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MCAT Physics Question — Distress Signals

Distress signals in the form of light and sound are emitted from a submerged submarine. When the signals enter the atmosphere, what happens to the speed of sound and light, respectively?


A) The speed of sound and light both increase
B) The speed of sound and light both decrease
C) The speed of sound increases and the speed of light decreases
D) The speed of sound decreases and the speed of light increases




This question is testing your understanding of optical properties and characteristics of sound. Light travels faster in less dense mediums. Therefore, when light goes from water to air, it speeds up. Oppositely, sound travels faster in more dense mediums, which can be represented by the equation vsound = (B/ρ)1/2, where B is the bulk modulus and ρ is the density of the medium. While the ρgas < ρliquid < ρsolid, the Bgas << Bliquid << Bsolid. Therefore, vsolid > vliquid > vgas. Since the sound waves are travelling from liquid to gas, they will slow down making D the correct answer.


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