Exam 3

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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)


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