Exam 3
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.
Distinguish between fluorescence and phosphorescence.
Phosphorescence has a longer time delay between excitation and emission. Fluorescence, UV light excites atoms, which emit visible light when de-excited. (detergents, paints, crayons.) Phosphorescence, electrons are boosted then become "stuck", delay before de-excitation.
Distinguish between the primary and secondary excitation processes that occur in a fluorescent lamp.
Primary excitation is when electrons collide with and excite mercury gas. Secondary excitation is when ultraviolet light from the mercury excites a phosphor to emit visible light.
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
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 speed of light in a vacuum (in m/s)?
300 million m/s
speed of sound
340 m/s
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."
absorption line spectrum
A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.
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
How does the avalanche of photons in a laser beam differ from the hordes of photons emitted by an incandescent lamp?
A laser beam propagates in one direction, with one wavelength that is all in phase (coherent, retains intensity). Light from an incandescent lamp does none of these (incoherent, spreads, loses intensity with distance).
What is a metastable state?
A metastable state is a long-lived excited state. "A prolonged state of excitation. Can be several hours. If the source of excitation is removed, an afterglow remains while millions of atoms spontaneously undergo gradual de-excitation. Older clock dials containing radium or other radioactive material continuously supplying energy glow indefinitely in the dark." Bioluminescence of creatures!
incandescence
A process that makes light with heat (thermal radiation)
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 do the various colors displayed in the flame of a burning log indicate?
The colors of the flames indicate the types of atoms that are emitting light in the flame. Ex. salt in a flame produces characteristic yellow of sodium.
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 is the peak frequency of emitted light related to the absolute temperature of its incandescent source?
The peak frequency is proportional to the absolute temperature. f=T
Why are fabrics that fluoresce when exposed to ultraviolet light so bright in sunlight?
These clothes (or the detergent used) contain fluorescent dyes that convert the UV light in sunlight into blue visible light, so they reflect more blue light than they otherwise would. The clothes appear whiter and brighter.
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.
Fluorescence is activated by _________ light.
UV
Phosphorescence is activated by _________ light.
UV
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.
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
de-excitation creates
a photon of light
light
a propagating, oscillating electric field & magnetic field
according to the laws of thermal radiation, hotter objects emit photons with
a shorter average wavelength
continuous spectrum graph
a solid sweeping line with no spikes
opaque materials
absorb light without re-emitting it
if we say that a material is opaque to ultraviolet light, we mean that it....
absorbs ultraviolet light
Name the four basic interactions between light and matter:
absorption emission reflection/scattering transmission
hot light source and cooler gas produces
absorption line spectrum
What are Fraunhofer lines?
absorption lines
What type of spectrum does light reflected from a planetary atmosphere produce?
absorption spectrum
What type of spectrum does the Sun produce?
absorption spectrum
a hot, high density source passing through a cool, low-density medium produces
absorption spectrum
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
If you know the wavelength of any form of electromagnetic radiation, you can determine its frequency because a) all wavelengths travel at the same speed b) the speed of light varies for each form c) wavelength and frequency are equal d) the speed of light increases as wavelength increase
all wavelengths travel at the same speed
purposes of the eye
allow light to enter: pupil control how much light enters: iris refracts light: lens interpretation of light: retina
transparent materials
allow light to pass through can see through them
intensity/brightness of light
amplitude of light waves
emission occurs when
an electron is de-excited
continuous spectrum
an even distribution of radiation over all wavelengths thus, all colors are present
What gives off infrared light?
any object in the universe that has density (mass & volume)
lens (eye)
bends entering light rays and focuses them onto the retina
The shortest wavelength visible light of those listed below is yellow red green blue
blue
what light is hotter? red, white, or blue
blue
Which has the higher frequency, red light or blue light?
blue light
Which is hotter? red star blue star planet that emits infrared light
blue star
What color light does mercury emit?
