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

lotus0618
Posts: 182
Joined: Sun Dec 29, 2019 5:47 pm

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

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?
NS_Tutor_Mathias
Posts: 616
Joined: Sat Mar 30, 2019 8:39 pm

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

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.