# Materials Science Questions and Answers – Linear Defects – 2

This set of Materials Science Question Paper focuses on “Linear Defects – 2”.

1. Which type of defect are line defects?
a) One-dimensional defect
b) Zero-dimensional defect
c) Two-dimensional defect
d) Three-dimensional defect

Explanation: Line defects are one dimensional defects as they extend in a singular direction in space. Line defects are present in solids whereas the whole row of atoms is arranged in anomalous order. Hence line defects are linear defects and one dimensional in nature.

2. 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.

3. Which of the following statement is false?
a) Burger vector is the right angle to edge dislocation
b) In screw defect the line defect is parallel to the displacement vector
c) Grain boundary defect is a type of line defect
d) Line defect occurs during the recrystallization process or during slip

Explanation: Grain boundary defect is a two-dimensional defect. Grain boundary is the interface between two grains and hence they stop the dislocations from moving freely. Therefore, they cause a two-dimensional defect to spread around the grain boundary.

4. 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.

5. 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.
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6. To determine yield strength of a material which of the following needn’t be affected?
a) Solute hardening
b) Precipitation hardening
c) Work hardening
d) Martensic transformation

Explanation: Burgers vector plays an important role in determining yield strength by affecting solute hardening, precipitation hardening and work hardening. Martensic transformation which refers to quenching from high temperature doesn’t play any role in the determination of yield strength.

7. 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 named screw dislocation.

8. In an 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 an atom is inserted and a screw like path is not traced by the dislocation.

9. Which of the following is fields are not present for edge dislocation?
a) Tensile
b) Compressive
c) Shear stress
d) Strain

Explanation: In the edge dislocation, tensile, compressive and shear stress field are present due to an additional half plane of atom added because of which stresses are produced but no strain is produced because of an edge dislocation.

10. 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.

11. 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.

12. What are 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 dislocation 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.

13. Which of the following can be theoretical shear stress produced in metals? ( GPa stands for Giga pascal)
a) 10 GPa
b) 32 GPa
c) 2 GPa
d) 50 GPa

Explanation: The theoretical shear stress is in the range of 3 Gpa to 30 GPa. 10GPa is the only option which lies within that range while 32 GPa, 2 GPa and 50 GPa are beyond the range in which the theoretical shear stress can lie for pure metal.

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