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IB Physics SL E 1 6 Spectra and Composition Questions

Use SL stellar spectra to identify chemical composition, matching absorption lines with laboratory spectra and explaining what star light reveals.

Syllabus
First assessment 2025
Course
Physics SL
Level
SL

Exam points

  • explain that absorption or emission lines occur at element-specific wavelengths and can identify elements in a star or nebula
  • describe how to obtain a laboratory line spectrum and compare it with stellar absorption or emission lines to determine composition
  • interpret stellar spectra and line positions to support conclusions about hydrogen, other elements and the composition of astronomical objects

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Study E.1.6—Spectra and composition conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Physics SL E 1 6 Spectra and Composition Questions question 1

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The diagram shows a simplified energy-balance model for the Earth surface–atmosphere system.

Figure for Question IB Physics SL E 1 6 Spectra and Composition Questions question 1 — IB Physics SL

The following data are given:

 Average albedo of Earth =0.30 Average global temperature of the surface =288 K Average Earth-Sun distance =1.5×1011 m\begin{aligned} \text { Average albedo of Earth } & =0.30 \\ \text { Average global temperature of the surface } & =288 \mathrm{~K} \\ \text { Average Earth-Sun distance } & =1.5 \times 10^{11} \mathrm{~m} \end{aligned}

The primary energy source of the Sun is the proton-proton (p-p) chain of fusion reactions. Four protons and two electrons produce a helium nucleus together with neutrinos and gamma photons. The overall reaction is:

411p+2−10e→24He+200ve+4γ4{ }_{1}^{1} \mathrm{p}+2{ }_{-1}^{0} \mathrm{e} \rightarrow{ }_{2}^{4} \mathrm{He}+2{ }_{0}^{0} v_{e}+4 \gamma

Outline how the presence of helium in the Sun can be confirmed empirically.

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