UPSEE Solved Model Paper 1

ρ =

n×Mm NA×a2

NA×a2

For fcc centred cubic cell 𝑛 = 4, 𝑎 = 3.5Å
∴ ρ(fcc) =

4×Mm

NA×(3.5)3

... (i)
or bcc lattice
𝑛 = 2, 𝑎 = 3.0Å
∴ ρ(bcc) =

2×Mm

NA×(3.0)2

... (ii)
From equation (i) and (ii), we get
∴

ρ(fcc)

ρ(bcc)

=

4

2

=

33

(3.5)3

=

4×3×3×3

2×3.5×3.5×3.5

= 1.259