Exam 3
light speed through diamond
.41C
light speed through glass
.67C
light speed through water
.75C
A certain radar installation tracks airplanes by transmitting electromagnetic radiation of wavelength 2.6cm. Find the frequency.
1.2 x 10^10 Hz C=λf f=C/λ 3 x 10^8 m/s / 2.6 cm 2.6 cm = .026 m f= 3 x 10^8 m/s / .026 m 1.153546154 x 10^10 1/s two significant figures: 1.2 x 10^10 Hz or 12 GHz
light speed through air
1C
speed of light
3.00 x 10^8 m/s 300,000 km/s
Find the time required for a pulse of radar waves to reach an airplane 5.8 km away and return.
3.9 x 10^-5 s s=d/t t=d/s d: 5.8 x 2 (roundtrip)=11.6 km 11.6 km= 11600 m or 1.16 x 10^4 m t= 1.16 x 10^4 m / 3 x 10^8 m/s t=3.866666667 x 10^-5 s two significant figures: 3.9 x 10^-5
What is the wavelength of a wave that has a frequency of 1 Hz and travels at 300,000 km/s?
300,000 km 300,000 km/s X 1Hz(oscillation per second) = 300,000 km pg. 490
violet light
400 nm, shortest wavelength
range of visible light
400nm-700nm
red light
700 nm, longest wavelength
light is always oscillating between electric and magnetic field at what angle?
90 degrees
doppler effect
A change in sound frequency caused by motion of the sound source, motion of the listener, or both.
What does a changing *magnetic* field induce?
A changing *electric* field. "If lights were to slow down, its changing electric field would generate a weaker magnetic field, which, in turn, would generate a weaker electric field, and so on, until the wave died out."
What does a changing *electric* field induce?
A changing *magnetic* field. "If light were to speed up, the changing electric field would generate a stronger magnetic field, which in turn would generate a stronger electric field, etc."
Which warms more quickly in sunlight - a colorless or a colored piece of glass? Why?
A colored piece of glass warms quickest because it absorbs more frequencies of light, thus converting the energy to temperature.
infrared heat
A form of radiation created when the heat from a source is absorbed by another material and radiated outward to heat another object
Why does a high-flying airplane cast little or no shadow on the ground below while a low-flying airplane casts a sharp shadow?
A high flying airplane is farther away from a surface (ground), thus the shadow is less distinct or nonevident as the penumbra expands into a big blur. A low flying airplane casts a sharp shadow since it is near the ground surface, with light coming from slightly different directions not spreading out much below it. (a larger umbra)
Why does the sky normally appear blue?
Air molecules have resonances in the ultraviolet, so they scatter blue light more than red light.
What type of electromagnetic radiation travels with the highest speed?
All types of electromagnetic radiation travel at the same speed, regardless of wavelength. The speed of light is the same for all types of electromagnetic radiation (not just visible light).
What produces an electromagnetic wave?
An oscillating or accelerating electric charge. "The vibrating electric and magnetic fields regenerate each other to make up an *electromagnetic wave* which emanates from the vibrating charge."
During a solar eclipse, who can observe the total eclipse?
Anyone living where the penumbra sweeps by. Only people lucky enough to be in the small umbra can witness a total solar eclipse.
Hydrogen Absorption Spectrum
Black lines indicate the wavelengths of light that are absorbed
How can you make magenta using red, green, and blue light projectors?
Blue and red light combined
Why is the sky blue?
Blue light is scattered by the atmosphere more than other colors.
speed of light equation
C=λf, where λ is the wavelength of a photon, f is the frequency of a photon, and C=3.00*10^8
Gamma ray sources
Cobalt-60 and Cesium-137 some neutron stars and black hole accretion disks
ROYGBIV
Colors of the visible spectrum in order of wavelength and frequency red, orange, yellow, green, blue, indigo, violet
Why does the color of sunsets vary from day to day?
Different particles in the air each day scatter and absorb different wavelengths of light, thus giving the sky many different colors.
energy and wavelength equation
E=hc/λ E: energy (variable) h: plank's constant (constant) c:speed of light 3x10^8 (constant) λ=wavelength (variable)
energy of light equation
E=hf E= energy of photon h=plank's constant f=frequency
What do electric and magnetic fields contain and transport?
Energy. "Electric and magnetic fiends remain in perfect balance, reinforcing each other as they carry energy through space." pg.488
True or False: Every time the Moon Is in the "New" phase (when it is essentially between the Earth and the Sun), its shadow touches some portion of the Earth.
False Often, when the Moon is in the "New" phase, it is below or above the ecliptic, so its shadow misses the Earth completely. This is why we don't have lunar eclipses every month.
Why are metals shiny?
Free electrons in metals vibrate when light strikes them, thereby reemitting the light as reflected light.
