The cooling effect in a refrigerator is produced by _____
a. the electric motor which essentially converts electricity into heat
b. compression of the refrigeration gas into a liquid
c. liquefying the refrigeration gas
d. vaporization of the refrigeration liquid
e. proper insulation
d
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A typical galaxy is a
A) collection of millions or billions of stars, bound together by gravity and orbiting a common center. B) large, glowing ball of gas powered by nuclear energy. C) nearby object orbiting a planet. D) relatively small, icy object orbiting a star. E) system consisting of one or a few stars orbited by planets, moons, and smaller objects.
Which of the following explains why navigators prior to a few hundred years ago found it much more difficult to determine longitude than latitude?
A) Determining longitude requires an accurate clock, but latitude does not. B) Determining longitude requires mathematical techniques that were not known at the time. C) Determining longitude requires much more precise measurements of angles in the sky than does latitude. D) Determining longitude requires accurate tables of the celestial coordinates of stars, while determining latitude does not.
Astronaut Jill leaves Earth in a spaceship and is now traveling at a speed of 0.280c relative to an observer on Earth. When Jill left Earth, the spaceship was equipped with all kinds of scientific instruments, including a meter stick
Now that Jill is underway, how long does she measure the meter stick to be? A) 1.00 m B) 0.960 m C) 1.04 m D) 0.280 m E) 1.28 m
The spectra of the coolest stars contain strong absorption features (or lines) of
a. TiO molecules. b. ionized helium. c. helium. d. hydrogen. e. All of the other choices are correct.