# Mechanical Behaviour Questions and Answers – Burgers Vector

This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Burgers Vector”.

1. A Burgers vector represents the extent of _____
a) Slip
b) Elastic deformation
c) Twinning
d) Hardness

Explanation: A Burgers vector represents the extent of slip. The extent of slip may also be referred as an extent of plastic deformation. Burgers vector represents a magnitude of slip.

2. For BCC Burgers vector is ____ and for FCC ____
a) a <hkl>, a <hkl>
b) a <hkl>, (a/2) <hkl>
c) (a/2) <hkl>, a <hkl>
d) (a/2) <hkl>, (a/2) <hkl>

Explanation: For BCC burgers vector is represented as (a/2) <hkl>. For FCC burgers vector is (a/2) <hkl>. While for simple cubic it is a <hkl>.

3. Burgers vector is a measure of the lattice distortion due to the presence of ____
a) Point defect
b) Line defect
c) Surface defect
d) Volume defect

Explanation: Burgers vector measures the lattice distortion. It can measure this distortion generated from line defect. This includes a dislocation defect.

4. In perfect dislocations Burgers vector is ____ and in partial dislocation is ______
a) Translation vector, translation vector
b) Translation vector, not a translation vector
c) Not a translation vector, translation vector
d) Not a translation vector, not a translation vector

Explanation: In a perfect dislocation Burgers vector is translation vector. In a partial dislocation Burgers vector is not a translation vector. Translation vector is defined as the distance to which an atom must be shifted to move it in other unit cells.

5. Elastic energy of a dislocation is _______
a) ∝ b
b) ∝ b2
c) ∝ b3
d) ∝ √b

Explanation: Elastic energy of dislocation is proportional to the square of Burgers vector. It is given by Eelastic = lGb2. Here l is length, G is shear modulus and E is an elastic energy of dislocation.
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6. Relation E ∝ b2 is known as ______
a) Frank’s rule
b) Burgers law
c) Bauschinger effect
d) Griffith law

Explanation: Eelastic = lGb2, here l is length, G is shear modulus and E is elastic energy of dislocation. It gives E ∝ b2. This is known as Frank’s rule.

7. A dislocation loop can form by clustering of ______
a) Impurity atoms
b) Vacancies
c) Interstitials
d) Gas atoms

Explanation: Dislocation loop can form by clustering of vacancies. This cluster is in the form of a disc. It forms on the close packed plane.

8. What is the angle between the Burgers vector and the plane of the dislocation loop?
a) 0°
b) <90°
c) 90°
d) >90°

Explanation: Dislocation loop forms by a collection of vacancies on close packed plane. Burgers vector is perpendicular to the loop. That’s why it shows edge character.

9. For a dislocation, Burgers vector _____ with varying position.
a) Changes slowly
b) Changes abruptly
c) Changes with a constant rate
d) Doesn’t change

Explanation: For any dislocation Burgers vector remains invariant. It means it does not vary with varying position.

10. Dislocation in loop form has the same Burgers vector and character at all positions.
a) True
b) False

Explanation: Dislocation in crystals can exist in form of curve or loop. In loop form it has the same Burgers vector at all positions. But its character changes along the loop.

11. A prismatic loop has ____ character over the entire length.
a) Edge
b) Screw
c) Mixed
d) Edge and screw

Explanation: The dislocation loop made from a collection of vacancies is called Prismatic loop. In it, Burgers vector is perpendicular to the plane of the loop. That’s why it shows edge character over the entire length.

12. The plane containing burgers vector and tangent vector allows glide of dislocation.
a) True
b) False

Explanation: The plane, which contains a Burgers vector and tangent vector both, allows dislocation motion. This motion is known as glide. This plane is commonly close packed plane.

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