Which has highest frequency? Gamma rays, xrays, ultraviolet, visible, infrared, microwave, radio
Gamma rays
Rank electromagnetic spectrum from highest to lowest frequency
Gamma rays, x-rays, ultraviolet, visible light, infrared, microwave, radio
Rank the electromagnetic spectrum from shortest to longest wavelength
Gamma rays, x-rays, ultraviolet, visible light, infrared, microwave, radio
How can you make yellow using red, green, and blue light projectors?
Green light and red light combined
x-ray sources
High voltage x-Ray tubes, stars and galaxies
How is the fact that an electromagnetic wave in space never slows down consistent with the law of conservation of energy?
If light slowed down, its energy would decrease, thereby violating the law of conservation of energy. "There is only one speed for which electric and magnetic fields remain in perfect balance... carrying energy forward without loss or gain." "Energy would be lost and none would be transported form one place to another. So light cannot travel slower than it does."
How is the fact that an electromagnetic wave in space never speeds up consistent with the law of conservation of energy?
If light speeded up, its energy would increase, thereby violating the law of conservation of energy. "The changing electric field would generate a stronger magnetic field; a crescendo of ever-increasing field strength and energy," a violation! In a vacuum, all electromagnetic waves move at the same speed and differ from one another in their frequency.
What part of the electromagnetic spectrum is most absorbed by water?
Infrared
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.
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. "Frequencies lower than those of visible light cause entire atoms or molecules to vibrate, increasing internal energy and temp." *heat waves
About how much of the measured electromagnetic spectrum does light occupy?
Less than 1 millionth of 1%, a tiny fraction of the spectrum! Lowest frequency of light visible to us is red, with highest of violet. *roygbiv
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. Incident light on dry surfaces bounce directly to your eye.
What is the color of visible light of the lowest frequencies? Of the highest frequencies?
Lowest frequency of light visible to us is red, with highest of violet. *roygbiv
Distinguish between an umbra and a penumbra.
No light from the source enters the shadow in an umbra, while some, but not all, light from the source enters the penumbra.
Why is the sunset red?
Only the low-frequency red light penetrates the thick layers of atmosphere when the Sun is low in the sky.
What do we mean when we say that outer space isn't really empty?
Outer space is filled with electromagnetic waves. Therefore, it's not empty.
non-ionizing radiation
Radiation that has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons
What type of electromagnetic wave has a wavelength roughly equal to the height of a person?
Radio waves All electromagnetic waves with a wavelength longer than 10-4 meters is considered radio waves.
What are the principal differences between a radio wave and visible light?
Radio waves have a lower frequency and longer wavelength than visible light waves.
Which have the longest wavelengths? a). Light waves b). X-rays c). Radio waves
Radio waves have the longest wavelengths (and lowest frequency) of the 3
What is the color of visible light with the lowest frequency?
Red
Blue, green, and red light projectors are all shining on a screen, producing a white spot. A spider comes down in front of the red projector, but isn't blocking the other two projectors. What color is the "shadow" of the spider?
Since it is blocking red light, only green and blue are in the "shadow," forming turquoise.
Only some of the people on the daytime side of Earth can witness a solar eclipse when it occurs, whereas all the people on the nighttime side of Earth can witness a lunar eclipse when it occurs. Why is this so?
Since the shadow of the relatively small moon on the large Earth covers a very small part of Earth's surface, only relatively few people are in the shadow of the moon during a solar eclipse.But the shadow of Earth that covers the moon during a lunar eclipse is in view of everybody who can see the moon in the nighttime sky.Sun>>moon>>Earth = small shadow (Solar)Sun>>Earth>>moon = large shadow (Lunar)
What is the wavelength of a wave that has a frequency of 1Hz & travels at 300,000 km/s?
Since the speed of the wave is 300,000 km/s, an electric charge oscillating once per second (1Hz) will produce a wave with a wavelength of 300,000 Km. This is because only one wavelength is created in one second. Equation is 300,000 km/s *divided by* 1Hz *If frequency of oscillation was 10Hz, then 10 waves would be produced every (1s), & wavelength would be 30,000Km* Equation then would be 300,000 km/s *divided by* 10Hz
Which particles interact more with high-frequency light?
Small particles
The nearest star beyond the sun is Alpha Centauri, about 4.2x10^16m away. IF we were to receive a radio signal from this far today, show that the message would have been sent 4.4 year ago
T=D/V T= time (4.4 years) D= Distance (4.2x10^16) V= Speed of radio waves (3 x 108 m/s) = 1.4x10^8 *Convert to years*: 1.4x10^8 x 1hr/36000s x 1day/24hrs x 1year/365 days = *4.4 years*
A helium-neon laser emits a light of 633nm in wavelength. Light from an argon laser emits a wavelength of 515nm. Which laser emits a higher frequency light?