blues and violets
relative shortening between wave crests, yielding shorter wavelength and higher frequency
blueshift, approaching
When red light is compared with violet light: a) both have the same frequency b) both have the same wavelength c) both travel at the same speed d) red light travels faster than violet light
both travel at the same speed
telescope CCD camera
catches multiple photons over time, can see faint images
set of spectral lines that we see in a star's spectrum depend on the star's
chemical composition
The ____________ an electron is to its nucleus (protons), the more ionizing energy it requires.
closer
Is the atmosphere near the earth hotter or colder than the upper atmosphere?
colder due to upper atmosphere absorbing majority of light waves
frequency of light
color
The peak of the continuous part of the spectrum represents the highest quantity of:
color frequency
iris (eye)
colored portion of the eye that allows light to enter the eye
emission line spectrum is dependent on
composition and temperature higher temp; brighter color lines
What spectrum does incandescence produce?
continuous
a hot, high density light produces
continuous spectrum
hot light source produces
continuous spectrum
a star whose spectrum peaks in the infrared is
cooler than our Sun.
absorption line graph
has clusters of downward spikes
emission line spectrum graph
has clusters of upward spikes
An electron can be ejected from an atom if it absorbs a photon that
has more energy than is needed to raise the electron to the highest energy level
the spectra of most galaxies show redshifts. this means that their spectral lines
have wavelengths that are longer than normal
LED's do not lose energy to
heat
thermal radiation
heat transfer in the form of electromagnetic waves, including light
an absorption spectrum is produced by
hot, high-density light source shining through a cool, thin gas
What is a spectroscope, and what does it accomplish?
A spectroscope displays the spectrum of light as brightness versus wavelength.
emission line spectrum
A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines.
A lamp filament is made of tungsten. Why do we get a continuous spectrum rather than a tungsten line spectrum when light from an incandescent lamp is viewed with a spectroscope?
Because when tungsten atoms are close-packed in a solid, the otherwise will-defined energy levels of outer electron shells are smeared by mutual interactions among neighboring atoms.The hot filament emits a continuous spectrum, mostly in the infrared, with visible light as the smaller, useful part. (black-body radiation factor?)
Hydrogen Absorption Spectrum
Black lines indicate the wavelengths of light that are absorbed
Why is the sky blue?
Blue light is scattered by the atmosphere more than other colors.
Which has the higher frequency: red or blue light? Which has the greater energy per photon: red or blue light?
Blue light, blue light. "A photon in a beam of red light carries an amount of energy corresponding to its frequency." Low frequency = low energy. "A photon of twice the frequency has twice the energy; found in UV part of spectrum, blue." Higher frequency = hi energy.
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
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 is the state of glowing visibly while at high temperature?
incandescence
what type of light is thermal radiation?
incandescence
Examples of manmade sources of light
incandescence: light bulb (1000 hrs of light) fluorescent: light bulb (10,000 hrs of light) CFL: infrared LED: light bulbs (100,000 hrs of light) LASER: monochromatic
common light
incandescent light
What determines the apparent light speed?
index of refraction
What light do people emit?
infrared
energy of light and wavelength relationship
inversely proportional
Human eye parts
iris, pupil, retina (cones & rods), optical nerve
An object's thermal radiation spectrum depends on only one property:
its temperature
photons have a ________ amount of energy together.
large
What kinds of molecules will scatter the low frequencies of light?
large molecules
The human eye is a device that collects___________, it is a natural imaging system.
light
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.
phosphorescence
light emitted by a substance without combustion or perceptible heat
luminescence
light from non-thermal sources
duality of light
light is both a particle and a wave
transmission
light passing through matter whatever is not transmitted is absorbed
photons have a __________ amount of energy individually.
