This figure shows an all-sky map of the cosmic microwave background recorded by the Planck telescope. How long did this light travel through space before it reached the telescope?
A) about 14 billion years
B) about 380,000 years
C) about a million years
D) Depending on what portion of the map we're looking at, the light traveled for times between just a few minutes and a few billion years.
A) about 14 billion years
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Will a blackbody at temperature T emit more photons per second with energy kBT or with energy 6 kBT?
A. It will emit more photons with the lower energy. B. It will emit more photons with the higher energy. C. The number of photons emitted will be the same. D. One has no way of telling.
Pumped storage facilities ________
a. increase the overall efficiency of a power plant b. make use of the output of electricity from photovoltaic cells c. are used to produce electricity mainly at night d. have an increase in their potential energy mainly at night e. cannot be used with a nuclear plant
Two concentric imaginary spherical surfaces of radius R and 2R respectively surround a positive point charge ?Q located at the center of the surfaces. When compared to the electric flux ?1 through the surface of radius R, the electric flux ?2 through the surface of radius 2R is
A.
.B.
.C.
D.
E.
What is the primary way in which we determine the mass distribution of a spiral galaxy?
A) We count the number of stars we can see at different distances from the galaxy's center. B) We calculate its mass-to-light ratio. C) We apply Newton's version of Kepler's third law to the orbits of globular clusters in the galaxy's halo. D) We construct its rotation curve by measuring Doppler shifts from gas clouds at different distances from the galaxy's center.