Midterm 3

Question 1

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

Answer 1

Spinisnotmeanttobetakenliterallybutmeasurestheinherentangularmomentumofasubatomicparticle.

Question 2

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

Answer 2

uud

Question 3

Thetwofamiliesof
fundamentalparticlesoutof
whichallordinarymattersmadeare

Answer 3

leptonsandquarks.

Question 4

Thefourfundamentalforcesare

Answer 4

strongforce,weakforce,electromagneticforce,gravity

Question 5

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

Answer 5

Thenucleiofatomswouldfallapart.

Question 6

Accordingtotheuncertaintyprinciple,

whichofthefollowingstatementsistrue?

Answer 6

Itisimpossibletomeasureboththeposition
andthevelocity ofaparticleatthe
sametime.

Question 7

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

Answer 7

Twofermionscannotoccupythesame

quantumstateatthesametime.

Question 8

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

Answer 8

compressingittohigherdensity

Question 9

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

Answer 9

E)A,B,andCaretrue,butDisnot

Question 10

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.

Answer 10

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

Question 11

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.

Answer 11

Degeneracypressurestopsthe

gravitationalcollapseofordinary(main­sequence)starsliketheSun.

Question 12

Inthelate1800s,KelvinandHelmholtz
suggestedthattheSunstayedhot
thankstogravitationalcontraction.
Whatwasthemajordrawbackofthisidea?

Answer 12

ItpredictedthattheSuncouldlast
onlyabout25millionyears,whichis
farlessthantheageofEarth.

Question 13

Whatdowemeanwhenwesaythat

theSunisingravitationalequilibrium?

Answer 13

ThereisabalancewithintheSun
between theoutwardpushofpressure
andtheinwardpullofgravity.

Question 14

WhatistheSunmadeof?

Answer 14

70percenthydrogen,28percenthelium,

2percentotherelements

Question 15

ThephaseofmatterintheSunis

Answer 15

plasma.

Question 16

Fromthecenteroutward,whichofthe
followingliststhe”layers”oftheSun
inthecorrectorder?

Answer 16

core,radiationzone,convectionzone,

photosphere,chromosphere,corona

Question 17

Sunspotsarecoolerthanthe

surroundingsolarsurfacebecause

Answer 17

strongmagneticfieldsslow
convectionandpreventhotplasma
fromenteringtheregion.

Question 18

Thefirststepintheproton­protonchainproducesananti­electron,orpositron.
Whathappenstothepositron?

Answer 18

Itisrapidlyconvertedtoenergywhen
itmeetsanordinaryelectron,resulting
inmatter­antimatterannihilation.

Question 19

Theoverallfusionreactionbywhich

theSuncurrentlyproducesenergyis

Answer 19

4H 1He+energy.

Question 20

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.

Answer 20

Highertemperaturewouldcausetherateof
nuclearfusiontorise,whichwouldincrease
theinternalpressure,causing thecoretoexpandandcooluntilthe fusionratereturnedtonormal.

Question 21

Whathappenstoenergyintheconvectionzoneof

theSun?

Answer 21

Energyistransportedoutwardbytherising

ofhotplasmaandthesinkingofcoolerplasma.

Question 22

Whatprocessesareinvolvedinthesunspot

cycle?

Answer 22

thewindingofmagneticfieldlinesdueto

differentialrotation

Question 23

Sinceallstarsbegintheirliveswiththesame
basiccomposition,whatcharacteristicmost
determineshowtheywilldiffer?

Answer 23

masstheyareformedwith

Question 24

Astar’sluminosityisthe

Answer 24

totalamountoflightthatthestarwill

radiateoveritsentirelifetime.

Question 25

Ifthedistancebetweenusandastaris
doubled,witheverythingelseremainingthe
same,theluminosity

Answer 25

remainsthesame,buttheapparent

brightnessisdecreasedbyafactoroffour.

Question 26

Supposethatyoumeasuretheparallax
angleforaparticularstartobe0.5arcsecod.
Thedistancetothisstaris

Answer 26

2parsecs.

