Speed of Sound in H2
Our Physics teacher asked me to forward the following to you
Our textbook gives the following values for the speed of sound
in air. 342 m/s
in H2 1339 m/s
in O2 316 m/s and in general the more dense the medium
the faster the speed . H2 is not in line with the pattern...Why?
Yes it is in line: for gases, the more dense the medium in terms
of mass per unit volume (at constant pressure), the SLOWER the
speed of sound. Pure O2 is actually heavier than air (which is
mostly N2) while H2 is much much lighter. The reason is that the
lighter a molecule is, the faster it moves (at given temperature),
and the speed of sound in gases is simply proportional to the speed
(on average) of the molecules.
Sound speed following density is an often quoted fact that is
really not followed by nature. The speed in solids is determined
by the elastic constants of the material which have very little
relation to density - they are more directly related to the
strength of the bonding between the atoms of the material, so that
a very strongly bonded material has a faster sound speed.
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Update: June 2012