Conservation laws and particle equationsEdexcel A-Level Physics: Flashcards
What these 13 flashcards ask
- Which three quantities do you check to decide if an interaction is possible?
- What is the baryon number of a proton, of a meson and of an antiproton?
- What is the lepton number of an electron, a positron and an electron antineutrino?
- Write the equation for β⁻ decay of a neutron.
- Write the equation for β⁺ decay of a proton.
- Write the equation for electron capture by a proton.
- Why must an antineutrino be emitted in β⁻ decay?
- Why is p → e⁺ + π⁰ impossible?
- What are the lepton number and baryon number of a photon?
- Write the decay of the positive pion into a muon.
- In n + νe → p + X, what is X?
- What changes in a nucleus in β⁺ decay?
- If a process conserves charge and baryon number but not lepton number, is it possible?
Exam questions on Conservation laws and particle equations
- In β⁻ decay a neutron in an unstable nucleus changes into a proton, and an electron and a third particle X are emitted. The neutron and proton are baryons with baryon number +1, and the neutron, proton and electron have lepton numbers 0, 0 and +1 respectively.Write the particle equation for the decay and show that charge and lepton number are conserved.2 marks
- A positive pion (π⁺) decays into a positive muon and a muon neutrino, π⁺ → μ⁺ + νμ. The pion is a meson with baryon number 0 and lepton number 0. Muons and neutrinos are leptons with lepton number +1, and their antiparticles have lepton number −1.The positive muon decays as μ⁺ → e⁺ + νe + ν̄μ. Show that charge and lepton number are conserved in this decay.2 marks
- Particle physicists analyse the products of high-energy collisions between protons. Pions are mesons with baryon number 0 and lepton number 0; the π⁺, π⁻ and π⁰ have charges +1 e, −1 e and 0. An antiproton has charge −1 e and baryon number −1.In one collision, p + p → p + n + X, where X is a single particle. Use conservation laws to identify X.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).