1.The atomic packing fraction in a simple cubic unit cell is ________
a) 0.74
b) 0.52
c) 0.68
d) 0.66
Explanation: a=r and APF = (volume of effective number of atoms/volume of unit cell).
2. The atomic packing fraction in a body centered cubic unit is cell is __________
a) 0.74
b) 0.52
c) 0.68
d) 0.66
Explanation: r=(√3)/4×a and APF = (volume of effective number of atoms/volume of unit cell)
3. If the radius of a copper atom is given as 1.27 Ao, its density (in kg/m3) will be?
a) 100.01
b) 86.25
c) 8979
d) 7968
Explanation: Formula to calculate the density of a cubic metal:
ρ (kg/m3) = \(\frac{n × A.W}{a^3}\) × 1.66 × 10-27
[where, ρ = density of metal, n = effective number of atoms per unit cell, A.W = Atomic weight of the metal in amu and a = lattice parameter in meter] Given: radius of copper = 1.27 Ao = 1.27×10-10 m
We know that atomic weight of copper = 63.5 amu
Lattice parameter to atomic radius relation for cubic structures are as follows:
| Crystal Structure | Effective Number of Atoms per Unit Cell | Effective Number of Atoms per Unit Cell |
|---|---|---|
| Simple Cubic (SC) | a = 2r | 1 |
| Body Centered Cubic (BCC) | a = 4r/√3 | 2 |
| Face Centered Cubic (FCC) | a = 4r/√2 | 4 |
| Hexagonal Close Packed Cubic (HCP) | a = 2r | 6 |
Therefore, lattice parameter of copper (a) = (4×1.27×10-10)/√2 = 3.59×10-10 m
Therefore, density of copper = \(\frac{4 × 63.5}{(3.59 × 10^{-10})^3}\) × 1.66 × 10-27 ≈ 8979 kg/m3.
4. The atomic packing fraction in a face centered cubic unit is?
a) 0.74
b) 0.52
c) 0.68
d) 0.66
Explanation: a=2√2×r and APF = (volume of effective number of atoms/volume of unit cell).
5. Vacancy defects in solids is a sub type of ___________
a) Point imperfections
b) Line imperfections
c) Volume imperfections
d) Surface imperfections
Explanation: The simplest of the point defects is a vacancy, vacant lattice site. This could occur an atom is being missing from its lattice site. All crystalline solids contains vacancies, in fact, it is impossible for a material to be free of these vacancies, making them to call equilibrium defects.
6. Substitution of a foreign atom in the site of parent atom in the crystal is a?
a) Vacancy defect
b) Substitution impurity
c) Volume imperfection
d) defect
Explanation: When an impurity atom of equal to atomic size of the host atom is being replaced or substituted for the host atoms, is called substitutional impurity.
7. Edge dislocation imperfection is a sub type of ______________
a) Point imperfections
b) Line imperfections
c) Volume imperfection
d) Surface imperfections
Explanation: A dislocation is a one-dimensional or linear defect around which some of the atoms are misaligned. Edge dislocation is a type of dislocation, where an extra portion of plane of atoms, the edge terminates within the crystal.
8. Displacement of an ion from regular location to interstitial location is known as ____________
a) Vacancy defect
b) Line imperfection
c) Schottky’s defect
d) Frenkel defect
Explanation: Frenkel defect, named after its discoverer “Yakov Frenkel”, forms when an atom leaves its regular position thus creating a vacancy there, and becomes interstitial by positioning itself into nearby interstitial location. Usually small ion (cation) undergoes this phenomenon.
9. When a pair of cation and anion are missing in a crystal, it is called ____________
a) Vacancy defect
b) Line imperfection
c) Schottky’s defect
d) Frenkel defect
Explanation: Schottky’s defect, named after its discoverer “Walter H. Schottky”, forms when two atoms of opposite charge (anion and cation) leaves their regular atomic positions thus creating two vacancies. As two atoms of opposite charges are leaving, there is no change in overall charge of the material with Schottky’s defect. Schottky’s defect is known for its presence in ionic crystals.
10. Which one of the following is not a zero-dimensional defect?
a) Vacancy defect
b) Substitution imperfection
c) Schottky’s defect
d) Screw dislocation
Explanation: Screw dislocation is a type of dislocations (linear or one-dimensional defects) which thought to be formed by a shear stress that is applied to produce the distortion in a spiral manner inside the crystal, indicating burgers vector parallel to this dislocation type.