Physics Chapter 26 Properties of Light: Terms, Homework, Practice Test and Test – Flashcards
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Electromagnetic Wave
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An energy carrying wave emitted by a vibrating change (often electrons) that is composed of oscillating electric and magnetic fields that regenerate one another
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Electromagnetic Spectrum
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The range of electromagnetic waves extending in frequency from radio waves to gamma rays
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Transparent
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The property of materials to pass light in straight lines without being scattered
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Opaque
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The property of materials not to allow passage of light (opposite of transparent).
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Shadow
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A shaded region that appears where light rays are blocked by an object
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Umbra
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The darker part of a shadow where all the light is blocked
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Penumbra
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A partial shadow that appears where some but not all of the light is blocked
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Solar Eclipse
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An event in which the Moon blocks light from the Sun and the Moon's shadow falls on part of Earth
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Lunar Eclipse
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An event in which the Moon passes into the shadow of Earth
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Light is the only thing we can see
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Electromagnetic Waves
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Originates from the accelerated motion of electrons
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Electromagnetic Waves
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Electromagnetic phenomenon
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Electromagnetic Waves
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Made up of vibrating electric and magnetic fields
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Electromagnetic Waves
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Classification of electromagnetic waves according to frequency
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Electromagnetic Spectrum
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Lowest frequency of light we can see appears red
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Electromagnetic Spectrum
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Highest frequency of light we can see appears violet
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Electromagnetic Spectrum
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Higher frequency of light is ultraviolet more energetic and causes sunburns
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Electromagnetic Spectrum
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Beyond are X-ray and gamma ray
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Electromagnetic Spectrum
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No sharp boundary between regions
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Electromagnetic Spectrum
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The electromagnetic spectrum spans waves ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of
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Visible light
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Which of these is fundamentally different from the other sound waves, light waves, radio waves, or x-rays
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Sound waves
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Vibrations due to a vibrating source
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Transparent Materials and Sound
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How light penetrates material such as glass
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Transparent Materials
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Electrons or molecules in the glass are forced into vibration
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Transparent Materials
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Energy is momentarily absorbed and vibrates the electrons in the glass
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Transparent Materials
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Vibrating electron either emits a photon or transfers the energy as heat
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Transparent Materials
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Time delay between absorption and re-emission of energy of vibrating electrons results in a lower average speed of light through a
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Transparent Material
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In glass, infrared waves, with frequencies lower than those of visible light, cause not only the electrons but entire atoms or molecules to vibrate, increasing the temperature of the structure
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Transparent Material
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Glass is ____ to visible light
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transparent
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Strictly speaking, the photons of light incident on glass are
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not the ones that travel through and exit the other side. Note: The light that exits the glass is not the same light that begins the process of absorption and re-emission
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Compared with the frequency of illuminating light on a sheet of transparent plastic, the frequency of light that is transmitted
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is the same Note: Speed of light in plastic may vary, but the frequency transmitted doesn't
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The average speed of light is less in
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glass
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Absorbtion of light without re-mitting it
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Opaque
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Vibration given by light to their atoms and molecules are turned into random kinetic energy- into internal energy
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Opaque
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Light shining on metal forces free electrons in the metal into vibrations that emit their own light as reflection
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Opaque Materials
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Light incident on dry surfaces bounces directly to your eye
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Opaque Materials
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Light incident on wet surfaces bounces inside the transparent wet region, absorbing energy with each bounce, and reaches your eye darker than from a dry surface
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Opaque Materials
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A thin beam of light is often called a ray
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Shadows
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When we stand in the sunlight, some of the light is stopped while other rays continue in a straight line path
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Shadows (Opaque Material)
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A region where light rays do not reach
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Shadow ( Opaque Material)
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A large, far-away light source or a small, nearby light source will produce a
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Sharp Shadow
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A large, nearby light source produces a
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blurry shadow
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A total shadow is called
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Umbra
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A partial shadow is called
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Penumbra
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Appears where some of the light is blocked but where other light fills it in
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Penumbra
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Occurs where light from a broad source is only partially blocked
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Penumbra
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The large size of the Sun, the rays taper to provide an umbra(total eclipse) and a surrounding penumbra (partial eclipse)
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Solar Eclipse
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The Moon passes completely into the shadow of Earth
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Lunar Eclipse
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As light enters the eye, it moves through the transparent cover called
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cornea
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Cornea does about 70% of the bending of the light before it passes through an opening in the
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Iris (colored part of the eye)
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The opening of the eye is called
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pupil
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In a vacuum all electromagnetic waves move at the same speed
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and differ from one another in their frequency
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What does a changing magnetic field induce
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a changing electric field
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What does a changing electric field induce
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a changing magnetic field
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What produces an electromagnetic wave
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an oscillating or accelerating electric change
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The electromagnetic waves having the highest speed in free space are
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none in particular as gamma, radio, and light have the same speed
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Materials that clearly transmit visible light are said to be
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transparent
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How does the frequency of reemitted light in a transparent material compare with the frequency of the light that stimulates its reemission
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they are the same
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The part of the eye that enables us to see colors is the
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cones in the retina
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Why are metals shiny
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Free electrons in metals vibrate when light strikes them, thereby reemitting the light as reflected light
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Why do wet objects normally look darker than the same objects when dry
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Light bounces around inside the transparent water region covering a wet object, getting absorbed more on each bounce
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Your friend says that any radio wave travels appreciably faster than any sound wave
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agree with your friend unconditionally
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Which of these electromagnetic waves have the shortest wavelength
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x-rays
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If the color spectrum ranges from red to violet, then it ranges from
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both: long wavelengths to short wavelengths and low frequencies to high frequencies.
