Question:

A certain element crystallises in a bce lattice of unit cell edge length $27 \backslash \mathrm{AA}$. If the same element under the same conditions crystallises in the fcc lattice, the edge length of the unit cell in $\backslash \mathrm{AA}$ will be________________  (Round off to the Nearest Integer).

[Assume each lattice point has a single atom]

[Assume $\sqrt{3}=1.73, \sqrt{2}=1.41$ ]

Solution:

(33)

For $\mathrm{BCC} \sqrt{3} \mathrm{a}=4 \mathrm{r}$

so $\quad \mathrm{r}=\frac{\sqrt{3}}{4} \times 27$

for $\mathrm{FCC} \quad \mathrm{a}=2 \sqrt{2} \mathrm{r}$

$=2 \times \sqrt{2} \times \frac{\sqrt{3}}{4} \times 27$

$=\frac{\sqrt{3}}{\sqrt{2}} \times 27$

= 33

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