HSC Physics — Module 7
Emission Spectra — Flashcards & Quiz
Atomic emission spectra consist of discrete lines at specific wavelengths, and the Bohr model explains them through transitions between quantised energy levels where ΔE = hf. HSC Physics Module 7 asks you to calculate photon wavelengths using the Rydberg formula, identify the Balmer (visible), Lyman (UV) and Paschen (IR) series, and explain how emission and absorption spectra are used in astrophysics to identify stellar composition and red-shift.
Key Points
- Emission spectra consist of discrete wavelengths emitted when electrons fall from higher to lower energy levels: ΔE = hf = hc/λ.
- The Bohr model explains discrete lines through quantised orbits: only specific orbits (and therefore specific energy differences) are allowed.
- Hydrogen spectral series: Lyman (UV, to n=1), Balmer (visible, to n=2), Paschen (IR, to n=3); wavelengths calculated from the Rydberg formula 1/λ = R(1/n₁² − 1/n₂²).
- Emission lines appear as bright lines on a dark background (from a hot gas); absorption lines appear as dark lines on a continuous background (from a cool gas in front of a hot source).
- Astrophysics applications: spectral lines from distant stars identify stellar composition; red-shift of lines reveals recessional velocity (Hubble's law).
- Exam skill: given energy levels in eV (or Joules), calculate the photon wavelength of a specific transition and classify it as UV, visible, or IR.
Common Mistakes to Avoid
- Mixing up emission (hot gas emits) and absorption (cool gas absorbs) spectra.
- Forgetting the Bohr model: energy levels are quantised, transitions are discrete.
- Using the Rydberg formula with wrong n values — n₁ is the lower level, n₂ is the upper.
- Ignoring spectral series (Lyman UV, Balmer visible, Paschen IR) for hydrogen.
- Treating spectral lines as continuous bands — they're discrete because energy levels are discrete.
Exam Strategy
HSC Module 7 emission spectra questions ask you to (1) calculate wavelengths from energy levels, (2) identify spectral series, or (3) link to astrophysics. Method: (1) calculate ΔE from the Bohr model, (2) apply E = hf = hc/λ to get wavelength, (3) match wavelength to visible/UV/IR region, (4) for astrophysics, link to red-shift and stellar composition.
Sample Flashcards
Q1: What is an emission spectrum and how is it produced?
An emission spectrum is produced when excited atoms release energy as photons during electron transitions from higher to lower energy levels. Each element has a unique set of spectral lines (fingerprint). Hot gas → line spectrum. Hot solid/liquid → continuous spectrum.
Sample Quiz Questions
Q1: All elements produce identical emission spectra.
Answer: FALSE
Each element has unique energy levels, producing a unique emission spectrum (spectral fingerprint). This enables spectroscopic identification.
Revision Tip
Emission spectra calculations and series identification are drillable — use Revizi flashcards for hydrogen transitions until you can classify any n₁→n₂ into its series.
Related Concepts
Last updated: March 2026 · 1 flashcards · 1 quiz questions