness of the sound also increases.

  • Decibel: Each unit on the scale for sound intensity

  • Sounds with intensity levels above 120 dB may cause pain and permanent hearing loss.

• Pitch and Frequency

  • Every note has a different frequency, which gives it a distinct pitch.

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

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

    • For a compressional wave, such as sound, the frequency is the number of compressions or the number of rarefactions that pass by each second.

    • A healthy human ear can hear sound waves with frequencies from about 20 Hz to 20,000 Hz.

  • Infrasonic, or subsonic, waves have frequencies below 20 Hz—too low for most people to hear.

    • These waves are produced by sources that vibrate slowly, such as wind, heavy machinery, and earthquakes.

    • Although you can’t hear infrasonic waves, you might feel them as a rumble inside your body.

• The Doppler Effect: The change in pitch or frequency due to the relative motion of a wave source

  • The Doppler effect occurs when the source of a sound wave is moving relative to a listener.

    • You also can hear the Doppler effect when you are moving past a sound source that is standing still.

    • The faster the change in position, the greater the change in frequency and pitch.

• Using Sound

  • When sound waves strike an object, they can be absorbed by the object, transmitted through the object, or reflected from the object.

  • By detecting the sound waves reflected from an object, the size, shape, and location of an object can be determined.

  • 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.

  • Using special instruments, medical professionals can send ultrasonic waves into a specific part of a patient’s body.

    • Ultrasonic waves are directed into a pregnant woman’s uterus to form images of her fetus.

    • High-frequency sound waves can be used to treat certain medical problems.

Section 2: Reflection and Refraction of Light

• The Interaction of Light and Matter

  • What you see depends on the amount of light in the room and the color of the objects. For you to see an object, it must reflect or emit some light that reaches your eyes.

  • Objects can absorb light, reflect light, and transmit light—allow light to pass through them.'

  • Opaque: only absorbs and reflects light—no light passes through it.

  • Translucent: allow some light to pass through them

  • Transparent: transmit almost all the light striking them

• Reflection of Light

  • According to the law of reflection, light is reflected so that the angle of incidence always equals the angle of 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 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.

    • Scattering also occurs when light waves traveling through the air reflect off small particles.

• Refraction of Light

  • The amount of bending that takes place depends on the speeds of light in both materials.

  • The greater the change in speed, the more the light will be bent as it passes at an angle from one material to the other.

  • Index of Refraction: the ratio of the speed of light in a vacuum to the speed of light in the material.

    • The larger the index of refraction, the more light is slowed down in the material.

    • The index of refraction is usually largest for solids and smallest for gases.

  • The spectrum of colors is produced because the speed of light in a material also depends on the wavelength of the light.

    • Refraction causes a prism to separate a beam of white light into different colors.

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

    • Mirages result when air near the ground is much warmer or cooler than the air above. This causes light waves reflected from an object to refract, creating one or more additional images.

    • The density of air increases as air cools and light waves move slower in cooler air than in warmer air.

Section 3: Mirrors, Lenses, and the Eye

• Light Rays

  • Light sources send out light waves in all directions.

  • These waves spread out like ripples on the surface of water spread out from the point of impact of a pebble

  • Each narrow light beam is called a light ray.

• Mirrors

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

  • Mirrors can be flat, curved inward, or curved outward.

  • Plane Mirror: A flat, smooth mirror

    • Seeing an image of yourself in a mirror involves two sets of reflections: light rays are reflected from you and then are reflected by the mirror.

    • Every point that is struck by the light rays reflects these rays so they travel out- ward in all directions.

  • Your brain interprets the light rays reflected by the mirror as coming from a point behind the mirror.

    • If light rays from an object pass through the location of the image, the image is called a real image.

    • Rays that enter your eyes seem to come from behind the mirror. This makes the image seem to be behind the mirror. However, no light rays actually pass through the place where the image seems to be located. This type of image is called a virtual image.

