Particles and the standard model: Edexcel International A Level Physics questions

Every Edexcel International A Level Physics exam question on Particles and the standard model (specification points 118–124), 2019–2025, with its mark scheme and examiner’s report.

All 97 questions on Particles and the standard model, as a list

June 2025, Unit 4, Q4 (1 mark): In the upper atmosphere, high‑energy cosmic rays collide with molecules of air to produce muons. The average speed of these muons is v. The average lifetime of
June 2025, Unit 4, Q7 (1 mark): An electron and a positron collide and annihilate, producing two photons. Which of the following is the energy, in joules, of one of these photons? A 9.11 × 10
June 2025, Unit 4, Q14(a)(i) (1 mark): State the quark structure of a meson. (1)
June 2025, Unit 4, Q14(a)(ii) (2 marks): Explain how the law of conservation of baryon number and the law of conservation of charge are obeyed in this reaction. (2)
June 2025, Unit 4, Q14(b) (3 marks): Before its discovery, the mass of the Ω – was predicted to be 2.9714 × 10 –27 kg. The most recent accepted value for the mass of the Ω – is 1672 MeV/c 2. Calcul
June 2025, Unit 4, Q14(c) (3 marks): The photograph shows tracks produced by particles in a particle detector when a K – collided with a stationary proton. The tracks produced by the K + and Ω – ar
January 2025, Unit 4, Q2 (1 mark): The standard quark‑lepton model includes particles called mesons. Which of the following is a meson? A photon B pion C positron D proton
January 2025, Unit 4, Q4 (1 mark): The positron is the antiparticle of the electron. Which row of the table gives a similarity and a difference between a positron and an electron? Similarity Diff
January 2025, Unit 4, Q7 (1 mark): In pair production, a high energy photon creates a particle‑antiparticle pair. In one interaction, a photon produces an electron and a positron. Which of the fo
January 2025, Unit 4, Q11 (3 marks): A nuclear reaction that occurs in the Sun is shown. p + p → p + n + e + + ve Two protons react to form a proton, a neutron, a positron, and an electron neutrino
October 2024, Unit 4, Q3 (1 mark): Which row of the table shows a fundamental particle and a non-fundamental particle? Fundamental Non-fundamental A alpha neutron B lepton meson C proton electron
October 2024, Unit 4, Q10 (1 mark): A proton and an anti-proton travel in opposite directions towards each other. Each particle has energy of 450 GeV. When the particles collide, they annihilate a
October 2024, Unit 4, Q13(a) (2 marks): A muon is travelling at 98.0% of the speed of light. Show that the distance travelled by the muon in 2.20 μs is about 650 m. (2)
October 2024, Unit 4, Q13(b) (3 marks): Some muons are produced 15 000 m above the ground and travel vertically downwards. Explain why most of these muons reach the ground before decaying. (3)
October 2024, Unit 4, Q18(b)(i) (1 mark): The Σ + particle is made of two up quarks and one strange quark. State what type of particle Σ + is. (1)
October 2024, Unit 4, Q18(b)(ii) (4 marks): Deduce whether the conservation of charge and the conservation of lepton number apply to this decay. (4)
June 2024, Unit 4, Q11(b) (2 marks): A book about the Chadwick experiment includes the following statement: “Chadwick’s experiment established that the neutron was a new fundamental particle and no
June 2024, Unit 4, Q14(a) (2 marks): State the quark structure of baryons and of mesons. (2) Baryon Meson
June 2024, Unit 4, Q14(b)(i) (5 marks): One type of leptoquark has charge +5e/3 Determine the baryon number and the lepton number for this leptoquark. Include the suggested quark and lepton in your wo
June 2024, Unit 4, Q14(b)(ii) (3 marks): Scientists search for new particles using high energy particle collisions. The highest energy particle collisions involve colliding protons moving in opposite d
June 2024, Unit 4, Q14(b)(iii) (1 mark): Leptoquarks have not yet been observed. Suggest why leptoquarks have not yet been observed. (1)
June 2024, Unit 4, Q16(a) (3 marks): The high energy electrons produced will have energy 60 GeV. Show that these electrons will be travelling at relativistic speeds. (3)