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A main difference between a radio wave and a light wave is
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wavelength and frequency
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Which of the following cannot travel in a vacuum
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sound wave
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Compared to its average speed in air, the average speed of a beam of light in glass is
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less
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Colors are barely seen or not at all in nighttime because moonlight
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is too dim to activate the retina's cones
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When a red rose is held in white light, the color of its petals appears
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red
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What color light is transmitted through a piece of red glass
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Red
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On million ___lies in the middle of Am radio band
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MHz
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The very high frequency VHF is
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television band waves and FM radio waves
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Why are red, green, and blue called the additive primary colors
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Adding appropriate amounts of red plus green plus blue lights can produce almost any color of the spectrum
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Different colors of light correspond to different light
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frequencies
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Most of the waves in the electromagnetic spectrum are
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Invisible
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Electromagnetic waves consist of
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oscillating electric and magnetic fields
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The source of all electromagnetic waves is
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accelerating electric charges
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A changing electric field induces a changing
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magnetic field
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If a light signal and a radio signal were emitted simultaneously from Alpha Centauri, the first to reach Earth would be the
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both at the same time
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Which of these electromagnetic waves have the longest wavelength
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radio waves
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Compared to ultraviolet waves, the wavelength of infrared waves is
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longer
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Compared to ultraviolet waves, the frequency of infrared waves is
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lower
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A main difference between a radio wave and a sound wave is
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medium or no medium
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Metals are shiny because
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their electrons vibrate to the oscillations of any incident light
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Materials generally become warmer when light is
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absorbed by them
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Sunburns are produced by
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ultraviolet light
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Which best shields you from sunburn when at the beach
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a sheet of glass between you and the Sun
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The cones in the retina of the eye are
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most densely packed at the center of vision
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The main difference between the retina of a human eye and that of a dog's eye is the
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absence of cones in a dog's retina
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In free space, electromagnetic waves travel at a
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single speed
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The sensation of color is seen when light falls on the eye's
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cones
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Materials that do not transmit visible light are said to be
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opaque
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What do electric and magnetic fields contain and transport
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energy
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The smallest portion of the electromagnetic spectrum is
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visible light
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Electromagnetic waves are composed of
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electric and magnetic fields
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Compared to radio waves, the velocity of visible light waves in a vacuum is
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the same
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Why are infrared waves often called heat waves
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Infrared light vibrates entire atoms and molecules, and this vibration increases the temperature of the absorbing substance
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Radio waves travel
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always much faster than sound waves
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How does the average speed of light in glass compare with its speed in a vacuum
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The average speed of light in glass is about 67% of the speed of light in a vacuum
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The fact that light travels only at 300,000 km/s in free space is a consequence of
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energy conservation
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What is the wavelength of an electromagnetic wave that has a frequency of 3 kilohertz
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more than 1km
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What are the principal differences between a radio wave and light? Between light and an X-ray
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Radio waves have a lower frequency and longer wavelength than visible light waves. Light waves have a lower frequency and longer wavelength than X-rays.
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What is the frequency of an electromagnetic wave that has a wavelength of 300,000 km
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1 Hz
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The sound coming from one tuning fork can force another to vibrate. What is the analogous effect for light?
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The light emitted by resonant vibrations of an electron around one atom can be absorbed by an electron with the same resonant frequency of vibration in another atom.
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What is the fate of the energy in ultraviolet light that is incident upon glass
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Ultraviolet light will be absorbed by the resonant vibration of electrons and turned into internal energy and a temperature increase
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How do the rods in the eye differ from the cones
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The rods are rod-shaped and are more sensitive to dim light. The cones are cone-shaped and are color-sensitive.
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Why do opaque materials become warmer when light shines on them
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Vibrations given by the light to their electrons, atoms, and molecules that absorb the light become internal energy, thus leading to a temperature increase.
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What is the fate of the energy in visible light that is incident upon clear glass
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Visible light will be transmitted by the glass, losing little energy in the process, so the energy remains visible light energy
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What is the fate of the energy in infrared light incident on glass
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Infrared light will make atoms vibrate, thus becoming internal energy and a temperature increase.
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How is the wavelength of light related to its frequency
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The wavelength is inversely proportional to the frequency
