Retrieval Practice
Particles, Antiparticles & Photons — AQA A-Level Physics
Q1. State three properties that a particle and its antiparticle share, and one property that differs.
- Same: mass, rest mass-energy, magnitude of charge.
- Different: sign of charge (opposite).
Q2. Name the antiparticle of the electron.
The positron (e⁺).
Q3. Define a photon.
A massless discrete packet (quantum) of electromagnetic energy.
Q4. Write two equations for photon energy.
E = hf and E = hc/λ, where h = Planck's constant, f = frequency, c = speed of light, λ = wavelength.
Q5. Define annihilation and state the products.
When a particle meets its corresponding antiparticle, both are destroyed and their mass converts into two gamma-ray photons emitted in opposite directions.
Q6. What is the minimum energy of each photon produced in annihilation?
The rest mass-energy of one of the particles: E_min = E₀.
Q7. Define pair production and state the minimum photon energy required.
- When a photon interacts with a nucleus and its energy creates a particle-antiparticle pair.
- Minimum photon energy = 2E₀ (twice the rest mass-energy of one particle).
Q8. Name the four fundamental interactions in order of strength.
Strong nuclear (strongest), electromagnetic, weak nuclear, gravity (weakest).
Q9. State the exchange particle for each fundamental interaction.
- Strong: pion (between nucleons) or gluon (between quarks).
- Electromagnetic: virtual photon.
- Weak: W⁺, W⁻, Z⁰ bosons.
- Gravity: graviton (theorised).
Q10. Which exchange boson mediates (a) β⁻ decay and (b) β⁺ decay?
(a) W⁻ boson. (b) W⁺ boson.
Q11. Write the equation for electron capture.
- p + e⁻ → n + νₑ.
- Mediated by the W⁺ boson.
Q12. State three rules for drawing Feynman diagrams.
(1) y-axis = time, x-axis = space. (2) Particles = straight lines with arrows; exchange particles = wavy lines. (3) Charge, baryon number and lepton number conserved at each vertex.