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Midterm 3 Flashcards

1
Q

Whichofthefollowingstatementsbestdescribesthequantumpropertyspin?
A)Spinisameasureoftherotationrateofasubatomicparticle
B)Spinisnotmeanttobetakenliterallybutmeasurestheinherentangularmomentumofasubatomicparticle.
C)Spinisapropertythatappliesonlytolargeobjects,likebaseballs.
D)Spinisameasureoftherateatwhichaparticlespinsaround(orbits)anotherparticle.
E)Spinisnotafundamentalpropertybutrathersomethingthatcanchangerandomlyatanytime.

A

Spinisnotmeanttobetakenliterallybutmeasurestheinherentangularmomentumofasubatomicparticle.

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2
Q

Anupquark(u)hasacharge+2/3,andadownquark(d)hasachargeof—1/3.Whichofthefollowingdescribesaproton?

A

uud

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3
Q

Thetwofamiliesof
fundamentalparticlesoutof
whichallordinarymattersmadeare

A

leptonsandquarks.

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4
Q

Thefourfundamentalforcesare

A

strongforce,weakforce,electromagneticforce,gravity

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5
Q 
Supposethat,throughthemalicious
actofaneight-dimensionalalienbeing,
thestrongforcewassuddenlyturned
offthroughouttheuniverse.Whatwould
happenalmostimmediatelytoatoms?
A

Thenucleiofatomswouldfallapart.

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6
Q

Accordingtotheuncertaintyprinciple,

whichofthefollowingstatementsistrue?

A

Itisimpossibletomeasureboththeposition
andthevelocity ofaparticleatthe
sametime.

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7
Q 
Whichofthefollowingstatementsbest
describestheexclusionprinciple?
A)Ifaparticlehasapreciselydefinedposition,
itisexcludedfromhavingapreciselydefined
momentum.
B)Twophotonscannotbeinthesameplace
atthesametime.
C)Thelawsofquantummechanicsare
excludedfromapplyingtolargeobjects
madeofmanyatoms.
D)Thelawsofquantummechanicsare
excludedfromourcommonsense.
E)Twofermionscannotoccupythesame
quantumstateatthesametime.
A

Twofermionscannotoccupythesame

quantumstateatthesametime.

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8
Q 
Whichofthefollowingwillcause
thedegeneracypressurewithinanobject
toincrease?
A)compressingittohigherdensity
B)loweringitstemperature
C)lettingitexpandtolowerdensity
D)raisingitstemperature
E)shiningalightonit,whichaddsradiative
energy
A

compressingittohigherdensity

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9
Q

Whichofthefollowingstatementsabout
quantumtunnelingistrue?
A)Itisusedinmodernelectronics,and,
infact,ourmodern daycomputers
wouldnotworkwithoutit.
B)Itplaysacrucialroleinnuclearfusion
intheSun.
C)Itallowselectronsandothersubatomic
particlestopassthroughwall-likeenergy
barriersevenwhenitseemstheydo
nothaveenoughenergytogetthroughthebarriers.
D)Althoughithasbeenobservedtooccur,
itviolatesallotherknownlawsofnature,
andexplainingittherefore
representsamajorchallengetophysicists.
E)A,B,andCaretrue,butDisnot

A

E)A,B,andCaretrue,butDisnot

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10
Q

Whichofthefollowingbestexplains
thephenomenonofblackholeevaporation?
A)Blackholeevaporationisavirtualprocess,
meaningthatithasbeentheorizedbyastrophysicistsbutdoesn’treally
occur.
B)Particles(orantiparticles)arecreatedby
aquantummechanicaleffectnear,butoutside,
theeventhorizonoftheblack
hole.Thelawofconservationofenergymaintains
thattheblackholemustloseenergyto”pay”forthecreationofthis
mass.
C)Virtualparticlescreatedneartheblack
holeareconstantlyannihilatingeachother,causinga
veryhightemperature
eveniftheblackholehasnoaccretiondisk.
Thishightemperatureprovidesescapevelocityforthe
virtualparticles,causingtheentire”cloud”ofvirtualparticles
toexpandawayintospace.
D)Duetohightemperaturesintheaccretiondiskarounda
blackhole,materialevaporatesfromtheblackholelikewater
evaporatingfromtheocean.
E)Particles(orantiparticles)areoccasionallyejectedfrom
withintheeventhorizon,causingtheblackholetolosemass.

