question_answer

       Explain how defects in a metal block can be detected using ultrasound.

Answer:

                  The flaws like internal cracks, etc., in the metal blocks are detected by using ultrasound. This is based on the fact that the internal crack (or hole) in the block does not allow ultrasonic wave to pass through it. To detect the flaw in metallic block, a source of ultrasonic is placed in front of one face of 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. (a) If the ultrasonic waves passes uninterrupted through all parts of metal block, then there is no defect in block. (b) If the ultrasonic waves do not reach the opposite face, then the block has defect (like a crack or a hole).