Electrons in an atom occupy discrete energy levels. A jump down emits a photon; a jump up absorbs one, with hf = E₁ − E₂. Because the levels are fixed, only certain photon energies appear, giving a line spectrum. Pick two hydrogen levels and read off the wavelength of the line.
MissionMake a visible line: drop an electron to n = 2 from n = 3, 4 or 5 (the Balmer series) and find its colour.Streak 0Best 0
Why does a hot gas emit only certain wavelengths (a line spectrum)?
transitionn = 3 → n = 2
energy gap ΔE1.89 eV
frequency f = ΔE/h4.57 × 10¹⁴ Hz
wavelength λ = hc/ΔE656 nm
regionvisible (red)
A jump down emits a photon carrying exactly the energy gap.