bei48482_FM

Answers to Odd-Numbered Exercises 521

9. 1.05 105 K.


10. 15.4 pm.


11. (1)av(1N) 



0 (1)n() d.

15. A fermion gas will exert the greatest pressure because the Fermi distribution has
    a larger proportion of high-energy particles than the other distributions; a boson
    gas will exert the least pressure because the Bose distribution has a larger pro-
    portion of low-energy particles than the others.


16. 2.5 106 ; 2.5 102.


17. 1.3 percent.


18. 0.92 kW/m^2.


19. 527°C.


20. 51 W.


21. 494 cm^2 ; 6.27 cm.


22. 2.5 percent.


23. 1.0 104 K.


24. 2.9 102 K; 8.9 1011 m.


25. 3.03 10 ^12 J/K.


26. (a) 3.31 eV. (b) 2.56 104 K. (c) 1.08 106 m/s.


27. 11 eV.


28. 1.43 1021 states/eV; yes.


29. At 20°C, A(Nh^3 V)(2mHekT)^3 ^2 3.56 10 ^6 , so A1.


30. At 20°C, A(Nh^3  2 V)(2mekT)^3 ^2 3.50 10 ^3 , so A1.


31. (a) 1.78 eV; 128 keV. (b) kT862 eV, so the gas of nuclei is nondegenerate
    but the electron gas is degenerate.

CHAPTER 10

1. The greater the atomic number Zof a halogen ion, the larger it is, hence the
   increase in interionic spacing with Z. The larger the ion spacing, the smaller the
   cohesive energy, hence the lower the melting point.


2. (a) 7.29 eV. (b) 9.26.


3. The heat lost by the expanding gas is equal to the work done against the attrac-
   tive van der Waals forces between its molecules.


4. (a) Van der Waals forces increase the cohesive energy since they are attractive.
   (b) Zero-point oscillations decrease the cohesive energy since they represent a
   mode of energy possession present in a solid but not in individual atoms or ions.


5. Only the outer shell electrons in the atoms of a metal are members of its “gas”
   of free electrons.


6. 1.64 10 ^8 m.


7. In both, a forbidden band separates a filled valence band from the conduction
   band above it. In semiconductors the band gap is smaller than in insulators, small
   enough so that some valence electrons have enough thermal energy to jump
   across the gap to the conduction band.


8. (a) Photons of visible light have energies of 13 eV, which can be absorbed by
   free electrons in a metal without leaving its valence band. Hence metals are
   opaque. The forbidden bands in insulators and semiconductors are too wide for
   valence electrons to jump across them by absorbing only 13 eV. Hence such
   solids are transparent. (b) Silicon,1130 nm; diamond,207 nm.


9. (a) p-type. (b) Aluminum atoms have 3 electrons in their outer shells, germa-
   nium atoms have 4. Replacing a germanium atom with an aluminum atom leaves
   a hole, so the result is a p-type semiconductor.

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