Light Waves vs Sound Waves

[MedPR]

This is kind of a two part question (maybe more, I'm not sure).

1. Why does sound travel faster in glass compared to air, but light travels slower in glass compared to air? I know it has something to do with transverse vs logitudinal, but I would like to know a little more than "just because".

2. I remember reading that there are 3 (?) properties that increase the rate of sound wave travel. One being the bulk modulus (hence why sound travels faster in solids than gases). What are the other two?



Thanks!

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[Danlee07]

Sound is a mechanical wave so the medium's density and elastic properties are going to change the speed of sound. I forget the name of the rule, but there is a relationship between velocity and square root of tension of a medium. Glass has a higher density than air, which means a higher elasticity and compression can take place. Light is electromagnetic so it's a transverse wave which just depends on EM properties.

This part isn't really science-y but it's worked so far... I think of transverse like this: some arbitrary gas has a collision rate, but is traveling farther and faster than a solid state material. Because light is in both an electric and magnetic field, the light bounces from gas particle to gas particle (in this case, air) so it can go farther and faster than in a solid where it just bounces from one neighboring particle to another.