During the first moments of the big bang when elements could be created, nuclear fusion reactions made few heavy elements because
a. all heavy nuclei are unstable.
b. no stable nuclei exist with masses of 5 or 8 hydrogen masses.
c. the helium nucleus is unstable.
d. the temperature and density were too low.
e. no nuclei heavier than helium could form since there weren't any electrons formed.
b
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A proton is accelerated from rest through a potential difference of 150 V. It then enters a region of uniform magnetic field and moves in a circular path (radius = 12 cm). What is the magnitude of the magnetic field in this region?
a. 18 mT b. 12 mT c. 15 mT d. 22 mT e. 10 mT
Two thermometers are calibrated, one in degrees Celsius and the other in degrees Fahrenheit. At what temperature (in kelvins) do their readings measure the same temperature?
a. 218.15 b. 233.15 c. 273.15 d. 40.15 e. 0
Spectral lines take the shape of vertical lines because
A) the light is vertically polarized. B) they are images of a vertical slit. C) the energy levels in the atom are parallel to one another. D) all of the above E) none of the above
The 1420 MHz (21 cm) radio line generated by neutral hydrogen atoms is a good choice for interstellar communications because
A) it is the easiest radio frequency to generate B) it is the only radio frequency that is not blocked by interstellar matter C) all intelligent civilizations should be aware of its universal significance and would probably also think of sending and receiving signals at this frequency D) it is the only frequency to which radio telescopes can be tuned