# Derivation of De Broglie wavelength

by PhiJ
Tags: broglie, derivation, wavelength
 P: 41 The De Broglie wavelength was derived like this by our physics teacher. E=hf v=fλ E=mc^2 so hf=mc^2 hv=λmc^2 Then the WRONG BIT h=λmv h=λρ λ=h/ρ But that only works for light (when c=v). There must be a correct way of deriving it for electrons etc. We are expected to use this for electrons.
P: 1,135
 Quote by PhiJ The De Broglie wavelength was derived like this by our physics teacher. E=hf v=fλ E=mc^2 so hf=mc^2 hv=λmc^2 Then the WRONG BIT h=λmv h=λρ λ=h/ρ But that only works for light (when c=v). There must be a correct way of deriving it for electrons etc. We are expected to use this for electrons.
It only works if you take: wave-speed = [itex]\frac{c^2}{v}[/tex] where v is the physical
speed of the electron, this is however an ad-hoc assumption here. It's not
that hard to derive λ=h/ρ directly from E=hf but it takes Special Relativity:

http://www.chip-architect.com/physics/deBroglie.pdf

Regards, Hans

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