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IB Physics SL E.5 Fusion and Stars Question Bank

Practise IB Physics SL E.5 by connecting fusion reactions, mass defect, stellar spectra and energy output.

Syllabus
First assessment 2025
Course
Physics SL
Level
SL

Exam points

  • Balance fusion equations and relate mass defect to released energy and nuclear stability.
  • Interpret stellar spectra, luminosity, temperature and wavelength evidence.
  • Explain how fusion powers stars and evaluate basic energy-transfer or safety claims.

Covered syllabus points

E.5.1—Stellar equilibriumE.5.2—Fusion in starsE.5.3—Fusion conditionsE.5.4—Stellar mass and evolutionE.5.5—HR diagram regionsE.5.6—Stellar parallaxE.5.7—Stellar radii

E.5 Fusion and stars question 1

[Maximum number: 6]

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

Figure for Question E.5 Fusion and stars 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}

Question (a)

(a)

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
[ 2 ]

Question (i)

(i)

Outline the role of fusion reactions in maintaining a stable radius of the Sun.

[ 2 ]

Question (b)

(b)

The positions of the Sun and the star Antares are shown in the Hertzsprung-Russell (HR) diagram.

Figure for Question (b) — IB Physics SL
[ 4 ]

Question (i)

(i)

State the star type of Antares.

[ 1 ]

Question (ii)

(ii)

Discuss how nuclear fusion processes in Antares are different from those in the Sun.

[ 3 ]

E.5 Fusion and stars question 2

[Maximum number: 3]

Three stars A, B and C are labelled on the Hertzsprung-Russell (HR) diagram. L⊙L_{\odot} is the Luminosity of the sun.

Figure for Question E.5 Fusion and stars question 2 — IB Physics SL

Question (a)

(a)

State the main element that is undergoing nuclear fusion in star C .

[ 1 ]

Question (b)

(b)

White dwarfs with similar volumes to each other are shown on the HR diagram.

Construct a line, on the HR diagram, to show the possible positions of other white dwarf stars with similar volumes to those marked on the HR diagram.

[ 2 ]

E.5 Fusion and stars question 3

[Maximum number: 4]

Star A is a main sequence star.

The data for Star A and the Sun are given in a table.

Table for Question E.5 Fusion and stars question 3 — IB Physics SL

Question (a)

(a)

State how physical stability is maintained in main sequence stars.

[ 1 ]

Question (b)

(b)

Explain why nuclear fusion in the core of the star occurs when the temperature and density exceed threshold values.

[ 2 ]

Question (c)

(c)

Calculate, in m , the distance to Star A from Earth.

[ 1 ]
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