The stars in our sky twinkle in brightness and color because of
A) turbulence in the Earth's atmosphere.
B) rapid changes in the brightness and colors of stars caused by changes in their spectra.
C) light pollution.
D) the bubbling and boiling of gases on the surfaces of stars.
A) turbulence in the Earth's atmosphere.
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During each cycle of operation a refrigerator absorbs 45 cal from the freezer compartment and expels 85 cal to the room. If one cycle occurs every 8.0 s, how many minutes will it take to freeze 500 g of water, initially at 0°C? (Lv = 80 cal/g)
a. 800 min c. 120 min b. 4400 min d. 150 min
The velocity of shear waves in a long brass rod is 2,033 m/s. If the density of brass is 
then what is the shear modulus of brass?
A. 
B. 
C. 
D. 
E. 
A heavily loaded boat is floating in a pond. The boat starts to sink because of a leak but quick action plugging the leak stops the boat from going under although it is now deeper in the water. What happens to the surface level of the pond?
a. It stays the same. b. It goes up. c. It goes down. d. More information is needed to reach a conclusion.
How many photons per second emerge from a laser of power with wavelength (c = 3.00 × 108 m/s, h = 6.626 × 10-34 J ? s)
A) 6.09 × 1015 photons/s B) 5.03 × 1012 photons/s C) 3.07 × 1015 photons/s D) 3.07 × 1013 photons/s