Question

explain how defects in a metal block can be detected by ultrasound

Answer 1

Ultrasounds can be used to detectcracks and flaws in metal blocks.Ultrasonic waves are allowed to pass through the metallic block and detectors are used to detect the transmitted waves. If there is even a small defect, theultrasound gets reflected back indicating the presence of the flaw or defect.
These are used in automobile industries,aviation industries.shipbuilding etc.

Hope this helps.

Answer 2

Ultrasonic sound is used for detecting defects in metal block because when Ultrasonic waves are sent through the metal block. There are detectors at the other end. They catch the wave. Even if there is a small crack or flaw in the block the waves return back or divert and it doesn't reach to the detector. Thus, defects are detected.