Why did the era of nuclei end when the universe was about 380,000 years old?
A) The nucleosynthesis era that produced the nuclei heavier than helium ended.
B) Photons were finally able to escape the plasma of the early universe and were no longer available to produce hydrogen and helium nuclei.
C) Atomic nuclei were finally able to escape the plasma of the early universe.
D) The universe had expanded and cooled enough for stable, neutral atoms to form.
E) All the free particles had combined to form the nuclei of atoms.
D
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The chromosphere is often marked by eruptions on the solar surface called ____
a. solar flares b. prominences c. solar nodes d. diamond rings e. coronal mass ejections
What causes the sun to "bob" up-and-down in its orbit around the galactic center?
A) gravitational attraction towards other nearby galaxies B) the localized pull of stars within the disk itself C) lack of friction with the low-density interstellar medium D) A and B E) B and C
Suppose the pressure of 20 g of an ideal monatomic gas is tripled while its volume is halved. What happens to the internal energy of the gas?
a. It stays the same, as the described changes do not involve internal energy. b. It increases. c. It decreases. d. This depends on the molecular weight of the gas involved, thus this is indeterminate.
Which of the following is true of a light-year(ly)?
A) It is a unit of time. B) It is a unit of mass. C) It is a smaller unit of distance than kilometers. D) It is a larger unit of distance than the astronomical unit.