160 Questioning the Universe: Concepts in Physics
Rule 4: A statement of conservation of energy coupled with Einstein’s
hypothesis in his photoelectric effect paper that light has an energy given
by E = hf.
Rule 5: De nes what property of the motion (angular momentum) determines
the discrete levels.
When Bohr combined these rules, he was able to derive the value of the energy
of each allowed level. Knowing the energy, he then knew the energy difference
between each level. Using rule 4, he could then derive the frequency of the emitted
radiation. These frequencies had to be discrete, as was one of the heretofore mysteri-
ous observations. Even more importantly, his predicted frequencies agreed with the
already known measured frequencies. Ob