January 2024, Unit 4, Q6 (1 mark): A pion can decay into two leptons. Which of the following decays is possible? A π – → e – + ve B π 0 → e – + ve C π 0 → e + + ve D π + → e + + ve
January 2024, Unit 4, Q12 (3 marks): The diagram shows tracks produced by particles in a bubble chamber. P A charged particle interacts with a stationary proton at P. This produces two neutral part
January 2024, Unit 4, Q22(a)(i) (2 marks): The following table lists some quarks and their charge. Quark Charge / e + 2 Up (u) 3 − 1 Down (d) 3 − 1 Strange (s) 3 Explain the quark structure of a K – meso
January 2024, Unit 4, Q22(a)(ii) (3 marks): The mass of a K – meson is 494 MeV / c 2. Calculate the mass of a K – meson in kg. (3) – meson mass = kg K
October 2023, Unit 4, Q6 (1 mark): A particle detector shows tracks produced by two particles X and Y. The particles were created by the decay of a kaon at O. X Y O Which of the following can be
October 2023, Unit 4, Q21(a) (1 mark): Give a possible quark structure of a pion. (1)
October 2023, Unit 4, Q21(b) (4 marks): The equation shows a pion decaying into a muon and an antineutrino. π– → μ– + νμ– Energy and momentum must be conserved in this decay. Explain two other conserv
October 2023, Unit 4, Q21(c) (3 marks): Calculate the mass, in kg, of a muon. (3) Mass of muon = kg
October 2023, Unit 4, Q21(d) (2 marks): When at rest, pions have an average lifetime of 26 ns. When produced in the upper atmosphere, high-energy pions have a speed of up to 0.99 c. Explain how the av
June 2023, Unit 4, Q6 (1 mark): Which of the following is a fundamental particle? A neutrino B neutron C pion D proton
June 2023, Unit 4, Q7 (1 mark): A particle has mass 6.5 MeV / c 2. Which of the following gives the mass, in kg, of the particle? 19 6 5 . 1 6 . 10 A 2 8 3 10 13 6 5 . 1 6 . 10 B 2 8 3 10 2 C
June 2023, Unit 4, Q9 (1 mark): Which of the following shows the β – decay of a nucleon? A n → p + β – + νe B n → p + β – + νe C p → n + β – + νe D p → n + β – + νe
June 2023, Unit 4, Q11 (5 marks): In 2022, CERN announced the discovery of a new particle known as a pentaquark which is made of five quarks. The table shows the charges on some quarks. Quark Ch
January 2023, Unit 4, Q1 (1 mark): The table shows the charges on up quarks and down quarks. Quark Charge / e + 2 u 3 – 1 d 3 Which row of the table shows the quark structure of protons and neutr
January 2023, Unit 4, Q11(a) (1 mark): State one difference between a positron and an electron. (1)
January 2023, Unit 4, Q11(b) (3 marks): Explain whether the following decay would be possible. You should consider conservation of charge and lepton number. – → e – + νe + ν – μ μ (3)
January 2023, Unit 4, Q18(a)(i) (3 marks): Explain why the existence of a sixth quark was predicted. (3)
January 2023, Unit 4, Q18(a)(ii) (1 mark): A short time after formation, most quarks combine to make particles known as hadrons. There are two categories of hadron. Name the two categories of hadron. (1)
January 2023, Unit 4, Q18(b)(ii) (3 marks): In the collider experiment, the protons and anti-protons each had total energy 900 GeV. Calculate the maximum kinetic energy, in joules, of a top quark produced
January 2023, Unit 4, Q18(b)(iii) (3 marks): Deduce whether a top quark with kinetic energy 1.2 × 10 relativistic speed. 2 rest mass of top quark = 173 GeV/c (3)
January 2023, Unit 4, Q18(c) (2 marks): Most types of quark form hadrons on a timescale of 10 −25 s. form hadrons because its lifetime is only 10 A student suggests that, if the top quarks travelled a
January 2023, Unit 5, Q16(b) (3 marks): The theory suggests that the mass of the new type of neutrino particle is 4.8 × 10 8 GeV/c 2. Calculate the mass of this particle in kg. (3) Mass of particle =
October 2022, Unit 4, Q1 (1 mark): Which row of the table describes the mass and charge of an anti-proton? Mass / kg Charge / C A −27 −19 1.67 × 10 1.6 × 10 B −27 −19 1.67 × 10 −1.6 × 10 C −27 −1
October 2022, Unit 4, Q7 (1 mark): The table shows the relative charges on up and down quarks. 2 u 3 e − 1 3 e d Which of the following could be the quark composition for a baryon with a charge o
