De Broglie wavelength and particle momentum
A momentum state has a spatial wave phase.
Key knowledge
For a free-particle plane-wave component in a stated frame, momentum p=ħk and nonzero momentum magnitude gives wavelength λ=h/|p|. Massive particles can show interference/diffraction; their wavefunction is not a classical material string. A localized wave packet contains a spread of momenta and does not have one exact wavelength.
Values and equations
p=ħk; λ=h/|p|
- p
- Free-particle momentum vector kg m s⁻¹
- k
- Wavevector rad m⁻¹
- ħ,h
- Reduced and ordinary Planck constants J s
- λ
- Spatial wavelength for |p|>0 m
Conditions and scope
- Use canonical momentum for a free particle; external vector potentials distinguish canonical and kinetic momentum.
- A single wavelength characterizes a plane-wave component, not every localized state. Nonrelativistic p≈mv is a low-speed approximation; the matter-wave phase speed is not a signal speed.
Sources · 1
References
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Evidence and review
Read §6.5 de Broglie wavelength relation6.54 and wavevector/frequency relations6.55–6.56, phase-speed distinction and Davisson–Germer electron-diffraction interpretation. Restrict the equation to plane-wave components/free canonical momentum rather than assigning one wavelength to every wave packet.
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