Syllabus Edition
First teaching 2023
First exams 2025
Properties of Quarks (Cambridge (CIE) A Level Physics)
Revision Note
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 quarks
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:
The equivalent antiparticle of the quark is the anti-quark
These are identical to quarks except with opposite relative charges
Anti-quarks
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 =
The other quark combinations add up to either 0 or −1
A: Up, strange, strange =
C: Top, anti-up =
D: Anti-up, anti-up, anti-strange
Remember that anti-particles have the opposite signs
Examiner Tips and Tricks
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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