little
source and receiver mover farther apart
longer wavelengths, lower frequencies
an emission spectrum is produced by
low-density, hot gas
examples of non-ionizing radiation
lower uv, visible light, infrared, radio
a continuous spectrum is produced by
luminous solid or liquid, or a sufficiently dense gas
radio sources
manmade, cosmic
Transparency is dependent on
material, clarity, frequency
Fluorescence
materials that are excited by higher energy light than re-emit lower energy light.
absorption
matter absorbs energy of light; whatever is not absorbed is transmitted
reflection/scattering
matter causes light to change direction
emission
matter emits light via electrons of the atoms
the electron that loses the most energy is one that
moves the greatest distance between the energy levels in its downward transition
De-excitation
moving an electron from higher energy to lower level.
excitation
moving an electron from lower to higher energy state
Do neutrons give off light?
no, light waves are caused by accelerating charged particles (electrons and protons)
ionization energy is dependent on the
number of protons the orbital the electron resides
A radiating source is moving away from observer A and toward observer B. How does the distance between the waves compare for observer A and observer B?
observer A detects a greater distance between wave crests than observer B
A radiating source at rest with respect to two observers equally apart on either side of the source. How do the waves detected by observer A compare to those detected by observer B?
observer A detects the same wavelength and the same frequency as observer B
If you are reading a book and you move twice as far away from the light source, how does the brightness at the new distance compare with that at the old distance? It is: a) one-eighth as bright b) one-fourth as bright c) one-half as bright d) twice as bright
one-fourth as bright
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.
x-ray sources
High voltage x-Ray tubes, stars and galaxies
Wein's Law
Hotter objects emit photons with a higher average energy
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."
selective transmission
only some wavelengths pass through the object or substance
Is the upper atmosphere of the earth opaque or transparent?
opaque
What color light does sodium emit?
orange-yellow
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
telescopes
Instruments that collect and focus light and other forms of electromagnetic radiation
the color of a transparent object depends on the color of the light it transmits
selective transmission
source and receiver move closer together
shorter wavelengths, higher frequencies
light with _____ wavelengths is scattered more than light with _________ wavelengths
shorter; longer
emission spectrum
shows only the specific colors being emitted. Black regions represent the absence of light.
What kinds of molecules scatter high frequencies of light?
small molecules
What is the optical instrument that separates light into its constituent wavelengths?
spectrometer
astronomers use _____________ to determine the composition, density, and temperature of celestial objects.
spectroscopy
examples of selective transmission
stained glass, colored jewels
light moves in a __________ line unless materials causes it to refract.
straight
Examples of incandescent light
sun, people, light bulbs, block of ice
Ultraviolet sources
supernova remnants; hot young stars
telescope eyepiece
takes light and refocuses it at the retina, real time only
Examples of fluorescence
teeth enamel scorpions minerals
continuous spectrums are dependent on
temperature of object more heat, bright spectrum
scattering depends on
the atoms/molecules of the matter size of object and its particles wavelengths of light ROYGBIV
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 does frequency change when wavelength is increased?
the frequency decreases
pupil (eye)
the light collection site
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.
The farther light is from a source: a) the more spread out light becomes b) the more condensed light becomes c) the more bright light becomes d) the more light is available per unit area
the more spread out light becomes
Electroluminescence
the process of transforming electrical energy directly into light energy
absorption line spectrum depends on
the properties of the cloud of gas itself
electromagnetic spectrum
the range of wavelengths or frequencies over which electromagnetic radiation extends.
spectral fingerprint
the spectrum mapping of each atom
continuous line spectrum
the spectrum of common (incandescent) light bulb spans all visible wavelengths without interuption
spectroscopy
the study of the interaction of electromagnetic radiation with matter
Why are clouds white?
their water droplets or ice crystals are large enough to scatter the light of the seven wavelengths (red, orange, yellow, green, blue, indigo, and violet), which combine to produce white light.
