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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?

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The ultrasound gets reflected at a boundary.
In this case at the top and the bottom of the flaw where there is an air?/metal boundary.
It is an echo range finder.

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  • $\begingroup$ Okay, firstly thank you for helping me. So the wave travels at the defect and returns (get's reflected) for 12 microseconds (because it takes less time for the wave to return). And at the 30 microseconds margin we get the full width of the metal? That means it takes approx 15 microseconds for the wave to reach the end of the metal? If so i can find how deep the defect is located, but i have no clue how to find the width of the defect. Can you give some more information? $\endgroup$
    – Teabx
    May 11, 2017 at 18:53
  • $\begingroup$ In this case the width means top to bottom. It takes ultrasound 12 microseconds to travel from the source of microwaves to the top of the flaw and back to the detector which is adjacent to the source. $\endgroup$
    – Farcher
    May 11, 2017 at 19:06
  • $\begingroup$ I see. I think i got the wrong idea of the width, as i was thinking of horizontal length instead of vertical length, and that's where i was getting confused. Thank you for clearing it up for me. Have a great day :) $\endgroup$
    – Teabx
    May 11, 2017 at 19:12
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http://www.olympus-ims.com/sv/applications-and-solutions/introductory-ultrasonics/introduction-flaw-detection/

Luckily companies which make the equipment explain the science behind it.

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