Retrieval Practice
Quarks, Leptons & Conservation Laws — AQA A-Level Physics
Q1. What is the difference between a hadron and a lepton?
- Hadrons are made of quarks and experience the strong force.
- Leptons are fundamental (not made of quarks) and do not experience the strong force.
Q2. What is the difference between a baryon and a meson?
- A baryon is made of 3 quarks (baryon number = +1).
- A meson is made of a quark-antiquark pair (baryon number = 0).
Q3. State the quark composition and charge of (a) a proton and (b) a neutron.
(a) Proton = uud, charge = +2/3 +2/3 −1/3 = +1. (b) Neutron = udd, charge = +2/3 −1/3 −1/3 = 0.
Q4. State the charge, baryon number and strangeness of the up, down and strange quarks.
- Up: Q = +2/3, B = +1/3, S = 0.
- Down: Q = −1/3, B = +1/3, S = 0.
- Strange: Q = −1/3, B = +1/3, S = −1.
Q5. Which quark transformation occurs in β⁻ decay?
A down quark changes to an up quark (d → u), converting a neutron into a proton.
Q6. Which quark transformation occurs in β⁺ decay?
An up quark changes to a down quark (u → d), converting a proton into a neutron.
Q7. State the four quantities that must be conserved in all particle interactions.
Charge (Q), baryon number (B), lepton number (L), and energy/momentum.
Q8. When does strangeness not need to be conserved?
- In weak interactions.
- Strangeness can change by 0, +1 or −1 in a weak interaction.
Q9. State the quark composition of π⁺ and K⁺.
- π⁺ = ud̄ (up + anti-down).
- K⁺ = us̄ (up + anti-strange).
Q10. What is the baryon number of (a) a baryon, (b) an antibaryon, and (c) a meson?
(a) +1. (b) −1. (c) 0.
Q11. Name the only stable baryon.
- The proton.
- All other baryons eventually decay into protons.
Q12. What is associated production?
- When strange particles are produced in pairs via the strong interaction, conserving strangeness.
- For example, a K⁺ (S = +1) produced alongside a Λ⁰ (S = −1).