On a couple of webisites I have seen that they have equated E=mc^2 with E=hf .... i.e hf=mc^2(adsbygoogle = window.adsbygoogle || []).push({});

But how can this be done when E=hf is describing the energy of a photon and E=mc^2 isnt?

Also, can someone provide me with a derivation of de Broglie’s theorem ?

Wavelength = h/momentum

thank you

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# Photon energy

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