Edexcel IGCSE Physics 复习笔记 7.3.4 Nuclear Fusion

• Small nuclei can react to release energy in a process called nuclear fusion
• Nuclear fusion is defined as:

When two light nuclei join to form a heavier nucleus

• This process requires extremely high temperatures to maintain
  • This is why nuclear fusion has proven very hard to reproduce on Earth

   

• Stars, including the Sun, use nuclear fusion to produce energy
  • Therefore, fusion reactions are very important to life on Earth

   

• In most stars, hydrogen atoms are fused together to form helium and produce lots of energy

Two hydrogen nuclei are fusing to form a helium nuclei

• The energy produced during nuclear fusion comes from a very small amount of the particle’s mass being converted into energy
• Albert Einstein described the mass-energy equivalence with his famous equation:

E = mc²

• Where:
  • E = energy released from fusion in Joules (J)
  • m = mass converted into energy in kilograms (kg)
  • c = the speed of light in metres per second (m/s)

   

• The amount of energy released during nuclear fusion is huge:
  • The energy from 1 kg of hydrogen that undergoes fusion is equivalent to the energy from burning about 10 million kilograms of coal

   

Conditions for Fusion

Energy from Fusion

• 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
  • 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

   

• Fusion and fission reactions should not be confused
• We are able to use fission reactions on Earth as a source of energy for producing electricity
• However, the temperatures required to maintain fusion reactions means that it is not yet a commercially viable method for generating electricity
• If however it were possible, then fusion would have a number of advantages over fission:
  • Fusion reactions would be capable of producing even more energy than fission reactions
  • The fuels required for fusion reactions are more plentiful than the Uranium and Plutonium used in fission reactors
  • The products of nuclear fusion are much safer, with very little long term radioactive waste produced, and the risk of a dangerous accident at a fusion reactor is much lower than in a fission reactor

   

• The following table summarises some of the key differences between fusion and fission:

Comparison of Nuclear Fusion and Fission Table