AQA GCSE Physics

Revision Notes

8.1.3 Fusion in Stars

Fusion in Stars

  • All the naturally occurring elements, apart from hydrogen, have been formed by nuclear fusion in stars
  • Nuclear fusion occurs when two light nuclei collide at high speed and join to create a larger, heavier nucleus
  • When the Universe was first formed, 13.8 billion years ago, the only element present was hydrogen
  • If two hydrogen nuclei collide with enough energy they will fuse into a helium nucleus
    • For example, the nuclei of two different isotopes of hydrogen (protium and tritium) can join to form a helium nucleus by the process of nuclear fusion

Fusion of Hydrogen, downloadable IGCSE & GCSE Physics revision notes

An example of the fusion of protium and tritium to form helium

  • The process of nuclear fusion releases energy
    • The energy is released in the form of heat and light

Exam Tip

When you are answering questions about nuclear fusion remember it is only the nuclei which combine. Do not write about atoms.

The Formation of New Elements

  • During the majority of a star’s lifetime, hydrogen nuclei fuse together to form helium nuclei
  • As the star runs out of hydrogen, other fusion reactions take place forming the nuclei of other elements
  • For example, two helium nuclei (produced by the fusion of 2 hydrogen nuclei) could fuse together to form a beryllium nucleus

Two helium nuclei fusing together to form a beryllium nucleus

  • The beryllium nucleus could then fuse with a helium nucleus to form a carbon nucleus

A beryllium nucleus fusing with a helium nucleus to form a carbon nucleus

  • Elements lighter than iron are formed in fusion reactions like the ones above

Formation of Elements Heavier than Iron

  • Elements heavier than iron are produced in supernovae explosions
    • A supernova occurs at the end of a massive stars life
    • When the star explodes it releases very large amounts of energy and neutrons
  • All of the elements which have been produced by the fusion reactions get thrown out and combine with the neutrons to form heavier elements

Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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