Engineering Questions with Answers - Multiple Choice Questions

# Materials Science MCQ’s – Concept of Dislocations

1 - Question

Edge dislocation and skew dislocation are linear crystalline defects.
a) True
b) False
Explanation: 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 - Question

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
Explanation: 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 - Question

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
Explanation: 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 - Question

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
Explanation: 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 - Question

In edge dislocation, a helical path is traced around the dislocation line.
a) True
b) False
Explanation: 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 - Question

Which of the following is fields are not present for edge dislocation?
a) Tensile
b) Compressive
c) Shear stress
d) Strain
Explanation: 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 - Question

Which of the following is fields are present for screw dislocation?
a) Tensile
b) Compressive
c) Shear stress
d) Strain
Explanation: 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 - Question

Which of the following dislocation can glide but not climb?
a) Screw dislocation
b) Edge dislocation
c) Jog dislocation
d) Mixed dislocation
Explanation: 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 - Question

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
Explanation: 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 - Question

What can be the unit of dislocation density?
a) mm-2
b) mm-3
c) mm2
d) mm