1. The problem statement, all variables and given/known data With the atomic clock a second is defined as the time it takes for EM radiation to oscillate 9192631770 times, which equals the energy gap between two energy levels of a caesium-133 atom. Note: it's a translation and the term used with the oscillation is "oscillation periods" 2. Relevant equations Calculate the energy difference (in eV) 3. The attempt at a solution At first I took the expression "oscillation periods" to mean that I had to use the T=1/f relation and insert it in the E=hf equation. However since T is in seconds and f means turns or oscillations, I went with f=9192631770. So, I have: E = hf = 6.626*10^(-34) Js * 9192631770 /s = 6.091*10^(-24) J = 3.8 * 10^(-5) eV I just hope to check whether I made the right assumptions and conversions, thank you.