Sounds Waves and Index of Refraction

[bluedevil61212]

The explanation to AAMC test #7, physical science #22 says: "The index is a measure of the ratio of the velocity in air to the velocity in the medium. For sound the speed becomes greater because the speed of sound in a solid is much greater in air (the glass has stiff rigid bonds which gives rise to a speed more than 10 times greater than air)

Can someone explain this a bit more? Are there any other cases where a wave travels faster in a medium with a higher index of refraction?

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[gwjib04]

The explanation to AAMC test #7, physical science #22 says: "The index is a measure of the ratio of the velocity in air to the velocity in the medium. For sound the speed becomes greater because the speed of sound in a solid is much greater in air (the glass has stiff rigid bonds which gives rise to a speed more than 10 times greater than air)

Can someone explain this a bit more? Are there any other cases where a wave travels faster in a medium with a higher index of refraction?

Great question.

For light, a transverse wave, speed in gas>speed in liquid>speed in solid. Doesn't need the medium to propagate because its an electromagnetic wave.

For sound, a longitudinal wave, speed in solid>speed in liquid>speed in gas
Its periodic oscillations ARE the medium; fluctuations in air density is the defn of sound. It uses the restoring force of the medium to propagate.

BTW Speed of sound is a Bulk phenomenon, proportional to the square root of the Bulk modulus.Gases have smaller Bulk Moduli so sound is slower in gases.


Check out this link: http://www.physlink.com/education/askexperts/ae81.cfm

You can't hear in space but you can look back in time

 

[ClemsonFirst]

Right. So light does not need a medium because it is electromagnetic. When there is a medium, light and other EM waves will travel slower. Like when you are stuck in traffic on the interstate. All the other cars are the medium and you are the light wave.

Sound depends on a medium because sound is generated through the collision of the molecules in a particular fashion. When the molecules are closer together, like in a metal bar instead of air, they have to travel less distance to contact the next molecule, propagating the wave faster.

I'm assuming the video explains this but I didn't watch it. I just felt like writing it out.