A

Particles(orantiparticles)arecreatedbya
quantummechanicaleffectnear,
butoutside,theeventhorizonofthe
blackhole.Thelawofconservationofenergy
maintainsthattheblackholemustloseenergyto
“pay”forthecreationofthis
mass.

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11
Q

Whichofthefollowingstatementsabout
degeneracypressureisnottrue?
A)Degeneracypressurestopsthegravitational
collapseofordinary(main­sequence)starsliketheSun.
B)Degeneracypressurearisesonlywith
fermions(suchaselectrons,protons,andneutrons)
andnotwithbosons(suchasphotonsorheliumnuclei).
C)Degeneracypressurestopsthegravitational
collapseofwhitedwarfs.
D)Explainingtheoriginofdegeneracy
pressurerequiresboththequantummechanicalexclusionprincipleandthe
uncertaintyprinciple.
E)Degeneracypressurehaltsthecollapse
ofneutronstars.

A

Degeneracypressurestopsthe

gravitationalcollapseofordinary(main­sequence)starsliketheSun.

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12
Q

Inthelate1800s,KelvinandHelmholtz
suggestedthattheSunstayedhot
thankstogravitationalcontraction.
Whatwasthemajordrawbackofthisidea?

A

ItpredictedthattheSuncouldlast
onlyabout25millionyears,whichis
farlessthantheageofEarth.

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13
Q

Whatdowemeanwhenwesaythat

theSunisingravitationalequilibrium?

A

ThereisabalancewithintheSun
between theoutwardpushofpressure
andtheinwardpullofgravity.

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14
Q

WhatistheSunmadeof?

A

70percenthydrogen,28percenthelium,

2percentotherelements

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15
Q

ThephaseofmatterintheSunis

A

plasma.

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16
Q

Fromthecenteroutward,whichofthe
followingliststhe”layers”oftheSun
inthecorrectorder?

A

core,radiationzone,convectionzone,

photosphere,chromosphere,corona

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17
Q

Sunspotsarecoolerthanthe

surroundingsolarsurfacebecause

A

strongmagneticfieldsslow
convectionandpreventhotplasma
fromenteringtheregion.

18
Q

Thefirststepintheproton­protonchainproducesananti­electron,orpositron.
Whathappenstothepositron?

A

Itisrapidlyconvertedtoenergywhen
itmeetsanordinaryelectron,resulting
inmatter­antimatterannihilation.

19
Q

Theoverallfusionreactionbywhich

theSuncurrentlyproducesenergyis

A

4H 1He+energy.

20
Q

Supposethat,forsomeunknownreason,
thecoreoftheSunsuddenlybecamehotter.
Whichofthefollowingbest
describeswhatwouldhappen?
A)Thehighertemperaturewouldnotaffect
thefusionratebutwouldcausethecoretoexpand
andcooluntilthetemperaturereturnedtonormal,
withthecoreatanew,slightlylargersize.
B)Highertemperaturewouldcausetherateof
nuclearfusiontorise,whichwouldincreasethe
internalpressure,causingthecoretoexpandand
turntheSunintoagiantstar.
C)Highertemperaturewouldcausetherateof
fusiontofall,decreasingtheinternalpressure
andcausingthecoreto
collapseuntiltherateoffusionreturnedtonormal.
D)Highertemperaturewouldcausetherateof
nuclearfusiontorise,whichwouldincreasethe
internalpressure,causing thecoretoexpandandcooluntilthe
fusionratereturnedtonormal.