The argon laser emits a higher frequency light (due to its shorter wavelengths)
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. Speed of light in a vacuum is constant 300,000 km/s. (*c*) In glass, speed is 0.67*c* In water, speed is 0.75*c* In diamond, speed is 0.41*c*
What is the effect on the color of a cloud when it contains an abundance of large droplets?
The cloud becomes dark.
You can get a sunburn on a cloudy day, but you can't get a sunburn even on a sunny day if you are behind glass. Explain.
The clouds allow UV light to pass through, but glass does not allow UV light to pass through. Glass only lets in visible light.
What is it exactly that waves in a light-wave?
The electric and Magnetic fields
How does the frequency of radio waves compare to the frequency of the vibrating electrons that produce it?
The frequency of a wave is the same as the frequency of the vibrating source that creates it
The intensity of light decreases as the inverse square of the distance from the source. Does this mean that light energy is lost? Explain.
The frequency of reemitted light is identical to the frequency of incidental light. At this speed, energy is carried forward withouth loss or gain. There is a time delay between absorption and reemission. It is this time delay that results in a lower average speed of light through a transparent material.
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. "Vibrations in the emitter are transmitted to vibrations in the receiver."
Why does the Sun look reddish at sunrise and sunset but not at noon?
The longer path length of sunlight at sunrise and sunset scatters out more blue light.
optically dense
The measure of transmittance of an optical medium for a given wavelength
Why is the sky blue when the Sun is overhead?
The molecules in the atmosphere scatter blue light more than any other light, so the sky looks blue.
What happens when light from the Sun interacts with the molecules of the atmosphere?
The molecules scatter the light.
How do the rods in the eye differ from the cones?
The rods are rod-shaped and are more sensitive to dim light; cluster in periphery. The cones are cone-shaped and are color-sensitive; cluster near fovea
How does the speed of radio waves compare with the speed of gamma rays?
The speed of radio waves is equal to the speed of gamma rays
What do we mean when we say that outer space is not really empty?
The vacuum of space is full of electromagnetic wave energy. "Montages of electromagnetic waves permeate every part of our surroundings; some are visible are light. Radio waves, free electrons, radiation is everywhere."
How is the wavelength of light related to its frequency?
The wavelength is inversely proportional to the frequency. "waves of low frequency have long wavelengths, and waves of high frequencies have short wavelengths."
How do the wavelength and frequency of infrared light compare to the wavelength of ultraviolet light?
The wavelength of infrared is larger that ultraviolet, and the frequency is smaller.
How does the frequency of a radio wave compare to the frequency of the vibrating electrons that produce it?
They are the same. "The frequency of a wave is the same as the frequency of the vibrating source that creates the wave." "The frequency of an electromagnetic wave as it vibrates through space is identical to the frequency of the oscillating electric charge that generates it."
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 frequency of the reemitted light is identical to the frequency of the incident light. However, slight time delay lowers average speed of light through a transparent material."
How does the speed of light that emerges from a pane of glass compare with the speed of light incident on the glass?
They are the same. The incident light is at speed *c* Through the glass, speed is 0.67*c* The emergent light is at speed *c* again.
In what region of the electromagnetic spectrum is the resonant frequency of electrons in glass?
UV "UV shines on glass, resonance occurs and electrons vibrate to large amplitudes. Energy received by glass atoms is either reemitted or passed onto neighbor atoms by collision. Glass is not transparent to UV light."
Which has shorter wavelengths? Highest frequency? a). Ultraviolet light b). Infrared light
Ultraviolet light has the shortest wavelength and highest frequency
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. "Resonating atoms in glass hold onto UV light energy for a long time, and give up energy as heat."
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. "They absorb light without reemitting it. Vibrations turn into random kinetic energy."
Which type of visible light has the highest frequency?
Violet Violet light has a frequency almost twice as much as that of red light.
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. "Glass is transparent to all frequencies of visible light, passing on reemitted light of same frequency as the incident light."
What accounts for the whiteness of a cloud?
Water droplets of different sizes scatter a variety of light frequencies, resulting in a white cloud.
When are objects on the periphery of your vision most noticeable?
When they are moving. "The periphery is very sensitive to motion. We are wired to look for movement to the side of our visual field."
What is the evidence for the statement that white light is a composite of all the colors of the spectrum?
White light can be separated into all colors of the spectrum using a prism, and then these colors can be recombined to make white light.
To what color of light are our eyes most sensitive?
Yellow-green
What is the color of the peak frequency of solar radiation when it is plotted versus wavelength?
Yellow-green
Do Earth and the Moon always cast shadows? What do we call the occurrence where one passes within the shadow of the other?