October 2022, Unit 4, Q11(a) (1 mark): Pions belong to a group of particles known as mesons. State the quark structure of mesons. (1)
October 2022, Unit 4, Q11(b) (1 mark): Muons belong to a family of particles known as leptons. State one property of leptons. (1)
October 2022, Unit 4, Q11(c) (4 marks): Charged pions usually decay into a muon (μ) and another particle X, as shown by the decay equation: π – → μ – + X A student suggests that X is an anti-neutrino
October 2022, Unit 4, Q13(a) (4 marks): The mass of the Z boson is 91 GeV/c 2. Show that the mass of the Z boson is nearly 100 times greater than the mass of a proton. (4)
October 2022, Unit 4, Q13(b) (3 marks): Protons and anti-protons were accelerated in the Spp–S to very high energies before they collided. Explain why the protons and anti-protons needed high energies
October 2022, Unit 4, Q13(c) (2 marks): Z bosons produced by high energy collisions can have a range of lifetimes. The Z bosons with the longest lifetimes are those that were moving very fast. Explain
October 2022, Unit 5, Q18(b) (4 marks): Radioactive phosphorus was one of the first artificially produced isotopes to be used in the diagnosis of cancerous tumours. The isotope 32P is injected into a
June 2022, Unit 4, Q1 (1 mark): Which of the following is a fundamental particle? A pion B proton C neutrino D neutron
June 2022, Unit 4, Q2 (1 mark): A proton collides with an antiproton. Which of the following could be produced by this collision? A π + + n B π − + p+ C π + + e− D π + + π −
June 2022, Unit 4, Q7 (1 mark): Muons can travel at speeds close to the speed of light. At these speeds the lifetime and mass of a muon are different from those of a stationary muon. Which row
June 2022, Unit 4, Q14(b) (2 marks): State two ways that the diagram shows the kaon is neutral. (2)
June 2022, Unit 4, Q14(c) (2 marks): The table shows the charge for the up quark and the down quark as a fraction of the charge on the proton. Quark Charge u +2/3 d –1/3 Deduce the quark structure
June 2022, Unit 4, Q14(d) (3 marks): Calculate the mass of a proton in GeV/c2. (3) Mass = GeV/c2
June 2022, Unit 5, Q13(b) (2 marks): Occasionally 40K decays by emitting a β+ particle. Give two similarities between a β– particle and a β+ particle. (2)
January 2022, Unit 4, Q2 (1 mark): Which row in the table gives the charge and mass of an antiproton? Charge / C Mass / kg A 1.6 × 10−19 −9.11 × 10−31 B −1.6 × 10−19 9.11 × 10−31 C 1.6 × 10−19 −1
January 2022, Unit 4, Q16(b)(i) (2 marks): Describe the structure of a baryon and a meson. (2)
January 2022, Unit 4, Q16(b)(iii) (3 marks): Deduce the charge and baryon number for the omega particle. (3)
January 2022, Unit 4, Q16(c) (6 marks): The rest mass of the omega baryon is significantly larger than the rest mass of the proton. Discuss how energy and momentum are conserved during this collision.
January 2022, Unit 4, Q17(a) (2 marks): The muon belongs to the same family of particles as the electron. State how the muon is classified in the standard model. (2)
January 2022, Unit 4, Q17(b) (2 marks): A muon (μ) can be produced by the decay shown in this nuclear equation. π− → μ− + ν− μ State the names of the two other particles involved. (2)
January 2022, Unit 4, Q17(c) (3 marks): A website states: “The rest mass of a muon is 106 MeV / c2, which is a little over 200 times that of an electron.” Deduce whether this statement is correct. (3)
January 2022, Unit 4, Q17(d)(i) (2 marks): Explain why the unit GeV / c is a valid unit for momentum. (2)
January 2022, Unit 4, Q17(d)(ii) (3 marks): Deduce whether the website’s claim is correct. muon charge = −1.6 × 10−19 C 3.10 GeV/c = 1.65 × 10–18 N s (3)
January 2022, Unit 4, Q17(d)(iii) (2 marks): Stationary muons are unstable and have a mean lifetime of a few microseconds. Explain why muons in the ring are observed to have a much greater mean lifetime. (
October 2021, Unit 4, Q1 (1 mark): Which of the following is a fundamental particle? A atom B baryon C neutrino D pion
October 2021, Unit 4, Q9 (1 mark): Which of the following is the quark structure for a π– particle? A d d d B u u d C u d D u d