Nearly all large or dense objects emit ________________________, including stars, planets, and you.
thermal radiation
Is the atmosphere near the surface of the earth transparent or opaque?
transparent
air is _____________ to visible light.
transparent
Cornea (eye)
transparent tissue where light enters the eye
Which portion of the electromagnetic spectrum is used to identify fluorescent minerals? a) ultraviolet light b) X rays c) infrared waves d) gamma rays
ultraviolet light
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
The source of all electromagnetic waves is
vibrating charged particles
What is the fundamental source of electromagnetic radiation?
vibrating electric charges, which emit vibrating electric and magnetic fields
Which portion of the electromagnetic spectrum is used in a microscope? a) infrared waves b) X rays c) visible light d) ultraviolet light
visible light
What are the principal differences between an x-ray and visible light?
visible light waves have a lower frequency and longer wavelength
Electrons made to vibrate to and fro at a few hundred thousand hertz emit radio waves. What class of waves is emitted from electron vibrations of a few million billion hertz?
visible light waves would be emitted. Light emission from atoms involve transitions of electrons from higher to lower energy states within atom.
What light waves will make it to the earth's surface?
visible light, radio, some uv, some infrared
Examples of transparent light waves
visible, radio, some UV, some infrared
If you know the frequency of any form of electromagnetic radiation, you can determine its
wavelength E/f=h
selective reflection
when an object reflects some wavelengths of the spectrum more than others
retina (eye)
where light begins to get transformed into neural impulses to be sent out of the optic nerve contains rods and cones
Conditions to see a rainbow
white light (usually from sun) rain observer standing between the sun and rain
electrons only exist on __________ energy levels, not ________ energy levels.
whole; partial
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.
Which of the following types of light has the highest frequency? visible infrared radio waves x-rays
x-rays
The human eye is most sensitive to which portion of the EM spectrum?
yellow/orange 535 nm
Do xrays have an incandescence component?
yes
In a neon tube, what occurs immediately after an atom is excited?
It de-excites and emits light. Electrons are boiled off electrodes at tube ends, jostling at high speeds by AC voltage; smashing boosts orbital e- into higher energy levels. The energy is radiated as red light (neon) and e- fall back to stable orbits (ground state).
How does the total energy per unit area emitted by the object change when you increase the temperature, and how do we know this from the graph provided?
It increases, the area under the graph increases when the temperature increases
Why is a rose red?
It scatters red light
Developed in the 1960s, ___________ emit light electrically by use of semiconducting materials.
LED
example of electroluminscence
LED (light emitting diodes)
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
Opaque objects reflect the color seen and absorb all other colors
selective reflection
Properties of Thermal Radiation
1. Hotter objects emit more light at all frequencies per unit area (stefan-boltzman law) 2. Hotter objects emit photons with a higher average energy. (wein's law
What is the frequency of infrared light of 1.0x10-⁴ Hz frequency? a) 0.050 m b) 0.060 m c) 0.10 m d) 0.20 m
.10 m
light speed through diamond
.41C
light speed through glass
.67C
light speed through water
.75C
Name three types of spectra:
1. Continuous 2. Emission 3. Absorption
Why is argon, instead of air, used inside an incandescent bulb?
Air contains oxygen that would react with and destroy the tungsten filament. Argon is an inert noble gas.
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).
How does an absorption spectrum differ in appearance from an emission spectrum?
An emission spectrum consists of bright lines against a dark background, whereas an absorption spectrum consists of dark lines against a bright rainbow background.
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."
What is the evidence for the claim that iron exists in the relatively cool outer layer of the Sun?
Analysis of the Fraunhofer lines of the Sun's spectrum reveal the chemical composition of the atmosphere. The stellar elements are the same elements existing on Earth. The many absorption lines must have also proved iron exists in this cooler gas outer layer.
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.
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
How does the potential energy relative to the nucleus of an electron depend on whether it is in an inner electron shell or an outer electron shell?
Electrons in outer shells have higher potential energy. Similar to energy of a spring door or pile driver. The wider the door is open, higher spring potential energy; higher pile driver lifted, greater gravitational potential energy.
