Posted by Tim on April 29, 2014, 2:49 pm
Hello, I did excersice 10.1 and found that the sound velocity in a diatomic chain is v=a*sqrt(k/ (2*sqrt(Mm)) ). This seems to suggest that the density is p = 2*sqrt(Mm)/a, i.e. the effective mass is twice the geometric mean of the masses. Why do we use the geometric mean and not just the arithmetic mean, i.e. p=(M+m)/a ? 
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