OCR A Level Physics

Revision Notes

6.8.2 Hadrons & Leptons

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Subatomic Particles

  • Subatomic particles can be divided into two families:
    • Hadrons
    • Leptons


  • Hadrons are affected by the strong nuclear force
  • They are made of quarks
  • Include:
    • Protons
    • Neutrons
    • Mesons
    • and their corresponding antiparticles
  • If charged they experience the electromagnetic force
  • Decay occurs by the weak nuclear force

  • The large hadron collider at CERN (LHC) is used to look inside fundamental particles



  • Are fundamental particles
    • Fundamental particles have no internal structure
    • They cannot be divided or split into smaller parts
    • This is because they are not composed of quarks
  • Leptons are not affected by the strong nuclear force 
  • There are 6 leptons that include:
    • Electrons
    • Neutrinos
    • Muons
  • If charged they experience the electromagnetic force


Leptons, downloadable AS & A Level Physics revision notes

The six leptons are all fundamental particles

  • The muon and tau particle are very similar to the electron but with slightly larger mass
  • Electrons, muon and tau particles all have a charge of −1e and a mass of 0.0005u
    • u is the unified atomic mass unit
    • It has the value 1.661 × 10−27 kg
  • There are three flavours (types) of neutrinos
    • The electron neutrino, νe
    • The muon neutrino, νμ
    • The tau neutrino, ντ
  • Neutrinos are the most abundant leptons in the universe
    • They have no charge and negligible mass (almost 0)
  • Neutrinos are produced in particle interactions which also involve the other leptons
    • For example, if an electron is produced in a particle interaction, an electron neutrino will also be produced
  • Leptons interact through the weak interaction, electromagnetic force and gravitational forces
  • However, they do not interact with the strong force
    • Although quarks are fundamental particles too, they are not classed as leptons
    • Leptons do not interact with the strong force, whilst quarks do

Worked example

Circle all the anti-leptons in the following decay equation. WE - Leptons question image, downloadable AS & A Level Physics revision notes

Worked example - leptons, downloadable AS & A Level Physics revision notes

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