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What useful thing can happen to a wave when it encounters a concave reflecting surface?

The wave reflects off the surface and travels in the opposite direction from which it came.
The wave reflects off the surface and appears to be expanding out from a point behind the surface.
The wave reflects off the surface and is focused to a point called the focal point.
The wave reflects off the surface and diverges radially outward from the surface.

User Bunndan
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Answer:

Step-by-step explanation:

When a sound hits a surface, some energy is reflected, and some is absorbed. Smooth, hard surfaces reflect most sound, so you get echo in an empty room, for instance, whereas fill the room with furniture, put down a carpet and hang curtains and the sounds are dampened. Special surfaces on walls, ceilings and floors are used to dampen reflected sound in recording studios and audio laboratorie

Rock is hard and highly elastic, and when sound passes through it, the rock generally returns to the original state, with no record of the passage of sound. If the sound is intense enough, then a permanent record can be formed. That does happen when a shock wave (intense sound) passes through quartz crystals from asteroid impacts. Such "shocked quartz" was early evidence that the death of the dinosaurs was associated with a huge impact.

A related and fascinating story: Edward Purcell, great Harvard physicist, winner of the Nobel Prize, once speculated that sound waves could leave patterns in silk. As the silk worm extrudes the thread, the size of the thread might be affected by ambient sound. If right, he would be able to reconstruct ancient sounds and maybe even voices from people in the silk worm farms, from ancient silk! He did some careful experiments, but he couldn’t find anything that worked.

User Isaac Betesh
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