  • Concave Mirror: If the surface of a mirror is curved inward

    • The optical axis is an imaginary straight line drawn perpendicular to the surface of the mirror at its center

    • The distance from the center of the mirror to the focal point is called the focal length.

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

  • When an object is between one and two focal lengths from a concave mirror, the image 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.

    • No image is produced if the object is located at the focal point.

  • Convex Mirror: A mirror that curves outward like the back of a spoon

    • A convex mirror forms a reduced, upright, virtual image.

    • The 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.

• Lenses

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

  • The image that a lens forms depends on the shape of the lens. Like curved mirrors, lenses can be convex or concave.

  • Convex Lens: thicker in the middle than at the edges.

    • Light rays that are parallel to the optical axis are refracted so that they pass through the focal point. A light ray that passes through the center of the lens is not refracted.

    • The less curved the sides of the lens, the less light rays are bent. As a result, lenses with flatter sides have longer focal lengths.

  • Concave Lens: thinner in the middle and thicker at the edges.

    • A concave lens refracts light rays so they spread out away from the optical axis.

    • Concave lenses are used in some types of eyeglasses and some telescopes

• The Human Eye

  • The cornea and lens in your eye bend light rays so that a sharp image is formed on the retina.

  • The retina is the inner lining of your eye.

    • The retina contains light-sensitive cells that convert an image into electrical signals.

    • These signals then are carried along the optic nerve to your brain to be interpreted.

  • 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

  • Intensity depends on your distance from a light source.

• Correcting Vision Problems

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

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

    • Convex lenses can be used to bend incoming light rays so they converge before they enter the eye.

  • When you are nearsighted you can only see nearby objects clearly

    • To correct this problem, a nearsighted person can wear concave lenses.

    • A concave lens causes incoming light rays from distant objects to diverge before they reach the eye. Then the rays can be focused by the eye to form a sharp image on the retina.

Section 4: Light and Color

• Why Objects Have Color

  • An object’s color depends on the wavelengths of light it reflects.

  • Although some objects appear to be black, black isn’t a color.

    • Black is the absence of visible light. Objects that appear black absorb all colors of light and reflect little or no light back to your eyes.

  • Wearing tinted glasses changes the color of almost everything you see.

    • 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 Color

  • In a healthy eye, light enters the eye through the cornea, is focused by the lens, and finally forms an image on the retina.

  • Light enters the eye and focuses on the retina. The two types of light-detecting cells that make up the retina are called rods and cones.

    • One type of cell in the retina, called a cone, enables you to distinguish colors and detailed shapes of objects.

      • Cones need bright light to generate nerve impulses, so they do not operate in dim light

  • Your eyes have three types of cones, each of which responds to a different range of wavelengths.

    • Red cones respond to mostly red and yellow light.

    • Green cones respond to mostly yellow and green light.

    • Blue cones respond to mostly blue and violet light.

  • The second type of cell in the retina, called a rod, is sensitive to dim light and enables you to see at night.

  • Color blindness is an inherited sex-linked condition in

    which certain sets of cones in the retina do not function properly.

    • If one or more of your sets of cone cells do not function properly, you might not be able to distinguish certain colors.

    • About eight percent of men and one-half percent of women have some form of color blindness.

• Mixing Colors

  • Pigment: a colored material that is used to change the color of other substances.

    • The color of a pigment results from the different wavelengths of light that the pigment reflects.

  • Red, green, and blue—are the primary colors of light

    • They correspond to the three different types of cones in the retina of your eye.

    • White light is produced when the three primary colors of light are mixed in equal amounts.

  • Paints are made with pigments.

    • Pigments produce color as a result of the wavelengths of light they reflect.

  • You can make any pigment color by mixing different amounts of the three primary pigments—magenta (bluish red), cyan (greenish blue), and yellow.

    • A primary pigment’s color depends on the wavelengths of the light that it reflects.

    • When the primary pigment colors are combined, they absorb all wavelengths of visible light and produce black.

    • Because black results from the absence of reflected light, the primary pigments are called subtractive colors.