## OCR A Level Physics

### Revision Notes

#### Subatomic Particles

• Subatomic particles can be divided into two families:
• 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

## Leptons

#### Leptons

• 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 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.   ### Get unlimited access

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