CIE AS Physics (9702) 2019-2021

Revision Notes

13.2.2 Quark Composition

Quark Composition: Protons & Neutrons

  • Protons and neutrons are not fundamental particles. They are each made up of three quarks
  • Protons are made up of two up quarks and a down quark
  • Neutrons are made up of two down quarks and an up quark

 

Quarks in proton and neutrons, downloadable AS & A Level Physics revision notes

Protons and neutrons are made up of three quarks

 

  • You will be expected to remember these quark combinations for exam questions

 

Worked example

Worked example - quarks in an element, downloadable AS & A Level Physics revision notes

  • Step 1: Calculate number of protons:
    • The number of protons is from the proton number = 26 protons
  • Step 2: Calculate number of neutrons:
    • The number of neutrons = nucleon number – proton number = 56 – 26 = 30 neutrons
  • Step 3: Up quarks in a proton:
    • Protons are made up of uud quarks = 2 up quarks
  • Step 4: Up quarks in a neutron:
    • Neutrons are made up of udd quarks = 1 up quark
  • Step 5: Total number of up quarks:
    • 26 protons x 2 up quarks = 52 up quarks
    • 30 neutrons x 1 up quark = 30 up quarks
    • 52 + 30 = 82 up quarks

Quark Composition: β– & β+ decay

  • Beta decay happens via the weak interaction
    • This is one of the four fundamental forces and it’s responsible for radioactive decays

Quark Composition: β decay

  • Recall that β decay is when a neutron turns into a proton emitting an electron and anti-electron neutrino
  • More specifically, a neutron turns into a proton because a down quark turning into an up quark

Beta minus decay quarks, downloadable AS & A Level Physics revision notes

Beta minus decay is when a down quark turns into an up quark

Quark Composition: β+ decay

  • Recall that β+ decay is when a proton turns into a neutron emitting an positron and an electron neutrino
  • More specifically, a proton turns into a neutron because an up quark turns into a down quark

 

Beta plus decay quarks, downloadable AS & A Level Physics revision notes

Beta minus decay is when an up quark turns into a down quark

Worked example

Worked example - beta decay quarks, downloadable AS & A Level Physics revision notes

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