The angular frequency of vibrations in a one-dimensional monatomic crystal are given by where w(k) = 4K m sin k = ka 2 2π X is the wavenumber of the vibration pattern in terms of its wavelength >, the spring constant between neighbouring atoms, and m the mass of each atom. (i) Show that the frequency does not change if one shifts 2π k→ k +-. a (ii) Briefly explain the physical reason for this periodicity.

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The angular frequency of vibrations in a one-dimensional monatomic crystal are given by
where
w (k)
=
4K
m
sin
k =
ka
2
2π
λ
is the wavenumber of the vibration pattern in terms of its wavelength >, the spring constant
between neighbouring atoms, and m the mass of each atom.
(i) Show that the frequency does not change if one shifts
2π
k→ k +.
a
(ii) Briefly explain the physical reason for this periodicity.
Transcribed Image Text:The angular frequency of vibrations in a one-dimensional monatomic crystal are given by where w (k) = 4K m sin k = ka 2 2π λ is the wavenumber of the vibration pattern in terms of its wavelength >, the spring constant between neighbouring atoms, and m the mass of each atom. (i) Show that the frequency does not change if one shifts 2π k→ k +. a (ii) Briefly explain the physical reason for this periodicity.
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