The Conditions for Fusion (Edexcel GCSE Physics)

• Since protons have a positive charge, they repel each other
  • In order to overcome this repulsion, the protons must have very high kinetic energy in order to be travelling towards each other at very high speeds

The fusion of two protons is only possible through high temperature and pressure

• In order to make the molecules of a gas travel at such speeds, the gas has to be heated to millions of degrees Celsius – a temperature that is usually only reached at the centre of a star
• In regular conditions, i.e. on Earth, the possibility of collisions between nuclei which result in fusion is very low
  • In order to increase the number of collisions (and hence fusions) that occur between nuclei, high densities (and hence pressures) are also needed

• The conditions for fusion are:
  • Very high temperature of fuel
  • Very high kinetic energy / speed of nuclei to overcome repulsion
  • Very high density / pressure to increase the possibility of suitable collisions

• The main reasons why fusion is not currently used as a source of power on Earth are the difficulties in achieving (and maintaining)
  • High temperatures
  • High pressures

• Whilst physicists have been able to attain the temperatures and pressure needed, there are difficulties in containing them, which inevitably means that only a small amount of fusion can take place
  • Such a small rate of fusion is not useful for current energy needs

• Creating the temperatures needed for fusion requires a great deal of energy
  • Hence, physicists are still a long way from the point where they will produce more energy from fusion than the energy needed to start it

ANSWER:  B

• • • Hydrogen nuclei have positive charges
    • So two hydrogen nuclei would have a repulsive force between them
    • There exists a repulsive force between protons that has to be overcome for hydrogen fusion to happen

  

  Hydrogen ions are protons, and their positive charge makes them repel one another

  • High temperatures are required to give the nuclei enough energy to overcome the repulsive force
  • The answer is not A because the products of the hydrogen fusion shown in the reaction is helium
    • Helium is an inert gas

  • The answer is not C because hydrogen is a very abundant element
    • It is the most common element in the universe

  • The answer is not D because hydrogen fusion would produce a huge amount of energy