Deck 44: Particle Physics and Cosmology

Question 1

Consider the decay π⁺ → μ⁺ + γ.This decay is

A) allowed.
B) forbidden because conservation of energy is violated.
C) forbidden because conservation of baryon number is violated.
D) forbidden because conservation of mass is violated.
E) forbidden because conservation of lepton numbers is violated.

Answer 1

forbidden because conservation of lepton numbers is violated.

Question 2

Consider the decay π^o → μ^- + e⁺.This decay is

A) allowed.
B) forbidden because conservation of energy is violated.
C) forbidden because conservation of baryon number is violated.
D) forbidden because conservation of mass is violated.
E) forbidden because conservation of lepton numbers is violated.

Answer 2

forbidden because conservation of lepton numbers is violated.

Question 3

How many different kinds of leptons are known to exist,including antiparticles as different kinds?

A) 4
B) 6
C) 8
D) 2
E) 12

Answer 3

12

Question 4

Which of the following particles are leptons? (There may be more than one correct choice.)

A) positron
B) muon
C) π-meson
D) neutron
E) electron

Question 5

Composite particles that are composed of a quark and antiquark pair are called

A) leptons.
B) hadrons.
C) mesons.
D) nucleons.
E) baryons.

Question 6

What type of particle is a neutron? (There may be more than one correct choice.)

A) lepton
B) meson
C) baryon
D) nucleon
E) hadron

Question 7

Which of the following particles is NOT made up of quarks? (There may be more than one correct choice.)

A) proton
B) neutron
C) electron
D) π-meson
E) neutrino

Question 8

The cosmic background radiation corresponds to a temperature of about

A) 1.4 K.
B) 2.7 K.
C) 3.8 K.
D) 4.9 K.
E) 5.5 K.

Question 9

The decay n → p⁺ + e^- + γ does NOT occur because it would violate conservation of

A) baryon number.
B) lepton number.
C) charge.
D) energy.

Question 10

Particles that do not interact via the strong force but do interact via the weak nuclear force (and presumably by the much weaker gravitation force)are called

A) baryons.
B) mesons.
C) hadrons.
D) leptons.
E) nucleons.

Question 11

What type of particle is a proton? (There may be more than one correct choice.)

A) lepton
B) meson
C) baryon
D) nucleon
E) hadron

Question 12

What type of particle is an electron? (There may be more than one correct choice.)

A) lepton
B) meson
C) baryon
D) nucleon
E) hadron

Question 13

Composite particles that are composed of three quarks are called

A) leptons.
B) hadrons.
C) mesons.
D) bosons.
E) baryons.

Question 14

What is the quark composition of the proton?

A) u d
B) uud
C) udd
D) u
E) u d

Question 15

The reaction p + → e⁺ + γ is NOT possible because

A) baryon number is not conserved.
B) lepton number is not conserved.
C) charge is not conserved.
D) energy is not conserved.
E) This reaction IS possible.

Question 16

Consider the possibility that a neutron could decay into a proton and a pion.What,if any,of the following conservation laws would this process violate?

A) conservation of energy
B) conservation of lepton number
C) conservation of charge
D) conservation of baryon number
E) None of the above laws would be violated.

Question 17

Hadrons are divided into two subgroups called

A) baryons and leptons.
B) leptons and mesons.
C) mesons and baryons.
D) nucleons and leptons.
E) mesons and leptons.

Question 18

The reaction p + e^- → + e⁺ is not possible because

A) baryon number is not conserved.
B) lepton number is not conserved.
C) charge is not conserved.
D) energy is not conserved.
E) This reaction IS possible.

Question 19

Which of the following particles are made up of quarks? (There may be more than one correct choice.)

A) nucleons
B) hadrons
C) neutrinos
D) muons
E) mesons

Question 20

Given that the reaction n + π⁺ → p can occur and that the quark composition of the neutron is udd and that of the proton is uud,what must be the quark composition of the π⁺ meson?

A) u
B) d
C) d
D) u
E) d

Question 21

A neutral η⁰ (having mass 0.642 u)that is at rest decays into two gamma ray photons.What is the energy in MeV of each photon? (1 u = 931.5 MeV/c²)

A) 299 MeV
B) 597 MeV
C) 1190 MeV
D) 199 MeV
E) 149 MeV

Question 22

The Large Hadron Collider (LHC)near Geneva,Switzerland is an example of a

A) linear accelerator.
B) cyclotron.
C) synchrotron.
D) None of the above

Question 23

What type of particle accelerator has two large D-shaped electrodes with a small gap between them,through which an alternating potential difference accelerates the particles in a constant magnetic field?

A) linear accelerator
B) cyclotron
C) synchrotron
D) None of the above

Question 24

The universe first became transparent to most light,coinciding with the origin of the cosmic background radiation,when the universe cooled enough to allow the formation of

A) protons and neutrons.
B) atomic nuclei.
C) neutral atoms.
D) stars and galaxies.

Question 25

Dark energy accounts for what percent of the known energy in the universe?

A) 8%
B) 24%
C) 68%
D) 94%

Question 26

Is the decay π⁰ → μ⁺ + v_μ allowed?