When a gas glows, discrete colors are emitted. When a solid glows, the colors are smudged. Why?
Emitting electrons interact with nearby neighboring atoms in a solid. In a gas, there are few nearby atoms. Think of the clear frequency of a single ringing bell, vs the smudged sound of a crowded box of bells.
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
How can a hydrogen atom, which has only one electron, have so many spectral lines?
Every transition from one of those levels to another is a spectral line. The spectral lines correspond to the electron transitions between atomic levels, characteristic of each element. The spectral lines represent the wavelengths of light given off when an electron changes energy levels. Even a simple system with two particles (electron and nucleus) has an infinite number of energy levels available to it.
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.
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
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
Which puts out the greater percentage of its energy as visible light: an incandescent lamp or a mercury-vapor lamp? How is the remaining non-visible light energy emitted?
Mercury-vapor lamp; incandescent lights emit more in the infrared. Mercury emits blues and violets; Sodium emits orange-yellow.
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.
Stefan-Boltzmann Law
P ∝ T⁴ Each square meter of a hotter object's surface emits more light at all wavelengths
Why don't we glow in the dark?
People only emit light that is invisible to our eyes.
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
Hotter objects emit more light at all frequencies per unit area.
Stefan-Boltzmann Law
Distinguish between monochromatic light and sunlight.
Sunlight has a wide range of frequencies and wavelengths, whereas monochromatic light has one wavelength and one frequency (filtered, though still incoherent, out of phase waves).
Distinguish between coherent light and sunlight.
Sunlight has a wide range of frequencies, wavelengths, and phases, whereas coherent light has one wavelength, one frequency, and one phase. A beam of photons (laser) have same frequency, phase and direction, identical copies of each other. Spreads and weakens very little.
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*
How does the lifetime of a typical CFL compare with the lifetime of an incandescent bulb?
The CFL lasts more than 10 times longer. Similar to a mini incandescent, coiled, with a gas filled tube, and magnetic or electronic ballast. Still contains mercury. Offers 4X the light.
How can astrophysicists tell whether a star is receding from or approaching Earth?
The Doppler shift of spectral lines is red for receding and blue for approaching. Measure the frequency emitted by the source, not the speed.
How does the lifetime of a typical LED compare with the lifetime of an incandescent bulb?
The LED lasts 100 times longer. Compact, efficient, require no filament, and have no mercury. Diodes convert ac to dc in electric circuits. LED is a reverse photocell; an impressed voltage stimulates light emission.
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.
What creates the photon of electron light emission?
The difference of energy levels when an electron moves down from a higher level to a lower level.
What is it exactly that waves in a light-wave?
The electric and Magnetic fields
How is the energy of a photon related to its vibrational frequency?
The energy is proportional to the frequency. E~f "The frequency of the photon is directly proportional to its energy. E=hf (Planck's)
How does the difference in energy between energy levels relate to the energy of the photon that is emitted by a transition between those levels?
The energy of the photon is equal to the difference in energy between the energy levels. E~f Electrons dropping from hi to low energy levels in an excited atom emit with each jump a throbbing pulse of electromagnetic radiation (photon) with frequency related to the energy transition of the jump. E=hf
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.
How does the intensity at a given wavelength change if you increase the temperature?
The intensity increases
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.
ground state
The lowest energy state of an atom
optically dense
The measure of transmittance of an optical medium for a given wavelength
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
dispersion of light
The separating of light into its different colours
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 does it mean to say an energy state is discrete?
The state has a precise energy. These states are found only at certain energies.
Why is ultraviolet light, but not infrared light, effective in making certain materials fluoresce?
The ultraviolet light photons have higher energy than visible light photons, whereas the infrared have lower energy. Thus, some of the ultraviolet energy can be reemitted as visible color.
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 does the wavelength at which the maximum intensity occurs change when you increase the temperature?
The wavelength decreases
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.
Why is the ocean blue?
