What is proper time?
a. Proper time is the time measured by a clock at rest with respect to the observer.
b. Proper time is time based on your actual longitude, not your time zone.
c. Proper time is the time given on your GPS.
d. Proper time means standard time as opposed to daylight savings time.
a
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Energy Levels: Radio astronomers often study the radiation emitted by a hydrogen atom from a transition between the two hyperfine levels associated with the ground state. This radiation has a wavelength of 21 cm. What is the energy difference between the hyperfine levels? (1 eV = 1.60 × 10-19 J)
A. 5.9 × 10-6 eV B. 5.9 × 10-25 J C. 1.7 × 10-24 J D. 4.7 × 10-25 J
What is a planetary nebula?
A) The bipolar jets ejected by a T Tauri variable B) A planet surrounded by a glowing shell of gas C) The disc of gas and dust surrounding a young star that will soon form a solar system D) The ejected envelope, often bipolar, of a red giant surrounding a stellar core remnant E) A type of young, medium mass star
Charge carriers in a metal are electrons rather than protons because electrons are
A) negative. B) smaller. C) loosely bound. D) none of the above
How does gravitational lensing tell us about the mass of a galaxy cluster?
A) The lensing broadens spectral lines, and we can use the broadening to "weigh" the cluster. B) Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it. C) The lensing allows us to determine the orbital speeds of galaxies in the cluster, so that we can determine the mass of the cluster from the orbital velocity law. D) Newton's universal law of gravitation predicts how mass can distort light, so we can apply Newton's law to determine the mass of the cluster.