Pick a wavelength and fire photons at the atom. A photon is absorbed only when its energy exactly matches a jump between levels; the electron then falls back down, giving off photons that land on the spectrometer. Speeds and sizes are not to scale.
Work functions are typical textbook values in electron volts (1 eV = 1.602 × 10−19 J). Real surfaces vary a little.
Pick Spin up or Spin down, then tap (or press Enter on) a box, or drag the piece onto a box. Remove takes the last electron out of a box. Boxes are stacked by energy: lowest at the bottom.
Your job
The worked solution animates after a correct answer or when you ask for it: the set-up builds term by term and units cancel with a red strike.
Wrong picks are fine here. Each one tells you why.