O-LevelPhysicsNuclear Physics5054/21 · Oct/Nov 2024 · Q910 Marks

A stable star in a distant galaxy has a mass that is more than 15 times the mass of the Sun.

(a)(i)State the name of the nuclear reaction that occurs at the centre of the star and describe this nuclear reaction.[3]
(a)(ii)Explain how this nuclear reaction helps to keep the star stable.[3]
(b)As a massive star approaches the end of its life, it stops being stable and becomes a red supergiant.
(b)(i)State why the nuclear reaction can no longer keep the star stable.[1]
(b)(ii)Describe what then happens to the red supergiant.[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

[B1] (nuclear) fusion
[B1] hydrogen (nuclei) join / fuse together
[B1] to produce helium (nuclei)
[B1] reaction / it transfers energy thermally
[B1] (high temperature) produces (high) pressure / outward force
[B1] (inward) gravitational force balanced or (further) gravitational collapse prevented
[B1] not enough hydrogen (left) or runs out of hydrogen
[B3] any three from: (it / red supergiant) explodes turns into a supernova produces heavy elements forms a nebula leaves behind a neutron star / black hole

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