21. In a B-Z constructed from a given fcc lattice with a = b = c and a ¼ b ¼ c ¼
90
: the eight hexagonal equivalent zone faces from the center of the zone are at
a distance:
(a) p=a
ð Þ
(b)
ffiffi ffi
2
p p=a
ð Þ
(c)
ffiffi ffi
3
p p=a
ð Þ
(d) 2 p=a
ð Þ
22. In a B-Z constructed from a given fcc lattice with a = b = c and a ¼ b ¼ c ¼
90
: the six square equivalent zone faces from the center of the zone are at a
distance:
(a) p=a
ð Þ
(b)
ffiffi ffi
2
p p=a
ð Þ
(c)
ffiffi ffi
3
p p=a
ð Þ
(d) 2 p=a
ð Þ
23. In a B-Z constructed from a given simple hexagonal lattice with a = b 6 ¼ c and
a ¼ b ¼ 90
and c ¼ 120
; the six vertical planes from the center of the zone
are at a distance:
(a)
p
a
À Á
(b)
2p
a
À Á
(c)
1 ffiffi
3
p p
a
À Á
(d)
2 ffiffi
3
p p
a
À Á
24. In a square lattice, the distance of a corner of the first BZ from the center is:
(a) p=a
ð Þ
(b)
ffiffi ffi
2
p p=a
ð Þ
(c)
ffiffi ffi
3
p p=a
ð Þ
(d) 2 p=a
ð Þ
25. The radius of the Fermi circle for a monovalent metal is:
(a) 0:798
p
a
À Á
(b) 1:228
p
a
À Á
(c) 1:382
p
a
À Á
(d) 1:596
p
a
À Á
26. The radius of the Fermi circle for a divalent metal is:
(a) 0:798
p
a
À Á
(b) 1:228
p
a
À Á
(c) 1:382
p
a
À Á
(d) 1:596
p
a
À Á
2.4 Fermi Surface and Brillouin Zone
91