Physics Chapter 26 Properties of Light: Terms, Homework, Practice Test and Test

Flashcard maker : Lily Taylor
Electromagnetic Wave
An energy carrying wave emitted by a vibrating change (often electrons) that is composed of oscillating electric and magnetic fields that regenerate one another
Electromagnetic Spectrum
The range of electromagnetic waves extending in frequency from radio waves to gamma rays
Transparent
The property of materials to pass light in straight lines without being scattered
Opaque
The property of materials not to allow passage of light (opposite of transparent).
Shadow
A shaded region that appears where light rays are blocked by an object
Umbra
The darker part of a shadow where all the light is blocked
Penumbra
A partial shadow that appears where some but not all of the light is blocked
Solar Eclipse
An event in which the Moon blocks light from the Sun and the Moon’s shadow falls on part of Earth
Lunar Eclipse
An event in which the Moon passes into the shadow of Earth
Light is the only thing we can see
Electromagnetic Waves
Originates from the accelerated motion of electrons
Electromagnetic Waves
Electromagnetic phenomenon
Electromagnetic Waves
Made up of vibrating electric and magnetic fields
Electromagnetic Waves
Classification of electromagnetic waves according to frequency
Electromagnetic Spectrum
Lowest frequency of light we can see appears red
Electromagnetic Spectrum
Highest frequency of light we can see appears violet
Electromagnetic Spectrum
Higher frequency of light is ultraviolet more energetic and causes sunburns
Electromagnetic Spectrum
Beyond are X-ray and gamma ray
Electromagnetic Spectrum
No sharp boundary between regions
Electromagnetic Spectrum
The electromagnetic spectrum spans waves ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of
Visible light
Which of these is fundamentally different from the other sound waves, light waves, radio waves, or x-rays
Sound waves
Vibrations due to a vibrating source
Transparent Materials and Sound
How light penetrates material such as glass
Transparent Materials
Electrons or molecules in the glass are forced into vibration
Transparent Materials
Energy is momentarily absorbed and vibrates the electrons in the glass
Transparent Materials
Vibrating electron either emits a photon or transfers the energy as heat
Transparent Materials
Time delay between absorption and re-emission of energy of vibrating electrons results in a lower average speed of light through a
Transparent Material
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
Transparent Material
Glass is ____ to visible light
transparent
Strictly speaking, the photons of light incident on glass are
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

Compared with the frequency of illuminating light on a sheet of transparent plastic, the frequency of light that is transmitted
is the same

Note: Speed of light in plastic may vary, but the frequency transmitted doesn’t

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

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