The angular position of the reflecting surface of a planar discontinuity with respect to the entry surface is referred to as:

• A. The orientation of the discontinuity
• B. The angle of incidence
• C. The angle of refraction
• D. None of the above

Answer: (A)

The main idea is describing how a flat defect is tilted relative to the surface being scanned. For a planar discontinuity, the angular position of its reflecting surface with respect to the entry surface is called the orientation of the discontinuity. This term specifically names the tilt of the defect plane itself, not the path of the ultrasonic beam. The angle of incidence refers to the beam’s angle relative to the surface normal at the boundary, which is about how the sound hits the surface, not how the defect is oriented. The angle of refraction describes the direction of the beam after it crosses a boundary into another medium, again about the ray, not the defect plane. So orientation is the correct descriptor for the defect’s tilt.