P2.6.2 - AQA GCSE Physics Unit 2

P2.6.2	Nuclear fusion
	a) Nuclear fusion is the joining of two atomic nuclei to form a larger one.
	b) Nuclear fusion is the process by which energy is released in stars.
	c) Stars form when enough dust and gas from space is pulled together by gravitational attraction. Smaller masses may also form and be attracted by a larger mass to become planets.	Candidates should be able to explain why the early Universe contained only hydrogen but now contains a large variety of different elements. The term 'radiation pressure' will not be required.
	d) During the 'main sequence' period of its life cycle a star is stable because the forces within it are balanced.
	e) A star goes through a life cycle. This life cycle is determined by the size of the star.	Candidates should be familiar with the chart below that shows the life cycles of stars.
	f) Fusion processes in stars produce all of the naturally occurring elements. These elements may be distributed throughout the Universe by the explosion of a massive star (supernova) at the end of its life.	Candidates should be able to explain how stars are able to maintain their energy output for millions of years. Candidates should know that elements up to iron are formed during the stable period of a star. Elements heavier than iron are formed in a supernova.