Production of Elements (Oxford AQA IGCSE Physics)

Revision Note

Production of Elements

  • Fusion reactions in stars are their source of energy

    • They produce all of the naturally occurring elements in the Universe

    • These elements may be distributed throughout the Universe by the explosion of a massive star (supernova) at the end of its life

  • For main sequence stars with a mass larger than that of our Sun:

    • Hydrogen nuclei combine in nuclear fusion reactions to produce helium nuclei, releasing lots of energy in the process

    • Stars maintain their energy output for millions of years because of the large amounts of hydrogen available

    • Once all of the hydrogen has reacted, fusion slows and the star expands becoming a red supergiant

    • Helium nuclei are then fused to form carbon

    • Further fusion processes take place in which heavier nuclei are formed such as nitrogen and oxygen

    • Heavier elements up to iron are also formed

Forces on a main sequence star

Outwards and inwards forces are balanced in a stable main sequence star, for IGCSE & GCSE Physics revision notes
The outwards and inwards forces within a star are in equilibrium. The centre red circle represents the main sequence star's core and the orange circle represents the star's outer layers
  • Once the fusion reactions inside the red supergiant cannot continue, the core of the star will collapse suddenly

  • The outer layers are blown away in a gigantic explosion 

    • This is called a supernova

    • The temperatures in the explosion are so high that the heavier nuclei can fuse to create all the naturally occurring elements in the Universe

      • All elements heavier than iron are created in supernovae

    • The explosion disperses these elements out into space

  • The early Universe contained only hydrogen because fusion is needed to create heavier nuclei

    • Before stars formed there was no fusion

Forces on a red supergiant

A main sequence star becomes a red supergiant, for IGCSE & GCSE Physics revision notes
A main sequence star will expand into a red supergiant because hydrogen is used up in the centre, so it collapses. The cooler surface expands and it becomes redder.

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