Cracking the SAT Physics Subject Test

and for other one-electron atoms—ionized helium (Z = 2), doubly-ionized lithium
(Z = 3), etc.—the energy levels are

where Z is the number of protons in the atom’s nucleus.

When an excited electron drops from energy level n = j to a lower one, n = i, the
transition causes a photon of energy to be emitted, and the energy of a photon is the
difference between the two energy levels:

Eemitted photon = |∆E| = Ej − Ei

Questions 4-5

Refer to the following diagram.