# Energy of a photon emission or absorbtion

1. Oct 14, 2012

### DODGEVIPER13

1. The problem statement, all variables and given/known data
When energy is absorbed is the E value negative and when the energy is emitted is the E value positive?

2. Relevant equations
E=hf=E1-E2 (Is this equation correct for noth emision and absorbtion or just absorbtionbecause this is what my textbook says)
E=-13.6/n^2

3. The attempt at a solution
I realize that when an electron drops from a excited state, the electron emits EM radiation. In the reverse process the electron absorbs energy. So if I use the equations I provided above I would always get a negative number and it also would make it look like energy absorbtion. However if I reverse the equation and make it look similar to the others I have found online E=hf=E2-E1 and apply the second equation to it I will get a positive number,and it will emit. So my question is does the equation alternate when looking at absorbtion and emission, if not is the equation in my book wrong and if its not then is my therory correct that negative means absorbtion and positive means emission.

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