Chapter 34: Q13CQ (page 1237)
Does observed gravitational lensing correspond to a converging or diverging lens? Explain briefly.
Gravitational lensing corresponds to a converging lens.
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For experimental evidence, particularly of previously unobserved phenomena, to be taken seriously it must be reproducible or of sufficiently high quality that a single observation is meaningful. Supernovais not reproducible. How do we know observations of it were valid? The fifth force is not broadly accepted. Is this due to lack of reproducibility or poor-quality experiments (or both)? Discuss why forefront experiments are more subject to observational problems than those involving established phenomena.
Must a complex system be adaptive to be of interest in the field of complexity? Give an example to support your answer.
(a) Calculate the approximate age of the universe from the average value of the Hubble constant,\({{\rm{H}}_{\rm{0}}}{\rm{ = 20km/s}} \cdot {\rm{Mly}}\). To do this, calculate the time it would take to travel\({\rm{1 Mly}}\)at a constant expansion rate of\({\rm{20 km/s}}\). (b) If deceleration is taken into account, would the actual age of the universe be greater or less than that found here? Explain.
(a) Estimate the mass of the luminous matter in the known universe, given there are\({\rm{1}}{{\rm{0}}^{{\rm{11}}}}\)galaxies, each containing\({\rm{1}}{{\rm{0}}^{{\rm{11}}}}\)stars of average mass\({\rm{1}}{\rm{.5}}\)times that of our Sun. (b) How many protons (the most abundant nuclide) are there in this mass? (c) Estimate the total number of particles in the observable universe by multiplying the answer to (b) by two, since there is an electron for each proton, and then by\({\rm{1}}{{\rm{0}}^{\rm{9}}}\), since there are far more particles (such as photons and neutrinos) in space than in luminous matter.
Not only is liquid nitrogen a cheaper coolant than liquid helium, its boiling point is higher (\({\rm{77 K}}\)vs\({\rm{4}}{\rm{.2 K}}\)). How does higher temperature help lower the cost of cooling a material? Explain in terms of the rate of heat transfer being related to the temperature difference between the sample and its surroundings.
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