Question

Which statements are correct for edge dislocation?
A. An edge dislocation moves in the direction of the Burger vector.
B. An edge dislocation involves an extra row of atoms above the slip plane.
C. An edge of the atomic plane is formed internal of the crystal.
D. The Burger vector of an edge dislocation is parallel to the dislocation line.
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A, B and C only
• C. A, B, C and D
• D. B, C and D only

Hint:

Remember the key difference between edge and screw dislocations regarding the Burgers vector (\(\vec{b}\)) and the dislocation line (\(\vec{t}\)):

\textbf{Edge Dislocation:} \( \vec{b} \perp \vec{t} \)
\textbf{Screw Dislocation:} \( \vec{b} \parallel \vec{t} \)
This distinction is a very common topic in exam questions.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
An edge dislocation is a linear crystal defect where an extra half-plane of atoms is introduced into the lattice. The dislocation line is the edge of this half-plane. The Burgers vector describes the magnitude and direction of the lattice distortion.
Step 2: Detailed Explanation:
Statement A: The slip caused by the movement of an edge dislocation is in the direction of the Burgers vector. The dislocation line itself moves on the slip plane in response to a shear stress, and its direction of motion is parallel to the Burgers vector. Therefore, this statement is correct.
Statement B: The definition of an edge dislocation is the insertion of an extra half-plane (or row) of atoms. This statement correctly describes the physical nature of an edge dislocation. So, statement B is correct.
Statement C: The extra half-plane of atoms terminates within the crystal. The line along which it terminates is the dislocation line, which is internal to the crystal. So, statement C is correct.
Statement D: For an edge dislocation, the Burgers vector (\(\vec{b}\)) is perpendicular (\(\perp\)) to the dislocation line (\(\vec{t}\)). The Burgers vector is parallel to the dislocation line only for a screw dislocation. So, statement D is incorrect.
Step 3: Final Answer:
The correct statements are A, B, and C.