A) Yes, because it conserves energy.
B) No, because charge is not conserved.
C) No, because mass is created.
D) No, because lepton number is not conserved.

Question 27

A deuteron has the same charge as a proton but approximately twice the proton mass.Suppose deuterons are being accelerated in a cyclotron in an orbit of radius 75 cm at a frequency of 8.0 MHz.What magnetic field magnitude is needed? ,

A) 0.011 T
B) 0.11 T
C) 1.1 T
D) 11 T
E) 110 T

Question 28

Dark energy was discovered as astronomers studied

A) black holes.
B) redshift of distant galaxies.
C) the motion of galaxies within galactic clusters.
D) weakly interacting massive particles.

Question 29

A cyclotron is designed with a magnet that produces a magnetic field of 1.2 T.When refurbished,the magnet is replaced by one that produces a 1.5-T field.How does the maximum kinetic energy achieved by the protons change compared to their previous maximum kinetic energy?

A) It increases by 25%.
B) It decreases by 25%.
C) It increases by 56%.
D) It decreases by 56%.
E) It does not change.

Question 30

Dark matter was initially proposed to explain

A) black holes.
B) stellar nebulae.
C) the expansion of the universe.
D) the velocities of stars and gases in spiral galaxy arms.

Question 31

Suppose you were to try to create a proton-antiproton pair by annihilation of two very high-energy gamma rays of the same wavelength heading toward each other.The proton and the anti-proton have the same masses,but opposite charges.What would be the minimum energy needed for each photon? (e = 1.60 × 10^-19 C,m_proton = 1.67 × 10^-27 kg,

A) 1.022 MeV
B) 12.2 MeV
C) 1880 MeV
D) 939 MeV
E) 223 MeV

Question 32

A cyclotron of radius 0.25 m accelerates protons in a 1.7-T magnetic field.What is the frequency for the applied alternating voltage? (m_proton = 1.67 × 10^-27 kg,

A) 0.26 MHz
B) 2.6 MHz
C) 26 MHz
D) 260 MHz
E) 2600 MHz

Question 33

If the density of the universe is less than the critical density,then the total energy of the universe is

A) positive.
B) negative.
C) zero.

Question 34

Which one of the following processes CANNOT occur?

A) π⁺ → μ⁺ + v_μ
B) π⁰ → 2γ
C) π⁺ + p → K⁺ + Σ⁺
D) π^- + p → n + γ
E) Σ^- → π^- + p

Question 35

Which one of the following decays CAN occur?

A) π⁺ → μ⁺ + v_μ
B) p + n → p + p +
C) K⁺ → π⁰
D) μ^- → e^- + v_e + v_μ
E) K⁺ → 2π⁰

Question 36

Is the decay Σ⁺ → p + π⁺ allowed?

A) Yes, because it conserves energy.
B) No, because charge is not conserved.
C) No, because mass is created.
D) No, because lepton number is not conserved.

Question 37

The voltage across the dees of a cyclotron is 30,000 V.How many revolutions do the protons go through in reaching a kinetic energy of 21 MeV? (1 eV = 1.60 × 10^-19 J, ,m_proton = 1.67 × 10^-27 kg)

A) 2.0 million
B) 1400
C) 700
D) 350
E) 35

Question 38

Luminous (normal)matter makes up approximately what percentage of the known matter in the universe?

A) 5%
B) 15%
C) 60%
D) 95%

Question 39

How long after the Big Bang did nucleosynthesis,the combining of protons and neutrons together to form nuclei,begin to occur?

A) 10^-2 seconds
B) 3 minutes
C) 5000 years
D) 10⁹ years

Question 40

A cyclotron of radius 0.25 m accelerates nonrelativistic protons in a 1.7-T magnetic field.What is the kinetic energy of the protons when they leave the cyclotron? , ,m_proton = 1.67 × 10^-27 kg)

A) 3.7 MeV
B) 7.8 keV
C) 8.7 keV
D) 7.8 MeV
E) 8.7 MeV

Question 41

Consider the negative pion,π^-.
(a)What combination of up and down quarks makes up this particle?
(b)Is the π^- a baryon or a meson?
(c)Is the π^- a lepton or a hadron?

Question 42

If the Hubble constant is 25 km/s per million light-years,use it to estimate the age of the universe? (c = 3.00 × 10⁸ m/s,1 ly = 9.461 × 10¹⁵ m,1 y = 3.156 × 10⁷ s)

A) 10 Gy
B) 12 Gy
C) 15 Gy
D) 20 Gy
E) 25 Gy

Question 43

The H_α spectral line of hydrogen has a wavelength of 656.3 nm as measured in the laboratory.The H_α spectral line is observed in light from a distant star at a redshifted wavelength of 789.0 nm.If Hubble's law is valid for this star,estimate how far is it from Earth if the Hubble constant is 22 km/s per million light-years.(c = 3.00 × 10⁸ m/s, 1 ly=9.461 x 1015 m , 1 y = 3.156 × 10⁷ s)

