A-level PHYSICS Paper 1 Please write clearly in block capitals. Centre number Candidate number Surname Forename(s) Candidate signature I declare this is my own work. 2 *02* IB/M/Jun24/7408/1 Do not write outside the Section A box Answer all questions in this section. 0 1 . 1 State the names of the four fundamental interactions. [1 mark] 1 2 3 4 0 1 . 2 State the products of the decay of a free neutron. [1 mark] 0 1 . 3 Explain which of the fundamental interactions is responsible for the decay of the neutron. [2 marks] 0 1 . 4 The forces between two moving electrons cause their paths to change. Explain, using the concept of exchange particles, why the electron paths change. [3 marks] 7 3 *03* Turn over ► IB/M/Jun24/7408/1 Do not write outside the 0 2 box A positive pion collides with a neutron and the following interaction is observed: + + 0 π →Κ + n + Σ Σ0 is a neutral sigma particle with a strangeness of −1 The interaction can be used to deduce the classifications of the Σ0 . 0 2 . 1 Identify the classifications of each particle in Table 1. Tick () the appropriate boxes for each particle. [2 marks] Table 1 Particle Baryon Hadron Lepton Meson π+ n K+ Σ0 0 2 . 2 A conservation rule predicts that the following interaction cannot occur: 0 + n + Σ − − π →Κ State the conservation rule. Go on to explain your answer. [3 marks] Question 2 continues on the next page 4 *04* IB/M/Jun24/7408/1 Do not write outside the One way in which neutral pions decay is box 0 + e + e + − π → γ 0 2 . 3 Compare the rest energies of the particles involved in this decay. [2 marks] 0 2 . 4 The decay of the neutral pion leads to the production of further gamma photons. Explain why. [1 mark] 0 2 . 5 The Standard Model is a theory that classifies elementary particles. Evidence for the theory has been collected since about 1950. However, the term Standard Model has only been used since 1973. Suggest why progress in particle physics is slow. [1 mark]