A

Highertemperaturewouldcausetherateof
nuclearfusiontorise,whichwouldincrease
theinternalpressure,causing thecoretoexpandandcooluntilthe fusionratereturnedtonormal.

21
Q

Whathappenstoenergyintheconvectionzoneof

theSun?

A

Energyistransportedoutwardbytherising

ofhotplasmaandthesinkingofcoolerplasma.

22
Q

Whatprocessesareinvolvedinthesunspot

cycle?

A

thewindingofmagneticfieldlinesdueto

differentialrotation

23
Q

Sinceallstarsbegintheirliveswiththesame
basiccomposition,whatcharacteristicmost
determineshowtheywilldiffer?

A

masstheyareformedwith

24
Q

Astar’sluminosityisthe

A

totalamountoflightthatthestarwill

radiateoveritsentirelifetime.

25
If the distance between us and a star is  doubled, with everything else remaining the  same, the luminosity 
remains the same, but the apparent  | brightness is decreased by a factor of four. 
26
Suppose that you measure the parallax  angle for a particular star to be 0.5 arcsecod.  The distance to this star is 
 2 parsecs. 
27
Which of the following statements about spectral  types of stars is true? A) A star with spectral type A is cooler than a  star with spectral type B.  B) The spectral type of a star can be used to  determine its surface temperature.  C) The spectral type of a star can be used to  determine its color.  D) A star with spectral type F2 is hotter than a star with spectral type F3.  E) All of the above are true. 
All of the above are true. 
28
Suppose you see two main-sequence stars  of the same spectral type. Star 1 is dimmer in  apparent brightness than Star 2 by a factor of 100.  What can you conclude? (Neglect any effects that might  be caused by interstellar dust and gas.) 
Star 1 is 10 times more distant than Star 2. 
29
Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by  measuring their periodic Doppler shifts?  A) double star  B) spectroscopic binary  C) visual binary  D) eclipsing binary  E) none of the above 
spectroscopic binary 
30
On a Hertzsprung-Russell diagram, where would we find  | stars that have the largest radii?
 upper right 
31
 You observe a star in the disk of the  Milky Way, and you want to plot the star on  an H-R diagram. You will need to determine all of the following, except the 
 rotation rate of the star
32
``` Which of the following is true about low­mass stars compared to high­mass stars? A) Low mass stars are hotter and more  luminous than high­mass stars.  B) Low ­mass stars are cooler and less  luminous than high­mass stars.  C) Low ­mass stars are cooler but more  luminous than high­mass stars.  D) Low mass stars have the same temperature  and luminosity as high­mass stars.  E) Low mass stars are hotter but less  luminous than high­mass stars.  ```
Low­mass stars are cooler and  | less luminous than high­mass stars. 
33
Why are Cepheid variables so important  | for measuring distances in astronomy? 
Their luminosity can be  | inferred from their period.
34
 Cluster ages can be determined from 
main sequence turnoff. 
35
The typical density and temperature of  | molecular clouds are
300 molecules per cubic  | centimeter, 10­30 Kelvin. 
36
 If you wanted to observe stars behind  a molecular cloud, in what wavelength  of light would you most likely  observe?
infrared 
37
The thermal pressure of a gas depends  | on
density and temperature. 
38
What prevents the pressure from  increasing as a cloud contracts  due to its gravity?
 Excess pressure is released in  | jets of material from the young stars.
39
What is the likely reason that  we cannot find any examples  of the first generation stars?
The first generation stars were  | all very massive and exploded as supernova.
40
 When does a star  | become a main­sequence star?
when the rate of hydrogen fusion within the star's core is  | high enough to maintain gravitational equilibrium 
41
Which of the following discoveries,  if they existed, would necessitate  a reevaluation of our ideas of stellar  formation?
a 0.01­ | solar­mass star
42
 What prevents a brown dwarf  | from undergoing nuclear fusion?
Degeneracy pressure halts the contraction  of a protostar so the core never becomes  hot or dense enough for nuclear fusion. 

Astronomy (3 decks)

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