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IB Physics: Fusion and stars — Practice Questions & Answers

280 practice questions available for this topic — here are 10 with full answers and explanations.

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Practice questions with answers

1 Multiple choice · Easy

Nuclear fusion is the process in which:

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WhyFusion joins light nuclei (such as hydrogen) into heavier ones (such as helium), releasing energy. It powers stars.
2 Multiple choice · Medium

In a main-sequence star such as the Sun, the dominant fusion process converts:

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WhyThe proton-proton chain fuses hydrogen nuclei into helium, releasing energy that supports the star.
3 Multiple choice · Medium

A main-sequence star is in equilibrium because:

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WhyGravitational collapse is balanced by the outward radiation (and gas) pressure from fusion, giving hydrostatic equilibrium.
4 Multiple choice · Easy

The luminosity of a star is defined as:

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WhyLuminosity is the total power (energy per second) radiated by the star across all wavelengths.
5 Multiple choice · Medium

On a Hertzsprung-Russell diagram, most stars lie along a band called the:

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WhyMost stars, including the Sun, spend their hydrogen-burning lifetime on the main sequence, the diagonal band on the HR diagram.
6 Multiple choice · Hard

Fusion requires extremely high temperatures mainly because the nuclei must:

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WhyHigh temperatures give nuclei enough kinetic energy to overcome their electrostatic (Coulomb) repulsion and get close enough to fuse.
7 Fill in the blank · Easy

The process that powers the Sun by joining light nuclei together is nuclear .

Answer: fusion

WhyNuclear fusion of hydrogen into helium releases the energy that the Sun radiates.
8 Fill in the blank · Medium

A stable star is in equilibrium between inward gravitation and outward radiation .

Answer: pressure

WhyHydrostatic equilibrium balances gravity against the outward pressure produced by fusion in the core.
9 Multiple choice · Hard

Star X has temperature T, luminosity L and radius R. Star Y has luminosity 4L and temperature 2T. What is the radius of Y?

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WhyL proportional to R squared T to the fourth. 4L = R_Y squared (2T) to the fourth / (R squared T to the fourth) gives R_Y squared = R squared/4, so R_Y = R/2.
10 Multiple choice · Medium

According to the Stefan-Boltzmann law, the luminosity of a star depends on its temperature raised to the power

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Whyfour (T to the fourth).

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Practise other IB Physics topics

Topic A.1 (SL/HL): Kinematics Topic A.2 (SL/HL): Forces and momentum Topic A.2 (HL): Forces and momentum Topic A.3 (SL/HL): Work, energy and power Topic A.4 (HL): Rigid body mechanics Topic A.5 (HL): Galilean and special relativity Topic B.1 (SL/HL): Thermal energy transfers Topic B.1 (HL): Thermal energy transfers Topic B.2 (SL/HL): Greenhouse effect Topic B.3 (SL/HL): Gas laws Topic B.3 (HL): Gas laws Topic B.4 (HL): Thermodynamics Topic B.5 (SL/HL): Current and circuits Topic C.1 (SL/HL): Simple harmonic motion Topic C.1 (HL): Simple harmonic motion Topic C.2 (SL/HL): Wave model Topic C.3 (SL/HL): Wave phenomena Topic C.3 (HL): Wave phenomena Topic C.4 (SL/HL): Standing waves and resonance Topic C.5 (SL/HL): Doppler effect Topic C.5 (HL): Doppler effect Topic D.1 (SL/HL): Gravitational fields Topic D.1 (HL): Gravitational fields Topic D.2 (SL/HL): Electric and magnetic fields Topic D.3 (SL/HL): Motion in electromagnetic fields Topic D.3 (HL): Motion in electromagnetic fields Topic D.4 (HL): Induction Topic E.1 (SL/HL): Structure of the atom Topic E.1 (HL): Structure of the atom Topic E.2 (HL): Quantum physics Topic E.3 (SL/HL): Radioactive decay Topic E.3 (HL): Radioactive decay Topic E.4 (SL/HL): Fission Topic E.5 (HL): Fusion and stars