I have the last Physics Exam tomorrow, since I just finished the Sound Waves chapter. Although I have a pretty good general idea of how waves work, I am stuck in one exercise that I can't seem to solve. The exercise says that:
By checking on a metal using an ultrasound device, the first mirrored signal was captured 12 micro-seconds after the sound was released into the metal, and the second signal was captured 30 micro-seconds after. Find how deep the defect is located and what's it's width.
I don't really understand how these devices work. Does the defect on the metal somehow stop the wave (maybe there is a vacuum created), slow it down (rust probably changes the speed), or is it something else?