What is the primary reason why a star of twice the mass of the Sun is considered an unlikely candidate for finding an extraterrestrial civilization?
A. It is too hot and emits too much ultraviolet radiation.
B. The star's gravity is too strong.
C. Its main-sequence lifetime is too short.
D. High-mass stars produce only high-mass planets.
Ans: C. Its main-sequence lifetime is too short.
Explanation: Intelligent life took 3.5 to 4.0 billion years to develop on Earth. If this is typical, then any star more massive than about 1.5 solar masses would burn out or explode as a supernova before intelligent life developed on any planet orbiting the star. Section: The Drake equation: How many civilizations are likely to exist in the Milky Way?
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An element that is malleable, ductile, and a good conductor of heat and electricity would be classified as a
a. metalloid. b. semimetal. c. metal. d. nonmetal.
The primary mirror in an astronomical telescope must be a
a. half-silvered mirror b. convex mirror c. concave mirror d. plane mirror.
A double-star system with each star having the mass of the Sun has an orbital period of 1 year. A second double star system, also with each star having the mass of the Sun, has an orbital period of 8 years. If the separation of the stars in the first system is d and the orbits in both cases are circular, what is the separation of the stars in the second system?
a. 0.5d b. 2d c. 4d d. 8d
A parallel circuit consists of a 100-V DC power source, a 100-? resistor, and a variable resistor of resistance R, which varies from 0 to 100 ?. The current in the circuit is
?
?
a.
directly proportional to R.
b.
inversely proportional to R.
c.
directly proportional to (100 ? + R).
d.
inversely proportional to (100 ? + R).
e.
neither directly nor inversely proportional to R or to (100 ? + R).