Current: In an electroplating process, it is desired to deposit 40 mg of silver on a metal part by using a current of 2.0 A. How long must the current be allowed to run to deposit this much silver? The silver ions are singly charged, and the atomic mass of silver is 108 g/mol. (e = 1.60 × 10-19 C, NA = 6.02 × 1023 atoms/mol)
A. 16 s
B. 18 s
C. 20 s
D. 22 s
Answer: B
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Why isn’t the crust of Venus broken into mobile plates as Earth’s crust is? How do you know?
a. Venus’s crust is much thicker and denser than Earth’s, so that probably prevents the crust from breaking. Moreover, there are no shield volcanoes on Venus. b. The mantle of Venus consists of great amounts of sulfur and fluorine, which makes mantle substances more solid and less plastic. So there are no traces of magma eruptions on Venus. c. Strong winds in the dense atmosphere of Venus sufficiently get rid of the interior heat, so there are no interior currents of matter to drive plate motion. Moreover, there are no shield volcanoes on Venus. d. Low-density, dryness, and pliability of Venus’s crust probably prevented it from breaking into rigid plates. On Venus there are no chains of composite volcanoes that form at plate boundaries.
Applications to Astronomy: It can be shown that the approximate age of the universe is 1/H, where H is the Hubble constant. Taking H = 20 
, estimate the age of the universe, in years. (1 ly = 9.46 × 1015 m)
A. 15 thousand years B. 15 million years C. 15 billion years D. 50 billion years
Coulomb's Law: As shown in the figure, three charges are at corners of a rectangle. The charge in the bottom right corner is Q = - 90 nC, and all the other quantities are accurate to two significant figures. What is the magnitude of the net electrical force on Q due to the other two charges? (k = 1/4??0 = 9.0 × 109 N ? m2/C2) 
A. 3.8 × 10-2 N B. 2.8 × 10-2 N C. 5.3 × 10-2 N D. 7.1 × 10-2 N
The interior of a refrigerator has a volume of 0.600 m3. The temperature inside the refrigerator in 282 K, and the pressure is 101 kPa. If the molecular weight of air is 29 g/mol, what is the mass of air inside the refrigerator?
The ideal gas constant is R = 8.314 J/mol ? K = 0.0821 L ? atm/mol ? K. A) 500 g B) 560 g C) 140 g D) 270 g E) 750 g