Question

how can ultrasound be used to detect the defect in metal block

Answer 1

well if there are cracks and crevices inside the metal block which is not visible because it is inside... then here is where ultrasound comes in handy... it can detect any defect or cracks inside the metal blocks by the help of Ultrasonic waves... the waves pass through the block and if there's any crack or defect in the block then it gets reflected which is then captured by sensors...

Answer 2

When the ultra sound is release in the block,the rays passes to it if there is any crack the rays deflect back