# Derivation of de Broglie's Equation

I came across the derivation, present all across the web, which utilized Einstein's energy mass equivalence equation and energy of a photon. It goes like this: $$E = mc^2,\;\;E = h f \;\;[f = \text{frequency} ]\;\;\Rightarrow \;\;hf = mc^2\\ \frac{h c}{\lambda} = mc^2 \;\;[\lambda = \text{wavelength}]\\ \frac{h}{\lambda} = p, \;\;\;\frac{h}{p} = \lambda,\;\;\;\frac{h}{mv} = \lambda$$ With this, I have a problem with every step (like converting $mc$ to $p$ and then to $mv$)? IS this really correct? How?

Supposing we use, $E/c = p$ for a photon, then isn't it still wrong? Aren't we using EM radiation to find an associated wave? Aren't these completely different? Could someone please help with the real one?

• Hi and welcome to Physics SE. Please find info on tex-ing and mathjax here: physics.stackexchange.com/help/notation. It's really easy actually. – udrv Feb 29 '16 at 6:08
• Oh, Thank you, I will take a look! I really want an answer, though... – Adam Karlson Feb 29 '16 at 6:30
• Came across where? – Qmechanic Feb 29 '16 at 8:09
• @Qmechanic Googled "De Broglie equation Derivation " and got many results exactly like the one above, including images – Adam Karlson Mar 1 '16 at 6:57