Quantum Physics

Answers to Quick Quizzes, Odd-Numbered Conceptual Questions and Problems A.195. 1.7 10 6 N/C7. (a) 1.13 10 5 N/C (b) 1.80 10 14 N(c) 4.38 10 17 J9. (a) 0.500 m (b) 0.250 m11. (a) 1.44 10 7 V (b) 7.19 10 8 V13. (a) 2.67 10 6 V (b) 2.13 10 6 V15. (a) 103 V (b) 3.85 10 7 J; positive work must be doneto separate the charges.17. 11.0 kV19. 2.74 10 14 m21. 0.719 m, 1.44 m, 2.88 m. No. The equipotentials are notuniformly spaced. Instead, the radius of an equipotenial isinversely proportional to the potential.23. (a) 1.1 10 8 F (b) 27 C25. (a) 11.1 kV/m toward the negative plate (b) 3.74 pF(c) 74.7 pC and 74.7 pC27. (a) 90.4 V (b) 9.04 10 4 V/m29. (a) 13.3 C on each (b) 20.0 C, 40.0 C31. (a) 2.00 F (b) Q 3 24.0 C, Q 4 16.0 C,Q 2 8.00 C, (V ) 2 (V ) 4 4.00 V, (V ) 3 8.00 V33. (a) 5.96 F (b) Q 20 89.5 C, Q 6 63.2 C,Q 3 Q 15 26.3 C35. Q 1 16.0 C, Q 5 80.0 C, Q 8 64.0 C,Q 4 32.0 C37. (a) Q 25 1.25 mC, Q 40 2.00 mC (b) Q 25 288 C,Q 40 462 C, V 11.5 V39. Q 1 3.33 C, Q 2 6.67 C41. 83.6 C43. 2.55 10 11 J45. 3.2 10 10 J47. 4.049. (a) 8.13 nF (b) 2.40 kV51. (a) volume 9.09 10 16 m 3 , area 4.54 10 10 m 2(b) 2.01 10 13 F (c) 2.01 10 14 C,1.26 10 5 electronic charges55. 4.29 F57. 6.25 F59. 4.47 kV61. 0.75 mC on C 1 , 0.25 mC on C 265. 50 NChapter 17QUICK QUIZZES1. (d)2. (b)3. (c), (d)4. (b)5. (b)6. (a)7. (b)8. (a)CONCEPTUAL QUESTIONS1. Charge. Because an ampere is a unit of current (1 A 1 C/s) and an hour is a unit of time (1 h 3 600 s), then1A h 3 600 C.3. The gravitational force pulling the electron to the bottomof a piece of metal is much smaller than the electrical repulsionpushing the electrons apart. Thus, free electronsstay distributed throughout the metal. The concept ofcharges residing on the surface of a metal is true for ametal with an excess charge. The number of free electronsin an electrically neutral piece of metal is the same as thenumber of positive ions—the metal has zero net charge.5. A voltage is not something that “surges through” a completedcircuit. A voltage is a potential difference that is appliedacross a device or a circuit. It would be more correctto say “1 ampere of electricity surged through the victim’sbody.” Although this amount of current would have disastrousresults on the human body, a value of 1 (ampere)doesn’t sound as exciting for a newspaper article as 10 000(volts). Another possibility is to write “10 000 volts of electricitywere applied across the victim’s body,” which stilldoesn’t sound quite as exciting.7. We would conclude that the conductor is nonohmic.9. The shape, dimensions, and the resistivity affect the resistanceof a conductor. Because temperature and impuritiesaffect the conductor’s resistivity, these factors also affectresistance.11. The radius of wire B is the square root of three times theradius of wire A. Therefore the cross-sectional area of Bthree times larger than that of A.13. The drift velocity might increase steadily as time goes on,because collisions between electrons and atoms in thewire would be essentially nonexistent and the conductionelectrons would move with constant acceleration. The currentwould rise steadily without bound also, because I isproportional to the drift velocity.15. Once the switch is closed, the line voltage is applied acrossthe bulb. As the voltage is applied across the cold filamentwhen it is first turned on, the resistance of the filament islow, the current is high, and a relatively large amount ofpower is delivered to the bulb. As the filament warms, itsresistance rises and the current decreases. As a result, thepower delivered to the bulb decreases. The large currentspike at the beginning of the bulb’s operation is the reasonthat lightbulbs often fail just after they are turned on.PROBLEMS1. 3.00 10 20 electrons move past in the direction oppositeto the current.3. 2.00 C5. 1.05 mA7. 27 yr9. (a) n is unaffected (b) v d is doubled11. 32 V is 200 times larger than 0.16 V13. 0.17 mm15. (a) 30 (b) 4.7 10 4 m17. silver ( 1.59 10 8 m)19. 256 21. 1.98 A23. 26 mA25. (a) 5.89 10 2 (b) 5.45 10 2 27. (a) 3.0 A (b) 2.9 A29. (a) 1.2 (b) 8.0 10 4 (a 0.080% increase)31. 5.00 A, 24.0 33. 18 bulbs35. 11.2 min37. 34.4 39. 1.6 cm41. 295 metric tons/h43. 26 cents45. 23 cents47. $1.2