College Physics for AP® Courses

# Chapter 20

1.

0.278 mA

3.

0.250 A

5.

1.50ms

7.

(a) $1.67 kΩ1.67 kΩ size 12{1 "." "67"" k" %OMEGA } {}$

(b) If a 50 times larger resistance existed, keeping the current about the same, the power would be increased by a factor of about 50 (based on the equation $P=I2RP=I2R size 12{P = I rSup { size 8{2} } R} {}$), causing much more energy to be transferred to the skin, which could cause serious burns. The gel used reduces the resistance, and therefore reduces the power transferred to the skin.

9.

(a) 0.120 C

(b) $7.50×1017 electrons7.50×1017 electrons size 12{7 "." "50"´"10" rSup { size 8{"17"} } " electrons"} {}$

11.

96.3 s

13.

(a) $7.81 × 10 14 He ++ nuclei/s 7.81 × 10 14 He ++ nuclei/s$

(b) $4.00 × 10 3 s 4.00 × 10 3 s$

(c) $7.71 × 10 8 s 7.71 × 10 8 s$

15.

$− 1 . 13 × 10 − 4 m/s − 1 . 13 × 10 − 4 m/s size 12{-1 "." "13"´"10" rSup { size 8{-4} } " m/s"} {}$

17.

$9 . 42 × 10 13 electrons 9 . 42 × 10 13 electrons size 12{9 "." "42"´"10" rSup { size 8{"13"} } " electrons"} {}$

18.

0.833 A

20.

$7 . 33 × 10 − 2 Ω 7 . 33 × 10 − 2 Ω size 12{7 "." "33"´"10" rSup { size 8{-2} } %OMEGA } {}$

22.

(a) 0.300 V

(b) 1.50 V

(c) The voltage supplied to whatever appliance is being used is reduced because the total voltage drop from the wall to the final output of the appliance is fixed. Thus, if the voltage drop across the extension cord is large, the voltage drop across the appliance is significantly decreased, so the power output by the appliance can be significantly decreased, reducing the ability of the appliance to work properly.

24.

$0.104 Ω 0.104 Ω$

26.

$2 . 8 × 10 − 2 m 2 . 8 × 10 − 2 m size 12{2 "." "82"´"10" rSup { size 8{-2} } " m"} {}$

28.

$1 . 10 × 10 − 3 A 1 . 10 × 10 − 3 A size 12{1 "." "10"´"10" rSup { size 8{-3} } " A"} {}$

30.

$− 5º C to 45ºC − 5º C to 45ºC$

32.

1.03

34.

0.06%

36.

$− 17º C − 17º C size 12{-"17"°"C"} {}$

38.

(a) $4.7Ω4.7Ω size 12{4 "." 7 %OMEGA } {}$ (total)

(b) 3.0% decrease

40.

$2 . 00 × 10 12 W 2 . 00 × 10 12 W size 12{2 "." "00"´"10" rSup { size 8{"12"} } " W"} {}$

44.

(a) 1.50 W

(b) 7.50 W

46.

$V 2 Ω = V 2 V/A = AV = C s J C = J s = 1 W V 2 Ω = V 2 V/A = AV = C s J C = J s = 1 W$

48.

$1 kW ⋅ h= 1 × 10 3 J 1 s 1 h 3600 s 1 h = 3 . 60 × 10 6 J 1 kW ⋅ h= 1 × 10 3 J 1 s 1 h 3600 s 1 h = 3 . 60 × 10 6 J size 12{1" kW" cdot "h=" left ( { {1 times "10" rSup { size 8{3} } " J"} over {"1 s"} } right ) left (1" h" right ) left ( { {"3600"" s"} over {"1 h"} } right )=3 "." "60" times "10" rSup { size 8{6} } " J"} {}$

50.

$438/y 52.$6.25

54.

1.58 h

56.

\$3.94 billion/year

58.

25.5 W

60.

(a) $2.00×109 J2.00×109 J size 12{2 "." "00"´"10" rSup { size 8{9} } " J"} {}$

(b) 769 kg

62.

45.0 s

64.

(a) 343 A

(b) $2.17×103 A2.17×103 A size 12{2 "." "17"´"10" rSup { size 8{3} } " A"} {}$

(c) $1.10×103 A1.10×103 A size 12{2 "." "17"´"10" rSup { size 8{4} } " A"} {}$

66.

(a) $1.23 × 10 3 kg 1.23 × 10 3 kg$

(b) $2.64 × 10 3 kg 2.64 × 10 3 kg$

69.

(a) $2.08 × 10 5 A 2.08 × 10 5 A$

(b) $4.33 × 10 4 MW 4.33 × 10 4 MW$

(c) The transmission lines dissipate more power than they are supposed to transmit.

(d) A voltage of 480 V is unreasonably low for a transmission voltage. Long-distance transmission lines are kept at much higher voltages (often hundreds of kilovolts) to reduce power losses.

73.

480 V

75.

2.50 ms

77.

(a) 4.00 kA

(b) 16.0 MW

(c) 16.0%

79.

2.40 kW

81.

(a) 4.0

(b) 0.50

(c) 4.0

83.

(a) 1.39 ms

(b) 4.17 ms

(c) 8.33 ms

85.

(a) 230 kW

(b) 960 A

87.

(a) 0.400 mA, no effect

(b) 26.7 mA, muscular contraction for duration of the shock (can't let go)

89.

$1 . 20 × 10 5 Ω 1 . 20 × 10 5 Ω size 12{1 "." "20"´"10" rSup { size 8{5} } %OMEGA } {}$

91.

(a) $1.00Ω1.00Ω size 12{1 "." "00" %OMEGA } {}$

(b) 14.4 kW

93.

Temperature increases $860º C860º C size 12{"860"°C} {}$. It is very likely to be damaging.

95.

80 beats/minute

1.

(a)

3.

10 A

5.

(a)

7.

3.2 Ω, 2.19 A

9.

(b), (d)

11.

9.72 × 10−8 Ω∙m

13.

18 Ω

15.

10:3 or 3.33