(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

An atom initially at rest emits a photon with frequency f. Explain why the mass of the atom decreases, and by an amount greater than hf/c^2.

2. Relevant equations

E= mc^2

E = hf

3. The attempt at a solution

So I know that the atom must lose mass when the photon is emitted because in order for it to emit energy it must lose mass (by E = mc^2), but I don't understand why it should be more than hf/c^2, since from these 2 equations:

E = mc^2 = hf

therefore m = hf/c^2

Why is this wrong?

Thanks.

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# Homework Help: How much mass does an atom lose when it emits a photon?

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