A) 2.5 × 10⁹ ly
B) 9.1 × 10⁸ ly
C) 2.7 × 10⁸ ly
D) 9.1 × 10⁷ ly
E) 2.7 × 10⁷ ly

Question 44

Estimate the speed of a galaxy away from us if it is 10 billion light-years from us and if the Hubble constant is 22 km/s per million light-years.(c = 3.00 × 10⁸ m/s, , 1 y = 3.156 × 10⁷ s)

A) 0.1c
B) 0.3c
C) 0.5c
D) 0.7c
E) 0.9c

Question 45

A giant star in another galaxy exploded 67 million years ago,forming a supernova.The event is observed by an astronomer on Earth.Estimate the speed at which the supernova (and its galaxy)recedes from Earth if the Hubble constant is 22 km/s per million light-years. ,1 ly = 9.461 × 10¹⁵ m,1 y = 3.156 × 10⁷ s)

A) 1200 km/s
B) 670 km/s
C) 1500 km/s
D) 2700 km/s
E) 4700 km/s

Question 46

Redshift measurements on a galaxy show that it is receding from us with a velocity of 7240 km/s.Estimate how far away the galaxy is if the Hubble constant is 22 km/s per million light-years.(c = 3.00 × 10⁸ m/s,1 ly = 9.461 × 10¹⁵ m,1 y = 3.156 × 10⁷ s)

A) 3.1 × 10²⁴ m
B) 1.2 × 10²⁶ m
C) 1.2 × 10²⁴ m
D) 4.1 × 10²³ m
E) 2.0 × 10²² m

Question 47

A galaxy is observed receding from Earth with a speed of 2800 km/s.If the Hubble constant is 22 km/s per million light-years,estimate how many years ago the light that we presently see from the galaxy actually left the galaxy.(c = 3.00 × 10⁸ m/s,1 ly = 9.461 × 10¹⁵ m,

A) 1.3 × 10⁸ y
B) 4.2 × 10⁸ y
C) 4.2 × 10⁷ y
D) 1.4 × 10⁷ y
E) 4.2 × 10⁶ y

Question 48

Suppose that the Hubble constant had the value 35.0 km/s per million light-years. (1y=3.156 x 10⁷s ,m_h ≈ m_proton = 1.67 × 10^-27 kg,c = 3.00 × 10⁸ m/s, 1 light-year =9.461 x 10¹⁵ m,G = 6.67 × 10^-11 N ∙ m²/kg²)
(a)What would be the maximum density the universe could have that would still allow it to expand forever?
(b)Under the conditions of part (a),how many hydrogen atoms would we expect to find,on the average,in a volume of space measuring 3.00 m by 8.00 m by 8.00 m?

Question 49

A distant galaxy is emitting light from the helium spectrum at 388.9 nm.On Earth the wavelength of the light from this galaxy is measured to be 540.6 nm.Estimate how far from Earth (in light-years)this galaxy is if the Hubble constant has the value 22 km/s per million light-years. (c = 3.00 × 10⁸ m/s,1 ly = 9.461 × 10¹⁵ m,1 y = 3.156 × 10⁷ s)

Question 50

A galaxy is observed receding from Earth with a speed of 9800 km/s.A redshifted spectral line originating in the galaxy is compared to the same spectral line originating in the laboratory.If Hubble's law is valid for this galaxy,what is the ratio of the wavelength of the redshifted line to that of the unshifted line if the Hubble constant is 22 km/s per million light-years? (c = 3.00 × 10⁸ m/s,1 ly = 9.461 × 10¹⁵ m,1 y = 3.156 × 10⁷ s)

A) 1.033
B) 1.052
C) 1.072
D) 1.091
E) 1.130

Question 51

The background microwave radiation,discovered in 1965 by Penzias and Wilson,has its peak intensity at a wavelength of 1.06 mm.What blackbody temperature does this wavelength imply for the universe? (σ = 5.670 × 10^-8 W/m² • K⁴,Wien displacement law constant is 2.90 × 10^-3 m • K)

A) 2.7°C
B) -270°C
C) 0.0027 K
D) 0.00°C
E) -2.7°C

Question 52

How many quarks are in a deuteron,²H?

A) 1
B) 2
C) 3
D) 4
E) 6

Question 53

If a galaxy is moving away from us at 1.0% of the speed of light,use Hubble's law to estimate how far away it is from us if the Hubble constant is 22 km/s per million light-years. ,1 ly = 9.461 × 10¹⁵ m,1 y = 3.156 × 10⁷ s)

A) 14 ly
B) 140 ly
C) 140 thousand ly
D) 140 million ly
E) 140 billion ly

Question 54

If a galaxy is receding from us at 0.10c.Use Hubble's law to estimate the distance to this galaxy if the Hubble constant is 22 km/s per million light-years.(c = 3.00 × 10⁸ m/s, ,1 y = 3.156 × 10⁷ s)

A) 1.4 × 10⁹ ly
B) 6.6 × 10⁵ ly
C) 6.6 × 10⁵ Mly
D) 2.2 Mly
E) 1.4 × 10⁷ Mly