Chapter 44: Q25P (page 1364)
The quark makeups of the proton and neutron are and,respectively. What are the quark makeups of (a) the antiproton and (b) the antineutron?
(a) The antiproton is written as.
(b) The antineutron is written as.
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Question: Due to the presence everywhere of the cosmic background radiation, the minimum possible temperature of a gas in interstellar or intergalactic space is not 0 K but 2.7 K. This implies that a significant fraction of the molecules in space that can be in a low-level excited state may, in fact, be so. Subsequent de-excitation would lead to the emission of radiation that could be detected. Consider a (hypothetical) molecule with just one possible excited state. (a) What would the excitation energy have to be for 25% of the molecules to be in the excited state? (Hint: See Eq. 40-29.) (b) What would be the wavelength of the photon emitted in a transition back to the ground state?
The rest energy of many short-lived particles cannot be measured directly but must be inferred from the measured momenta and known rest energies of the decay products. Consider the meson, which decays by the reaction. Calculate the rest energy of the meson given that the oppositely directed momenta of the created pions each have a magnitude 358.3 MeV. See Table 44-4 for the rest energies of the pions.
Will the universe continue to expand forever? To attack this question, assume that the theory of dark energy is in error and that the recessional speed of a galaxy a distance from us is determined only by the gravitational interaction of the matter that lies inside a sphere of radius centered on us. If the total mass inside this sphere in,the escape speed from the sphere is (Eq.13.28).(a) Show that to prevent unlimited expansion, the average density inside the sphere must be at least equal to
.
(b) Evaluate this “critical density” numerically; express your answer in terms of hydrogen atoms per cubic meter. Measurements of the actual density are difficult and are complicated by the presence of dark matter
There is no known meson with charge quantum number and strangeness or with and .Explain why in terms of the quark model.
Because of the cosmological expansion, a particular emission from a distant galaxy has a wavelength that is times the wavelength that emission would have in a laboratory. Assuming that Hubble’s law holds and that we can apply Doppler-shift calculations, what was the distance ()to that galaxy when the light was emitted?
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