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QUESTION: 1

Which of the following has bcc structure?

Solution:

The correct answer is: CsCI

QUESTION: 2

If is wave vector of incident X-ray and be the reciprocal lattice vector then condition for Bragg reflection is given by :

Solution:

**Correct Answer :- b**

**Explanation : **Bragg reflection or diffraction occurs when light waves are incident on an ultrasonic wave with a comparable wavelength. The light is reflected in a specular fashion by the ultrasonic grating, and undergoes constructive interference in accordance with Bragg's law.

Let be the scattered wave vector, then from Ewald construction :

K' = K - G....(i)

Since, for elastic scattering, there will be no change in the magnitude of the vector i.e.

|K| = K' = 2pi/λ

Now squaring (i),

K^{2} = K^{2} + G^{2} - 2K . G

G^{2} = 2K . G

QUESTION: 3

Which of the following lattices has the least packing fraction?

Solution:

packing fraction of simple cubic = 52% packing fraction of bee = 68%

packing fraction of fee = 74%

packing fraction of diamond = 34%

The correct answer is: diamond

QUESTION: 4

The radii of Cs and Cl are r_{1} and r_{2} respectively. Which of the following gives the lattice constant of CsCI if it is crystalized in bcc structure :

Solution:

For bcc structure ,

The correct answer is:

QUESTION: 5

A lattice is characterized by following primitive vectors

Solution:

Hence, lattice is bcc with edge π

The correct answer is: bcc with cube edge π

QUESTION: 6

What is the reciprocal lattice to simple cubic lattice?

Solution:

Primitive translation Vectors of simple cubic lattice may be written as :

Then primitive translation vector of reciprocal lattice is

Hence, the reciprocal lattice is itself a simple cubic lattice with lattice constant

The correct answer is: simple cubic

QUESTION: 7

A body centred cubic lattice has edge a. Edge of its primitive cells will be :

Solution:

from figure, AB = a

The correct answer is:

QUESTION: 8

The primitive translation vectors of the fcc lattice are

The volume of the primitive cell of reciprocal lattice is :

Solution:

**The correct option is D**

The primitive translation vector of the reciprocal lattice to the above lattice be calculated as :

b_{1}=(2π/a)(-i+j+k);

b_{2}=(2π/a)(i-j+k);

b_{3}=(2π/a)(i+j-k);

volume of the reciprocal lattice is:

=(2π/a)^{3}[(-i+j+k) (i-j+k)]

=4(2π/a)^{3}

The correct answer is, 4(2π/a)^{3}

QUESTION: 9

The positions of number of nearest neighbours in a unit cell of bcc structure is given by:

Solution:

Nearest neighbour to an atom (say at origin) is the atom present is the centre of the

at point P and the position of P can be =

The correct answer is: =

QUESTION: 10

What is the second nearest neighbour distance in a face centered cubic whose conventional unit cell parameter is a?

Solution:

Here AC is the nearest distance while AB or AD forms the nearest neighbour distance which is equal to ' a '.

The correct answer is: a

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