The document discusses different types of crystal structures and defects in engineering materials. It provides multiple choice questions to test understanding of concepts like screw dislocations, Burger's vector, point defects including vacancies and interstitials, and imperfection types such as Schottky and Frenkel defects. Correct answers are given regarding the orientation and motion of screw dislocations as well as the dimensions and nature of different defect types.

1. ENGINEERING MATERIALS
CRYSTAL STRUCTURES

16. 1. A screw dislocation.
1. lies parallel to its Burger's vector.
2. lies perpendicular to its Burger's vector
3. Moves in perpendicular direction to the Burger's
vector.
4. Moves in an inclined direction to the Burger's
vector.
Select the correct answer using the codes given
below:
(a) 1 and 4 (b) 1 and 3
(c) 2 and 3 (d) 2 and 4

17. 2. A cation vacancy and an anion vacancy in a crystal of
the type AB is called
(a) Schottky defect
(b) Frenkel defect
(c) Pair of vacancies
(d) None of the above

18. 3. Which of the following is NOT a point defect?
(a) Edge dislocation
(b) Vacancy
(c) Substitutional impurity
(d) Interstitial impurity

19. 4. Which of the following are zero dimensional defects?
1. Vacancy
2. Interstitial defect
3. Substitutional defect
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3

20. 5. Schottky imperfection is a
(a) Point imperfection
(b) Line imperfection
(c) Surface imperfection
(d) Volume imperfection

21. 6. The Burger’s vector lies parallel to the dislocation line
along the axis of a line of atoms in the same plane is:
(a) Screw dislocation
(b) Edge dislocation
(c) Cracks
(d) Vacancies