College Physics 2e

# Chapter 29

## Problems & Exercises

1.

(a) 0.070 eV

(b) 14

3.

(a) $2.21×1034 J2.21×1034 J$

(b) $2.26×10342.26×1034$

(c) No

4.

263 nm

6.

3.69 eV

8.

0.483 eV

10.

2.25 eV

12.

(a) 264 nm

(b) Ultraviolet

14.

$1.95 × 10 6 m/s 1.95 × 10 6 m/s$

16.

(a) $4.02×1015/s4.02×1015/s$

(b) 0.256 mW

18.

(a) $–1.90 eV–1.90 eV$

(b) Negative kinetic energy

(c) That the electrons would be knocked free.

20.

$6.34 × 10 − 9 eV 6.34 × 10 − 9 eV$, $1.01 × 10 − 27 J 1.01 × 10 − 27 J$

22.

$2 . 42 × 10 20 Hz 2 . 42 × 10 20 Hz$

24.
$hc = 6.62607 × 10 − 34 J ⋅ s 2.99792 × 10 8 m/s 10 9 nm 1 m 1.00000 eV 1.60218 × 10 − 19 J = 1239.84 eV ⋅ nm ≈ 1240 eV ⋅ nm hc = 6.62607 × 10 − 34 J ⋅ s 2.99792 × 10 8 m/s 10 9 nm 1 m 1.00000 eV 1.60218 × 10 − 19 J = 1239.84 eV ⋅ nm ≈ 1240 eV ⋅ nm$
26.

(a) 0.0829 eV

(b) 121

(c) 1.24 MeV

(d) $1.24×1051.24×105$

28.

(a) $25.0 × 103 eV 25.0 × 103 eV$

(b) $6.04 × 1018 Hz 6.04 × 1018 Hz$

30.

(a) 2.69

(b) 0.371

32.

(a) $1.25 × 1013 photons/s 1.25 × 1013 photons/s$

(b) 997 km

34.

$8.33 × 10 13 photons/s 8.33 × 10 13 photons/s$

36.

181 km

38.

(a) $1.66 × 10 − 32 kg ⋅ m/s 1.66 × 10 − 32 kg ⋅ m/s$

(b) The wavelength of microwave photons is large, so the momentum they carry is very small.

40.

(a) 13.3 μm

(b) $9.38×10-29.38×10-2$ eV

42.

(a) $2.65×10−28kg⋅m/s2.65×10−28kg⋅m/s$

(b) 291 m/s

(c) electron $3.86×10−26 J3.86×10−26 J$, photon $7.96×10−20 J7.96×10−20 J$, ratio $2.06×1062.06×106$

44.

(a) $1.32×10−13 m1.32×10−13 m$

(b) 9.39 MeV

(c) $4.70×10−2 MeV4.70×10−2 MeV$

46.

$E=γmc2mc2E=γmc2mc2$ and $P=γmuP=γmu$, so

$EP = γmc2 γmu = c2 u . EP = γmc2 γmu = c2 u .$

As the mass of particle approaches zero, its velocity $uu$ will approach $cc$, so that the ratio of energy to momentum in this limit is

$limm→0 E P = c2 c = c limm→0 E P = c2 c = c$

which is consistent with the equation for photon energy.

48.

(a) $3 . 00 × 10 6 W 3 . 00 × 10 6 W$

(b) Headlights are way too bright.

(c) Force is too large.

49.

$7.28 × 10 –4 m 7.28 × 10 –4 m$

51.

$6.62 × 10 7 m/s 6.62 × 10 7 m/s$

53.

$1.32 × 10 –13 m 1.32 × 10 –13 m$

55.

(a) $6.62×107 m/s6.62×107 m/s$

(b) $22.9 MeV22.9 MeV$

57.
15.1 keV
59.

(a) 5.29 fm

(b) $4.70×10−12 J4.70×10−12 J$

(c) 29.4 MV

61.

(a) $7.28×1012 m/s7.28×1012 m/s$

(b) This is thousands of times the speed of light (an impossibility).

(c) The assumption that the electron is non-relativistic is unreasonable at this wavelength.

62.

(a) 57.9 m/s

(b) $9.55×10−9 eV9.55×10−9 eV$

(c) From Table 29.1, we see that typical molecular binding energies range from about 1eV to 10 eV, therefore the result in part (b) is approximately 9 orders of magnitude smaller than typical molecular binding energies.

64.

29 nm,

290 times greater

66.

$1 . 10 × 10 − 13 eV 1 . 10 × 10 − 13 eV$

68.

$3 . 3 × 10 − 22 s 3 . 3 × 10 − 22 s$

70.

$2.66 × 10 − 46 kg 2.66 × 10 − 46 kg$

72.

0.395 nm

74.

(a) $1.3 × 10 − 19 J 1.3 × 10 − 19 J$

(b) $2 . 1 × 10 23 2 . 1 × 10 23$

(c) $1 . 4 × 10 2 s 1 . 4 × 10 2 s$

76.

(a) $3.35×105 J3.35×105 J$

(b) $1.12×10–3 kg⋅m/s1.12×10–3 kg⋅m/s$

(c) $1.12×10–3 m/s1.12×10–3 m/s$

(d) $6.23×10–7 J6.23×10–7 J$

78.

(a) $1.06×1031.06×103$

(b) $5.33×10−16kg⋅m/s5.33×10−16kg⋅m/s$

(c) $1.24×10−18m1.24×10−18m$

80.

(a) $1 . 62 × 10 3 m/s 1 . 62 × 10 3 m/s$

(b) $4 . 42 × 10 − 19 J 4 . 42 × 10 − 19 J$ for photon, $1 . 19 × 10 − 24 J 1 . 19 × 10 − 24 J$ for electron, photon energy is $3 . 71 × 10 5 3 . 71 × 10 5$ times greater

(c) The light is easier to make because 450-nm light is blue light and therefore easy to make. Creating electrons with $7.43 μeV 7.43 μeV$ of energy would not be difficult, but would require a vacuum.

81.

(a) $2 . 30 × 10 − 6 m 2 . 30 × 10 − 6 m$

(b) $3 . 20 × 10 − 12 m 3 . 20 × 10 − 12 m$

83.

$3 . 69 × 10 − 4 ºC 3 . 69 × 10 − 4 ºC$

85.

(a) 2.00 kJ

(b) $1.33×10−5kg⋅m/s1.33×10−5kg⋅m/s$

(c) $1.33×10−5 N1.33×10−5 N$

(d) yes

87.

(a)

(b)

(c) Yes, conservation of momentum applies.

(d) The photon with the longer wavelength has less momentum than the one with the shorter wavelength.

Order a print copy

As an Amazon Associate we earn from qualifying purchases.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.