Physics · Waves. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
When a wave meets the boundary between two materials it can be reflected, absorbed or transmitted. Usually some of each happens. How much depends on the two materials and on the wavelength.
Sound travels through a solid as vibrations of its particles. In the ear, sound waves make the eardrum and other parts vibrate, and this gives the sensation of sound. It works only over a limited range of frequencies.
Waves let us see where we cannot look. Ultrasound is partly reflected at each boundary, so the time for an echo gives the distance to the boundary. Seismic waves from earthquakes show what the inside of the Earth is like.
In echo questions students forget to halve. Speed × time is the distance there and back, so divide by 2 to get the depth.
Answer: 0.10 m (10 cm)
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