What do we mean by fnow in the Drake equation
(Number of Civilizations = NHP × flife × fcivilization × fnow)?
A) the fraction of planets with civilizations on which the civilizations exist now
B) the fraction of time since the Big Bang represented by the present era
C) the fraction of all species ever to exist that we currently are aware of
D) the fraction of planets in the galaxy on which a civilization could theoretically develop now
E) the fraction of civilizations in the universe that currently are sending messages to us
A) the fraction of planets with civilizations on which the civilizations exist now
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The following objects are found in a spiral arm of a galaxy. Which is the exception?
a. population II stars b. OB associations c. emission nebulae d. population I stars e. clouds of gas and dust
Recall that Hubble's law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0 = 55 km/s/Mpc
How fast would a galaxy located 500 megaparsecs distant be receding from us? Show all work clearly, and state your final answer with a complete sentence. Give the speed in units of kilometers per second and as a percentage of the speed of light.
A flat coil of wire consisting of 20 turns, each with an area of 50 cm2, is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 2.0 T to 6.0 T in 2.0 s. If the coil has a total resistance of 0.40 ?, what is the magnitude of the induced current?
A. 0.70 A B. 0.60 A C. 0.50 A D. 0.80 A E. 0.20 A
When the voltage across a nonohmic resistor is doubled, the current through it triples. What happens to the power delivered to this resistor?
a. This cannot be answered with the information given. b. The power decreases to 2/3 of the original amount. c. The power increases to 1.5 times the original amount. d. The power increases to 6 times the original amount.