The atmospheric carbon dioxide concentration
A) is higher than it has been at any time during the last 800,000 years
B) is higher than it has been at any time during the Earth's history
C) has remained roughly constant during the last 800,000 years
D) is lower than it has been at any time during the last 800,000 years
A
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The Hubble time is____
a. an estimate of the age of the Universe b. the time needed for a galaxy to travel 1 Mpc c. not connected to Hubble law of galactic redshifts d. the time for light to cross the Universe e. the time needed for galaxies to form
The Greeks abandoned their earliest cosmological theory (planets moving in simple circles around Earth) because
A) it did not agree with their observations of the planets.
B) it seemed messy and unsatisfying.
C) they came to believe that Earth should be at the center of things.
D) they came to believe that the sun should be at the center of things.
E) Actually, they never did abandon or revise their earliest theory--it was not altered until the time of Copernicus.
A high-voltage transmission line of diameter 2 cm and length 150 km carries a steady current of 1 000 A. If the conductor is copper with a free charge density of 8 × 10^28 electrons/m3, how long does it take one electron to travel the full length of the cable? (e = 1.6 × 10^?19 C)
a. 6.0 × 10^2 s b. 6.0 × 10^4 s c. 6.0 × 10^6 s d. 6.0 × 10^8 s e. 6.0 × 10^–10 s
If three identical bulbs are connected in series across a 12V battery, the voltage across each bulb will be
a. 12V b. 4V c. different d. none of the above