Deck 31: Physics in the 21st Century

Question 1

If a photon produces an electron-positron pair and one other particle, the other particle may be a(n):

A) photon.
B) antineutrino.
C) muon.
D) neutrino.

Answer 1

photon.

Question 2

Which of the following particles is made of two smaller particles?

A) electron
B) proton
C) photon
D) None of these choices.

Answer 2

None of these choices.

Question 3

The Dirac theory predicted that a positron would be:

A) a particle with same mass as an electron but with opposite charge.
B) a particle with negative mass.
C) a negative electron in a negative energy state.
D) All of the above.

Answer 3

a particle with same mass as an electron but with opposite charge.

Question 4

Baryons are composed of 3 quarks. If all 3-quark compositions of particles could happen, what would be the highest possible charge for such a particle?

A) There is no upper limit, though the charge is usually less than 3 e
B) 2 e
C) 1 e
D) 3 e

Question 5

According to present theories, there is a neutrino for all the following particles except:

A) the electron.
B) the tau lepton.
C) the muon.
D) the positive Kaon.

Question 6

A positron and an electron differ in:

A) spin.
B) charge.
C) mass.
D) energy.

Question 7

What following quantity is conserved in the following reaction: ?

A) charge
B) lepton number
C) baryon number
D) All of the above.

Question 8

If a K⁰ meson at rest decays in 0.90 *10 ^{- 10} s, how far will a K⁰ meson moving at 0.95c travel through a bubble chamber? (c = 3.00 *10⁸ m/s)

A) 2.6 cm
B) 8.2 cm
C) 9.3 cm
D) 13 cm

Question 9

Which of the following is not a meson?

A) the phi
B) the kaon
C) the pion
D) All of the above are mesons.

Question 10

Baryons are composed of _______ quarks, and mesons are composed of ________ quarks.

A) two, two
B) two, three
C) three, three
D) three, two

Question 11

If a muon at rest decays into an electron at rest according to , what is the total energy of the neutrinos?

A)
B) There is insufficient information since the neutrinos are different and have unknown masses, so the answer cannot be given at this time.
C)
D)

Question 12

A neutron and a proton have the same:

A) charge.
B) half-life.
C) baryon number.
D) mass.

Question 13

The exchange of mediating photons can produce:

A) neither a repulsive nor an attractive force.
B) either a repulsive or an attractive force.
C) a repulsive force.
D) an attractive force.

Question 14

A proton and antiproton each with total energy 800 GeV collide head-on. What is the total energy (particles + energy) released?

A) zero
B) 800 GeV
C) 400 GeV
D) 1600 GeV

Question 15

Which particle in the free state is least stable?

A) electron
B) neutron
C) photon
D) proton

Question 16

The size and sign of the charge on an electron is the same as that for:

A) an antiproton.
B) a positron.
C) an antineutron.
D) an antineutrino.

Question 17

Which, if any, is an elementary particle, i.e., not composed of other particles?

A) the particle
B) the neutron.
C) the electron
D) All three are not elementary particles.

Question 18

Which of the following is not conserved?

A) lepton number
B) meson number
C) baryon number
D) energy

Question 19

"MeV/c²" is a unit for:

A) energy.
B) nuclear force.
C) mass.
D) momentum.

Question 20

Which of these particles has the least mass?

A) electron neutrino
B) muon
C) electron
D) pion

Question 21

Theoretical physicists have had the greatest success in combining which force with the weak nuclear force?

A) gravitational force
B) electromagnetic force
C) strong nuclear force
D) the force caused by the exchange of gluons

Question 22

The microwave background radiation:

A) represents the leftover glow from the Big Bang.
B) had its slight non-uniformity measured by COBE.
C) was discovered by Penzias and Wilson.
D) All of the above.

Question 23

The constituent quarks of the proton are uud. What are the charges on u and d?

A)
B)
C)
D)

Question 24

Of the quarks u, d, c, s, t, and b, which have positive fractional electronic charge?

A) u, d, c
B) d, s, b
C) s, t, b
D) u, c, t

Question 25

Which of the following particles has not been observed experimentally?

A) antiproton
B) graviton
C) photon
D) Z⁰ boson

Question 26

Which of the following forces is the strongest at near distances?

A) gravitational
B) weak nuclear
C) strong nuclear
D) electromagnetic

Question 27

Processes in which one type of quark is converted into another type of quark involve which force?

A) electromagnetic
B) strong force
C) weak force
D) gravitational

Question 28

The strong force is mediated by:

A) the gluon.
B) the W^- boson.
C) the W⁺ boson.
D) All of these choices.

Question 29

Which force can act over distances comparable to the distance between planets?

A) only electrical
B) only gravitational
C) only magnetic
D) All of these choices.

Question 30

Assuming the Hubble constant is (21 km/s)/(10⁶ ly), what is the recession speed of a galaxy 300 million parsecs away? (1 parsec = 3.26 ly)

A) 4200 km/s
B) 21,000 km/s
C) 640 km/s
D) 7000 km/s

Question 31

The cosmic background radiation appears compatible with a blackbody source at what temperature?

A) 0.0003 K
B) 3 K
C) 300 K
D) 0.03 K

Question 32

Of the following mesons, which is its own antiparticle?

A)
B)
C)
D) none of those given

Question 33

The weak force that acts between an electron and a quark is caused by the exchange of:

A) photons.
B) W⁺, W^-, or Z⁰ bosons.
C) gravitons.
D) gluons.

Question 34

The quark structure of the neutron is udd. What is the quark structure of the antineutron?

A)
B) ddu
C)
D) udd, since the neutron is its own antiparticle

Question 35

The following reaction can occur by the strong interaction: $\pi$ ⁰ + n $\rightarrow$ K⁺ + $\Sigma$ ^-. If the quark composition of the n is (udd), the $\pi$ ⁰ is and the composition of the K⁺ is , what is the quark composition of the $\Sigma$ ^-?

A) uds
B) dds
C) sss
D)