Question 27

Whichofthefollowingstatementsaboutspectral
typesofstarsistrue?
A)AstarwithspectraltypeAiscoolerthana
starwithspectraltypeB.
B)Thespectraltypeofastarcanbeusedto
determineitssurfacetemperature.
C)Thespectraltypeofastarcanbeusedto
determineitscolor.
D)AstarwithspectraltypeF2ishotterthana
starwithspectraltypeF3.
E)Alloftheabovearetrue.

Answer 27

Alloftheabovearetrue.

Question 28

Supposeyouseetwomain-sequencestars
ofthesamespectraltype.Star1isdimmerin
apparentbrightnessthanStar2byafactorof100.
Whatcanyouconclude?(Neglectanyeffectsthatmight
becausedbyinterstellardustandgas.)

Answer 28

Star1is10timesmoredistantthanStar2.

Question 29

Whichofthefollowingtermsisgiventoapairofstarsthatwecandetermineareorbitingeachotheronlyby
measuringtheirperiodicDopplershifts?
A)doublestar
B)spectroscopicbinary
C)visualbinary
D)eclipsingbinary
E)noneoftheabove

Answer 29

spectroscopicbinary

Question 30

OnaHertzsprung-Russelldiagram,wherewouldwefind

starsthathavethelargestradii?

Answer 30

upperright

Question 31

Youobserveastarinthediskofthe
MilkyWay,andyouwanttoplotthestaron
anH-Rdiagram.Youwillneedto
determineallofthefollowing,exceptthe

Answer 31

rotationrateofthestar

Question 32

Whichofthefollowingistrueaboutlow­massstarscomparedtohigh­massstars?
A)Low massstarsarehotterandmore
luminousthanhigh­massstars.
B)Low ­massstarsarecoolerandless
luminousthanhigh­massstars.
C)Low ­massstarsarecoolerbutmore
luminousthanhigh­massstars.
D)Low massstarshavethesametemperature
andluminosityashigh­massstars.
E)Low massstarsarehotterbutless
luminousthanhigh­massstars.

Answer 32

Low­massstarsarecoolerand

lessluminousthanhigh­massstars.

Question 33

WhyareCepheidvariablessoimportant

formeasuringdistancesinastronomy?

Answer 33

Theirluminositycanbe

inferredfromtheirperiod.

Question 34

Clusteragescanbedeterminedfrom

Answer 34

mainsequenceturnoff.

Question 35

Thetypicaldensityandtemperatureof

molecularcloudsare

Answer 35

300moleculespercubic

centimeter,10­30Kelvin.

Question 36

Ifyouwantedtoobservestarsbehind
amolecularcloud,inwhatwavelength
oflightwouldyoumostlikely
observe?

Answer 36

infrared

Question 37

Thethermalpressureofagasdepends

on

Answer 37

densityandtemperature.

Question 38

Whatpreventsthepressurefrom
increasingasacloudcontracts
duetoitsgravity?

Answer 38

Excesspressureisreleasedin

jetsofmaterialfromtheyoungstars.

Question 39

Whatisthelikelyreasonthat
wecannotfindanyexamples
ofthefirstgenerationstars?

Answer 39

Thefirstgenerationstarswere

allverymassiveandexplodedassupernova.

Question 40

Whendoesastar

becomeamain­sequencestar?

Answer 40

whentherateofhydrogenfusionwithinthestar’scoreis

highenoughtomaintaingravitationalequilibrium

Question 41

Whichofthefollowingdiscoveries,
iftheyexisted,wouldnecessitate
areevaluationofourideasofstellar
formation?

Answer 41

a0.01­

solar­massstar

Question 42

Whatpreventsabrowndwarf

fromundergoingnuclearfusion?

Answer 42

Degeneracypressurehaltsthecontraction
ofaprotostarsothecoreneverbecomes
hotordenseenoughfornuclearfusion.