AQA A Level Physics

Revision Notes

2.3.2 The Electromagnetic & Strong Force

The Electromagnetic Force

  • The electromagnetic force is only between charged particles
  • The exchange particle that carries this force is the virtual photon, γ
  • Properties of the photon are:
    • It has no mass
    • It has no charge
    • It is its own antiparticle
  • Electromagnetic interactions occur whenever two charged particles interact with each other
  • For example, when two charged particles, such as electrons, are repelled by each other, a virtual photon is exchanged between them to produce this repulsion

Electromagnetic Repulsion

Feynman diagram of electromagnetic repulsion between two electrons shown by the exchange of a virtual photon

  • The electromagnetic force is also responsible for binding electrons to atoms
    • This is due to the attractive force between the negative electrons and positive nucleus

Hadrons & The Strong Nuclear Force

  • Hadrons are particles that are made up of quarks
    • Hence they are subject to the strong interaction
  • The exchange particle of the strong interaction is either:
    • The pion (between nucleons)
    • The gluon (between quarks)
  • This means that leptons cannot interact with the strong force, since they are not made up of quarks

Hadrons & The Strong Force

Feynman diagram of the interaction between an up and down quark. The gluon is the exchange particle between them.

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