I saw a proof in a book for the de broglie equation which I thought was wrong.(adsbygoogle = window.adsbygoogle || []).push({});

if l = lambda, so wavelength and then all other notation is standard they said:

E=mc^2

E=hf

therefore,

mc^2=hf

but for a photon, c=v

so:

mv^2=hf

but mv=P

so:

Pv=hf

and v=fl

so:

Pfl=hf

Pl=h

and finally:

l=h/P

Anyway, that's what they said. But I thought since a photon doesn't have a mass "mv" couldnt be its momentum. Or does it not matter?

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# Proof of de broglie equation?

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