Hydrogen Spectrum (Bohr Model)

PHY-118 · Semester I · Physics

intermediate25 minAvailable

Hydrogen spectrumBohr model · Eₙ = −13.6/n² eV

Spectrum (Lyman 91 → Balmer → Paschen 1875 nm)

91 nm (Lyman)656 nm (Hα)1875 nm (Paschen)

Lab brief

Objective

Excite the electron in a hydrogen atom and observe the exact spectral lines it emits as it cascades down the energy levels.

Theory & concepts

The Bohr model quantizes the electron's energy: it can only sit in discrete levels En = -13.6/n² eV. An electron jumps between levels by absorbing or emitting a photon whose energy exactly equals the level difference. Every allowed transition therefore produces a specific wavelength — a spectral line.

Rendering diagram…

Transitions between hydrogen energy levels

The series

Transitions that end at n=1 form the Lyman series (ultraviolet), those ending at n=2 the Balmer series (visible), and those ending at n=3 the Paschen series (infrared).

Prerequisites

Topic: Bohr atom and the spectrum of hydrogen

Instructions

1Click an upper level to excite the electron (or use the excitation buttons).
2Watch the electron drop through allowed transitions, emitting a photon each step.
3Check the spectral lines that accumulate on the spectrum strip below.
4Filter by series — Lyman, Balmer or Paschen — and compare the wavelengths.
5Read the exact wavelength of each emitted line from the list.

Tasks

Balmer lines
Excite to n=3, 4 and 5 and record the three visible Balmer wavelengths.
Biggest jump
Which transition emits the highest-energy photon? Which has the shortest wavelength?
Direct vs cascaded
Compare emitting one photon from n=4 to n=1 versus stepping through intermediate levels.
Series filter
Confirm Lyman lines are more energetic than Balmer lines.

Self-check

Emitted wavelengths match the level differences via E = hc/λ.
The Lyman/Balmer/Paschen series are correctly identified.
The student explains why cascade paths still conserve total energy.
The student reads and interprets exact line wavelengths.

Environment

energy level diagramelectron excitationphoton emissionspectrum stripseries filters