October 2021, Unit 4, Q16(c) (3 marks): Most of the particles detected in the spark chamber are muons. The muons were created in the upper atmosphere. Muons normally have a very short lifetime and sho
October 2021, Unit 4, Q17(b)(i) (4 marks): An omega baryon has a mass equivalent to 3272 times the mass of an electron. Show that the mass of an omega baryon is about 1700 MeV/c2. (4)
October 2021, Unit 4, Q17(b)(ii) (3 marks): Calculate the kinetic energy of one of the omega baryons. (3) Kinetic energy =
October 2021, Unit 4, Q17(c) (3 marks): A student correctly suggests that this collision cannot lead to both particles being omega baryons, as this breaks a conservation law. Discuss the student’s sug
October 2021, Unit 4, Q18(a) (2 marks): State two ways in which the diagram shows that an anti‑muon must also have a positive charge. (2)
October 2021, Unit 4, Q18(e)(i) (1 mark): Write an equation for this decay process. (1)
June 2021, Unit 4, Q1 (1 mark): Which of the following is a fundamental particle? A antiproton B muon C neutron D pion
June 2021, Unit 4, Q3 (1 mark): Neutrinos can interact with protons to create neutrons. Which of the following equations shows this process? A νe + p → e+ + n B νe + p → e– + n C ν– e + p → e+
June 2021, Unit 4, Q4 (1 mark): In 2015, a pentaquark was discovered. The pentaquark was made of 5 quarks, c, c–, d, u, u. The pentaquark can form a baryon-meson combination. Which row of the
June 2021, Unit 4, Q18(a) (3 marks): State the properties of a positron that show it is the antiparticle to the electron. (3)
June 2021, Unit 4, Q18(c)(i) (3 marks): Show that the positron must have been travelling at a relativistic speed. Assume that all of its energy is kinetic energy. (3)
June 2021, Unit 4, Q18(d) (4 marks): A positron travelling at a non-relativistic speed of 1.5 × 107 m s−1 collides with an electron travelling at the same speed in the opposite direction. This coll
January 2021, Unit 4, Q4 (1 mark): A particle has a mass of 3.17 × 10−27 kg. Which of the following gives the mass in GeV/c2? 3 17 . × 10 × 10 × 1 6 . × 10 − 27 9 − 19 A 3 00 . × 10 8 3 17 . × 10
January 2021, Unit 4, Q13(a) (2 marks): Explain how energy is conserved in this decay. (2)
January 2021, Unit 4, Q13(b) (6 marks): The equation shows the decay of an anti-neutron. 1 n¯ → −1 1 p¯ + 1 0 e¯ + νe 0 Explain how this equation shows that the decay obeys three conservation laws. (6
January 2021, Unit 4, Q14(a) (5 marks): Explain whether these observations are consistent with ideas from relativity. Your answer should include a calculation. (5)
January 2021, Unit 4, Q14(b) (2 marks): After muons were discovered in 1936 they were known for many years as mu mesons. Explain why muons are not described as mesons in the standard model. (2)
October 2020, Unit 4, Q2 (1 mark): A student writes the following equation for the decay of a neutron. n → p + e– + νe Which of the following conservation laws is violated by the equation he has
October 2020, Unit 4, Q12(a) (1 mark): Name the process involved in producing the gamma photons. (1)
October 2020, Unit 4, Q12(b) (4 marks): Calculate the maximum wavelength of the gamma photons produced. (4) Wavelength =
October 2020, Unit 4, Q13 (4 marks): In 1964 George Zweig proposed a model for matter. Zweig suggested that mesons and baryons are made from a set of fundamental particles he called aces. In this m
October 2020, Unit 5, Q18(b)(ii) (5 marks): It is claimed that calcium ions with an energy of 245 MeV are travelling at relativistic speeds. Assess the validity of this claim. mass of calcium ion = 47.95
January 2020, Unit 4, Q1 (1 mark): A neutron can decay to produce a proton. Which of the following equations correctly shows neutron decay? A n o p + e+ + ve B n o p + e+ + ve C n o p + e– + ve D
January 2020, Unit 4, Q6 (1 mark): A gamma photon of energy 18 MeV produces a particle and its antiparticle. Which of the following will give the maximum possible mass of the particle in kg? − 19
January 2020, Unit 4, Q12 (6 marks): The following passage is taken from an article about the history of particle physics. Mystery Particle By 1932 scientists knew of the existence of the subatomic

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