1. The problem statement, all variables and given/known data The energy of the electron in the first and forth levels in a hydrogen atom are: (21.76*10^-19), (-0.85) e.V.. the electron moved from the forth level to the first level with one leap. Calculate: The frequency of the emitted photon from the atom 2. Relevant equations ΔE = hf 3. The attempt at a solution f = ΔE / h f = [(-0.85) - (21.76*10^-19)] / 6.6*10^-34 f = -1.2878*10^33 Hz .. I get that answer while the answer given in the book is 3.09*10^15 Hz, I'm confused..