1. Q44.1 The strong nuclear force has a short range compared to the electromagnetic force. Why is this? 1. the particles that mediate the strong force are charged, while those that mediate the electromagnetic force are neutral 2. the particles that mediate the strong force are massive, while those that mediate the electromagnetic force are massless 3. the particles that mediate the strong force have spin 0, while those that mediate the electromagnetic force have spin 1 4. all of 1., 2., and 3. 5. none of 1., 2., or 3.

2. A44.1 The strong nuclear force has a short range compared to the electromagnetic force. Why is this? 1. the particles that mediate the strong force are charged, while those that mediate the electromagnetic force are neutral 2. the particles that mediate the strong force are massive, while those that mediate the electromagnetic force are massless 3. the particles that mediate the strong force have spin 0, while those that mediate the electromagnetic force have spin 1 4. all of 1., 2., and 3. 5. none of 1., 2., or 3.

3. Q44.2 What is the advantage of using colliding beams in particle physics experiments? 1. the available energy is larger 2. the reaction products are always produced at rest, so they can be studied at leisure 3. there are fewer problems with the apparatus becoming radioactive 4. both 1. and 2. 5. all of 1., 2., or 3.

4. A44.2 What is the advantage of using colliding beams in particle physics experiments? 1. the available energy is larger 2. the reaction products are always produced at rest, so they can be studied at leisure 3. there are fewer problems with the apparatus becoming radioactive 4. both 1. and 2. 5. all of 1., 2., or 3.

5. Q44.3 Which of the following properties is not conserved in certain particle physics experiments? 1. baryon number 2. lepton number 3. strangeness 4. electric charge 5. in fact, all of these quantities are always conserved

6. A44.3 Which of the following properties is not conserved in certain particle physics experiments? 1. baryon number 2. lepton number 3. strangeness 4. electric charge 5. in fact, all of these quantities are always conserved

7. Q44.4 A baryon called the  ++ is comprised of three u quarks, each of which has the same spin component. How can the existence of this baryon be explained in light of the Pauli exclusion principle, which forbids more than one fermion from being in the same quantum-mechanical state? 1. quarks are not fermions, so the Pauli exclusion principle doesn’t apply 2. quarks have an additional property called color, and each quark has a different color 3. the quarks within the  ++ are continually being created and annihilated, so no more than one quark has the same spin component at any given instant 4. baryons continuously produce virtual mesons which carry off any quarks that try to get into an already occupied state

8. A44.4 A baryon called the  ++ is comprised of three u quarks, each of which has the same spin component. How can the existence of this baryon be explained in light of the Pauli exclusion principle, which forbids more than one fermion from being in the same quantum-mechanical state? 1. quarks are not fermions, so the Pauli exclusion principle doesn’t apply 2. quarks have an additional property called color, and each quark has a different color 3. the quarks within the  ++ are continually being created and annihilated, so no more than one quark has the same spin component at any given instant 4. baryons continuously produce virtual mesons which carry off any quarks that try to get into an already occupied state

9. Q44.5 What causes the very large redshifts of extremely distant galaxies? 1. the Doppler effect 2. the stretching of light waves as they traverse an expanding universe 3. the cooling-off of the expanding universe 4. differences between the kinds of stars that existed in the distant past and those that exist today 5. a gravitational effect related to photons climbing out of the strong gravity of a distant galaxy

10. A44.5 What causes the very large redshifts of extremely distant galaxies? 1. the Doppler effect 2. the stretching of light waves as they traverse an expanding universe 3. the cooling-off of the expanding universe 4. differences between the kinds of stars that existed in the distant past and those that exist today 5. a gravitational effect related to photons climbing out of the strong gravity of a distant galaxy

11. Q44.6 The dominant contribution to the average energy density of the universe comes from 1. the rest energy of baryons 2. the rest energy of dark matter 3. dark energy 4. present-day observations cannot yet answer this question

12. A44.6 The dominant contribution to the average energy density of the universe comes from 1. the rest energy of baryons 2. the rest energy of dark matter 3. dark energy 4. present-day observations cannot yet answer this question

13. Q44.7 Prior to the appearance of the first stars, the chemical composition of the universe was 1. 75% hydrogen and 25% helium by mass 2. 50% hydrogen and 50% helium by mass 3. 25% hydrogen and 75% helium by mass 4. essentially 100% hydrogen

14. A44.7 Prior to the appearance of the first stars, the chemical composition of the universe was 1. 75% hydrogen and 25% helium by mass 2. 50% hydrogen and 50% helium by mass 3. 25% hydrogen and 75% helium by mass 4. essentially 100% hydrogen

15. Q44.8 We cannot detect photons emitted earlier than about 380,000 years after the Big Bang. Why not? 1. there were no atoms before this time, so there were no transitions between atomic energy levels and hence no photon emission 2. there were no atoms before this time and the universe was opaque 3. there were no nuclei before this time, only baryons and electrons, so the universe was opaque 4. there were no photons before this time, only baryons and electrons

16. A44.8 We cannot detect photons emitted earlier than about 380,000 years after the Big Bang. Why not? 1. there were no atoms before this time, so there were no transitions between atomic energy levels and hence no photon emission 2. there were no atoms before this time and the universe was opaque 3. there were no nuclei before this time, only baryons and electrons, so the universe was opaque 4. there were no photons before this time, only baryons and electrons