The wavelengths of blue light can penetrate much deeper than those of other colors.
Ultraviolet light causes sunburns, whereas visible light, even of greater intensity, does not. Why is this so?
There is more energy associated with each photon of ultraviolet light than with visible light. Visible light mostly just heats the skin, but not enough to cause thermal burns.
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
Can a neon atom in a glass tube be excited more than once? Explain.
Yes. The electrons in the atom stay with the same atom as it is excited and de-excited by one collision after another. "Millions of e- vibrate back and forth, smashing...the process occurs and recurs many times, as neon atoms continuously undergo a cycle of excitation and de-excitation. The overall result is transformation of electric energy into radiant energy."
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.
emission spectra
a characteristic pattern of frequencies emitted by every element. Each element has different number of protons and electrons.
diffraction grating
a device made of thousands of closely spaced slits through which light is passed in order to produce a spectrum
spectrometer
a device that spreads light into its different colors
Light can appear to slowdown depending on the ___________ of the matter it is traveling through.
density
rods
detect black, white, and gray (peripheral and night vision) intensity/brightness of light (amplitude)
cones
detect fine detail and color in bright light absorbs frequency to detect the color
energy of light and frequency relationship
directly proportional
telescope spectrometer
disperses light to see its colors using lenses, prisms, slits, or diffraction grating
Light ________ need a medium to travel because it is not a _____________ wave.
doesn't, mechanical
In excitation, ____________ are boosted from lower to higher energy levels in an atom.
electrons
four interactions between light and matter
emission absorption transmission reflection/scattering
thin or low density cloud of gas produces
emission line spectrum
What kind of spectrum does a hot nebula produce?
emission spectrum
a hot, low-density source produces
emission spectrum
electron light
emitted
Adding ________ to electrons will only move it to the next energy level after the threshold has been met.
energy
Each type of atom has an unique set of ________ levels.
energy
E=hc/λ
energy and wavelength equation
E=hf
energy of a photon
ionizing radiation
enough energy to dislodge electrons from atoms, forming ions; capable of causing cancer
additions to a telescope
eyepiece CCD camera spectrometer
The ________ an electron is to its nucleus, the less ionizing energy it requires
farther
Examples of bioluminescence
fireflies, bacteria, algae, squid, octopus, jellyfish
What type of light has no delay between excitation and de-excitation?
fluorescence
Types of Luminescent Light
fluorescence, phosphorous, bioluminescence
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
examples of opaque light waves
gamma, xrays, most UV, some infrared
examples of phosphorescence
glow in the dark
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.
electrons are always seeking its
ground state
Bioluminescence
organisms using chemical in their bodies to emit light
What is a type of light emission where there is a delay between excitation or de-excitation, providing an afterglow?
phosphorescence
What type of light has a time-delay between excitation and de-excitation?
phosphorescence
if photon A has a higher energy than photon B, then it also true that
photon A has a higher frequency and shorter wavelength than photon b
Which of the following types of light has the lowest energy per photon? visible infrared radio waves x-rays
radio waves
Which portion of the electromagnetic spectrum is used in a television? a) infrared waves b) X rays c) radio waves d) gamma waves
radio waves
Rank electromagnetic spectrum from lowest to highest energy
radio, microwave, infrared, visible light, ultraviolet, x-rays, gamma rays
proton light
radioactive
Why do rainbows occur?
raindrops act like tiny prisms. They bend the different colors in white light, so the light spreads out into a band of colors that can be reflected back refract on entering front of the raindrop, reflect on the back of raindrop, refract again exiting the front of the raindrop
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.
relative stretching between wave crests, yielding longer wavelength and lower frequency
redshift, receding
light emission
released by electrons as they return to the ground state (lower energy level) from their excited state (higher energy level)
absorption spectrum
resembles a continuous spectrum but has narrow black lines where light is absorbed. (black=absence of color, wavelengths absorbed)
