In a B-scan display, the length of a screen indication from a discontinuity is related to which of the following?

• A. The discontinuity's length in the direction of the transducer level
• B. A discontinuity's thickness as measured parallel to the ultrasonic beam
• C. Both A and B
• D. None of the above

Answer: (A)

In a B-scan, the horizontal axis represents the scan position as the transducer moves along the surface, while depth is shown on the vertical axis. So the length of a flaw’s indication on the screen reflects how far the discontinuity extends along the direction you’re scanning. If the defect is long in that direction, the image shows a longer indication; if it’s only thick in the direction parallel to the beam, that dimension doesn’t extend the display horizontally and doesn’t determine screen length. The thickness measured parallel to the ultrasound beam affects other aspects (like amplitude or depth extent) but not the horizontal length of the indication on the B-scan.