(c) 1039.84Å
3
(d) 1139.84Å
3
20. A primitive tetragonal unit cell has a = 5 Å, b = 6 Å, and c = 7 Å; a = b =
= 90°. A new unit cell is chosen with edges defined by the vectors from the
origin to the points with coordinates: 3, 1, 0; 1, 2, 0 and 0, 0, 1. The number of
lattice points in the new unit cell is:
(a) 8
(b) 7
(c) 6
(d) 5
21. The linear atomic density (i.e., the number of atoms/m) along [11] of the
centered rectangular lattice with a = 3 Å and b = 4 Å is:
(a) 4 Â 10
9
(b) 5 Â 10
9
(c) 6 Â 10
9
(d) 7 Â 10
9
22. The linear atomic density (i.e., the number of atoms/m) along [110] in fcc
copper whose lattice parameter a = 3.61 Å is:
(a) 5.92 Â 10
9
(b) 4.92 Â 10
9
(c) 3.92 Â 10
9
(d) 2.92 Â 10
9
23. The linear atomic density (i.e., the number of atoms/m) along [111] in fcc
copper whose lattice parameter a = 3.61 Å is:
(a) 4.60 Â 10
9
(b) 3.60 Â 10
9
(c) 2.60 Â 10
9
(d) 1.60 Â 10
9
24. The linear atomic density (i.e., the number of atoms/m) along [110] in bcc iron
whose lattice parameter a = 2.87 Å:
(a) 1.46 Â 10
9
(b) 2.46 Â 10
9
(c) 3.46 Â 10
9
(d) 4.46 Â 10
9
3.6 Packing Efficiency
131