Question

Ordinary sound wave can detect cracks in metals salck. Why?

Answer 1

Ultrasounds can be used to detect cracks and flaws in metal blocks. Metallic components are used in the construction of big structures like buildings, bridges, machines and scientific equipments. The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure. 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, the ultrasound gets reflected back indicating the presence of the flaw or defect.

Answer 2

Ultrasounds are waves having frequency greater than 20 kHz. The flaws like internal cracks, etc. the metal blocks are detected by using ultrasound. It is based on the fact that internal crack or hole in the block does not allow ultrasonic waves to pass through it. To detect flaw in metallic blocks, a source of ultrasonic sound is placed in front of one face of the block and a detector on the opposite face. The ultrasonic waves are produced and made to pass through one face of block and detected on the opposite face.