A LevelPhysicsCIERevision Notes11. Particle Physics11.2 Fundamental ParticlesProperties of Quarks

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First teaching 2023

First exams 2025

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Properties of Quarks (CIE A Level Physics)

Revision Note

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Properties of quarks

  • The charge of a hadron is determined by the sum of the charges of its quarks
  • Each flavour of quark has a certain relative charge:

 Relative charge of quarksCharge of quarks, downloadable AS & A Level Physics revision notes

Each flavour of quark has a charge of either +⅔e or -⅓e

  • For example, a proton is made up of two up quarks and a down quark. Adding up their charges gives the charge of a proton:

uud space equals space straight p

plus 2 over 3 space plus 2 over 3 space minus 1 third space equals space plus 1 e

  • The equivalent antiparticle of the quark is the anti-quark
  • These are identical to quarks except with opposite relative charges

Anti-quarks

Charge of anti-quarks, downloadable AS & A Level Physics revision notes

Each flavour of anti-quark has a charge of either -⅔e or +⅓e. The quark composition of anti-protons and anti-neutrons changes to anti-quarks

Worked example

Particles are made up of a combination of three quarks or two quarks. Which quark combination would not give a particle a charge of -1 or 0?

A. up, strange, strange

B. charm, charm, down

C. top, anti-up

D. anti-up, anti-up, anti-strange

Answer: B

  • Add up the charge of the individual quarks
    • Charm, charm, down = 2 over 3 space plus space 2 over 3 space minus space 1 third space equals space plus 1
  • The other quark combinations add up to either 0 or −1
    • A: Up, strange, strange = 2 over 3 space minus space 1 third space minus space 1 third space equals space 0
    • C: Top, anti-up = plus 2 over 3 space minus 2 over 3 space space equals space 0
    • D: Anti-up, anti-up, anti-strange negative 2 over 3 space minus 2 over 3 space plus space 1 third space equals space minus 1
      • Remember that anti-particles have the opposite signs

Examiner Tip

You will be expected to remember the charge of each quark. However, instead of memorising the charges of anti-quarks too, just remember they are identical but with opposite signs.

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    Leander

    Author: Leander

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    Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.