IB Physics SL E.5 Fusion & stars Question Bank

Practise explaining stellar fusion and equilibrium, tracing mass-dependent evolution and using HR diagrams, parallax and luminosity–temperature data to determine stellar…

Syllabus
First assessment 2025
Topic
—
Level
SL

Exam points

  • explain stellar equilibrium and fusion thresholds using pressure balance, high temperature and density
  • calculate fusion energy, reaction rate or main-sequence lifetime from luminosity, fuel mass and mass defect
  • predict mass-dependent stellar evolution, nucleosynthesis pathways and final white-dwarf or supernova remnants
  • interpret HR-diagram regions and paths, then use L=4πR²σT⁴ or constant-radius lines to compare radii
  • use parallax angle and d(pc)=1/p(arcsec) with unit conversions to determine stellar distance

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: 3]

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
[ 1 ]

Question (i)

(i)

State the star type of Antares.

[ 1 ]

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: 3]

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 ]
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