IB Physics SL C.5.4 Spectral Line Shifts

Practise comparing observed and laboratory spectral lines to identify redshift or blueshift, calculate radial speed and infer whether a star or galaxy approaches or recedes.

Syllabus
First assessment 2025
Objective
—
Level
SL

Exam points

  • match an observed absorption or emission line to its laboratory rest wavelength before measuring the shift
  • identify redshift from longer observed wavelength and blueshift from shorter observed wavelength
  • calculate line-of-sight speed from Δλ/λ and state the corresponding approach or recession

C.5.4—Spectral line shifts question 1

[Maximum number: 1]

The Hubble constant is 2.3×10−18 s−12.3 \times 10^{-18} \mathrm{~s}^{-1}.

Outline how observations of spectra from distant galaxies provide evidence that the universe is expanding.

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