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### Sound wave is constant, but changes through medium?

Posted: Tue Jan 14, 2020 8:33 pm
I had some time to reflect on what I learned from the sound topic (harmonics, waves, sounds, etc.) Say for example, a sound wave propagates through a solid rod and exits into air. Obviously, the wavelength in solid is greater than wavelength in air (due to sound travels faster in solid). f is constant cause it depends on only the source.
Here is the part that i'm confused: you know how we have the velocity of soudn wave = 343 m/s. It's a constant velocity but here in this situation the sound wave velocity changes. Same for EM light wave's v = 3*10^8 m/s.
So correct me if i'm wrong, but the velocity of sound wave or light is constant within the medium, but will change across different medium depending on the index of refraction?

### Re: Sound wave is constant, but changes through medium?

Posted: Thu Jan 16, 2020 12:22 am
Right, with a few small caveats:
343 m/s is the speed of sound in air. It is faster in most other media, but you aren't required to know of any mathematical relationship about how much faster.

3*10^8 m/s is the speed of light (meaning all EM waves) in a vacuum. It is lower in ALL other media, in proportion to the index of refraction (so the higher the index of refraction, the lower the speed of light in that medium).

Sound requires a medium to propagate, so it will not travel in a vacuum at all. EM waves can propagate without a medium.