Materials Science Multiple Choice Questions & Answers (MCQs) on “Concept of Dislocations”.
1. Edge dislocation and skew dislocation are linear crystalline defects.
a) True
b) False
Answer: a
Clarification: Line defects are mainly dislocations which can be broadly classified into two distinct defects. These two dislocations are called edge dislocation and screw dislocation.
2. In which type of dislocation an extra plane is inserted inside the crystal?
a) Edge dislocation
b) Screw dislocation
c) Jog dislocation
d) Mixed dislocation
Answer: a
Clarification: The edge defect is simply pictured as an additional half plane of atoms in a lattice. The dislocations are termed a line defect because of the number of defective points created within the lattice along a line. Hence, an extra plane of atoms is added inside the crystal in this type of defect.
3. What is the difference between the angle of Burgers vector and dislocation line in edge dislocation and screw dislocation?
a) -90 degrees
b) 0 degrees
c) 45 degrees
d) 90 degrees
Answer: d
Clarification: The angle between Burgers vector and dislocation line in edge dislocation is 90 degrees while the angle between burger vector and dislocation line for screw dislocation is 0 degree. To find the difference we have subtract 0 from 90, giving us 90 degrees as our final answer.
4. In which type of dislocation planes are displaced relative to each other through shear?
a) Edge dislocation
b) Screw dislocation
c) Jog dislocation
d) Mixed dislocation
Answer: b
Clarification: In screw dislocation, planes are displaced relative to each other through shear. The trace of the atomic planes around the screw dislocation makes spiral or whorled path sort of resembling a screw and hence, it is name screw dislocation.
5. In edge dislocation, a helical path is traced around the dislocation line.
a) True
b) False
Answer: b
Clarification: A helical path is traced along the dislocation line in screw dislocation whereas in edge dislocation a new additional half plane of atom is inserted and a screw like path is not traced by the dislocation.
6. Which of the following is fields are not present for edge dislocation?
a) Tensile
b) Compressive
c) Shear stress
d) Strain
Answer: d
Clarification: In an edge dislocation, tensile, compressive and shear stress field are present due to additional half plane of atom added because of which stresses are produced but no strain is produced because of the edge dislocation.
7. Which of the following is fields are present for screw dislocation?
a) Tensile
b) Compressive
c) Shear stress
d) Strain
Answer: c
Clarification: As in screw dislocation a helical path is traced along a dislocation line, there is only presence of shear stress field and no compressive, tensile or strain field is produced. Shear stress field is produced due to the spiral aspect of this type of dislocation.
8. Which of the following dislocation can glide but not climb?
a) Screw dislocation
b) Edge dislocation
c) Jog dislocation
d) Mixed dislocation
Answer: a
Clarification: Screw dislocation can only glide in a crystal lattice along the helical path while edge dislocations can glide and climb as there is an extra plane of atom present.
9. What is the dislocation in which the line direction and Burgers vector are neither perpendicular nor parallel?
a) Screw dislocation
b) Edge dislocation
c) Jog dislocation
d) Mixed dislocation
Answer: d
Clarification: Mixed dislocations are dislocation consisting of both screw and edge dislocation character where in screw dislocation the line direction and burger vector are parallel and for edge dislocation it is perpendicular. Therefore, the angle between line direction and Burgers vector is neither perpendicular nor parallel.
10. What can be the unit of dislocation density?
a) mm-2
b) mm-3
c) mm2
d) mm
Answer: a
Clarification: Dislocation density is defined as the total dislocation length per unit volume and unit of length is mm and that of volume is mm3 therefore, the unit of dislocation density will be mm-2.