Yes, they both cast shadows. When one passes into the shadow of the other, there is an eclipse. Solar: Earth passes in Moon's shadow Lunar: Moon passes in Earth's shadow
When you look at a distant galaxy through a telescope, how is it that you're looking backward in time?
You are seeing the delay for the light to reach your eye.
index of refraction
a measure of the amount a ray of light bends when it passes from one medium to another
Plank's constant
a number used to calculate the radiant energy (E) absorbed or emitted by a body based on the frequency of radiation
photon
a particle of light
light
a propagating, oscillating electric field & magnetic field
opaque materials
absorb light without re-emitting it
A light wave is caused by
accelerating charged particles.
Examples of transparent materials
air, water, glass, diamonds
rank index of refraction least to most for the following materials: air, water, glass, diamonds
air, water, glass, diamonds
rank optical density from least to most for the following materials: air, water, glass, diamonds
air, water, glass, diamonds
transparent materials
allow light to pass through can see through them
What gives off infrared light?
any object in the universe that has density (mass & volume)
Which has the higher frequency, red light or blue light?
blue light
Is the atmosphere near the earth hotter or colder than the upper atmosphere?
colder due to upper atmosphere absorbing majority of light waves
What color results when red is subtracted from white light?
cyan
Light can appear to slowdown depending on the ___________ of the matter it is traveling through.
density
energy of light and frequency relationship
directly proportional
Light ________ need a medium to travel because it is not a _____________ wave.
doesn't, mechanical
four interactions between light and matter
emission absorption transmission reflection/scattering
electron light
emitted
ionizing radiation
enough energy to dislodge electrons from atoms, forming ions; capable of causing cancer
examples of ionizing radiation
gamma rays, x-rays, higher UV
What light waves will not make it to earth's surface?
gamma rays, x-rays, most uv, some infrared
Which color of light, emitted by the Sun, is the brightest?
green More green light is emitted than any other color of light by the Sun.
The direction of propagation of an electromagnetic wave is
in a direction perpendicular to both the electric field and the magnetic field. Transverse waves travel in a direction perpendicular to the direction of the oscillations associated with the wave.
What determines the apparent light speed?
index of refraction
energy of light and wavelength relationship
inversely proportional
What kinds of molecules will scatter the low frequencies of light?
large molecules
electromagnetic radiation
light a kind of radiation including visible light, radio waves, gamma rays, and X-rays, in which electric and magnetic fields vary simultaneously.
duality of light
light is both a particle and a wave
source and receiver mover farther apart
longer wavelengths, lower frequencies
examples of non-ionizing radiation
lower uv, visible light, infrared, radio
radio sources
manmade, cosmic
Transparency is dependent on
material, clarity, frequency
Do neutrons give off light?
no, light waves are caused by accelerating charged particles (electrons and protons)
Is the upper atmosphere of the earth opaque or transparent?
opaque
Rank electromagnetic spectrum from lowest to highest energy
radio, microwave, infrared, visible light, ultraviolet, x-rays, gamma rays
proton light
radioactive
What color light is transmitted through a piece of red glass?
red
What part of the visible electromagnetic spectrum is most absorbed by water? Violet Green Red Blue
red
Sunlight is made up of roughly equal amounts of blue, green, yellow, and red light. As the sunlight goes through our atmosphere, which type of light gets to an observer during sunset.
red Red light scatters the least, so more red light reaches the observer than other colors.
source and receiver move closer together
shorter wavelengths, higher frequencies
light with _____ wavelengths is scattered more than light with _________ wavelengths
shorter; longer
What kinds of molecules scatter high frequencies of light?
small molecules
light moves in a __________ line unless materials causes it to refract.
straight
Ultraviolet sources
supernova remnants; hot young stars
How does frequency change when wavelength is increased?
the frequency decreases
For an electromagnetic wave passing a particular point in space, if at some moment in time the electric field of the wave is zero, then
the magnetic field at that same location and time is also zero. The electric and magnetic fields oscillate in phase, so when one field is zero, so is the other.
Is the atmosphere near the surface of the earth transparent or opaque?
transparent
What level of the earth's atmosphere absorbs gamma rays, x-rays, and most uv rays?
upper atmosphere
Rank light speed mediums from fastest to slowest
vacuum, air, water, diamond
What is the fundamental source of electromagnetic radiation?
vibrating electric charges, which emit vibrating electric and magnetic fields
What is the color of visible light with the highest frequency?
violet
What are the principal differences between an x-ray and visible light?
visible light waves have a lower frequency and longer wavelength
What light waves will make it to the earth's surface?
visible light, radio, some uv, some infrared
If the amplitude of green light increases, the frequency of the light wave
wouldn't change The frequency of light simply depends on the wavelength. It does not depend on the amplitude.