ANS:A - more

The elastic strain energy of a unit length of an edge dislocation is more than that of a screw dislocation. Explanation:

1. Types of Dislocations: Dislocations are line defects in the crystal lattice of materials. Two common types of dislocations are edge dislocations and screw dislocations.
2. Edge Dislocation: In an edge dislocation, the extra half-plane of atoms is inserted into the crystal lattice along the dislocation line. This creates regions of compressive and tensile strains around the dislocation line.
3. Screw Dislocation: In a screw dislocation, the atoms are displaced parallel to the dislocation line, resulting in a spiral or helical motion of atomic planes around the dislocation line. The strain field around a screw dislocation is rotational.
4. Elastic Strain Energy: Elastic strain energy is the energy stored in a material due to deformation under an applied load. It is proportional to the square of the strain and depends on the nature of the dislocation.
5. Comparison: The elastic strain energy of an edge dislocation is more than that of a screw dislocation. This is because the strain field around an edge dislocation is more concentrated and extends farther from the dislocation line compared to a screw dislocation. As a result, the energy associated with the distortion of atomic bonds and the strain field is higher for an edge dislocation.
6. Physical Interpretation: Edge dislocations have a higher energy per unit length because they create significant distortions in the lattice structure, leading to larger elastic strain energy compared to screw dislocations.