16 Marks Questions, Assignment Problems

ANNA UNIVERSITY PART-B (16 Marks) Questions

1. Define the terms atomic radius and packing factor. Calculate the above for BCC and FCC structures.

2. Calculate the number of atoms per unit cell, coordination number and packing factor for FCC and BCC structures. 

3. Describe the structure of a HCP crystal. Give details about its atomic radius, atomic packing factor and axial ratio. 

4. What is packing factor? Prove that the packing factor of HCP is 0.74.

5. Describe the arrangement of atoms in FCC and HCP structures and show that both these structures have the same atomic packing factor.

ADDITIONAL PART B (16 Marks) Questions

1. Explain crystal defects in a detailed manner.

ASSIGNMENT PROBLEMS

1. Calculate the lattice constant of Molybdenum with BCC structure and density of 10.2 × 103 kg/m3. The atomic weight of Molybdenum is 95.94. (Given Avagadro number is 6.02 × 1026)

(Ans: 3.149 Å)

2. The lattice constant of a metal with cubic lattice is equal to 2.88 Å. The density of the metal is 7.20 gm/cm3. Calculate the number of unit cell present in 1 kg of metal.

(Ans: 5.8 × 1024)

3. Copper crystallises in the FCC structure. The density and atomic weight of copper are 8960 kg/m3 and 63.54 respectively. Calculate its lattice constant.

(Ans: 3.6 Å )

4. The atomic packing efficiency of a crystal is 68% and the closest distance of approach between its neighbouring atom is 2.62 Å. Calculate density of the crystal if the mass of its one atom is 50.04 amu.

(Ans: 6000 kg/m2)

5. Ni has FCC structure with lattice constant 3.52 Å. Calculate the interplanar spacings for (a) (101) plane (b) (123) plane (c) (320) plane.

(Ans: 2.49 × 10-16 m, 9.41 × 10-11 m and 9.76 × 10−11 m)