OxfordAQA International AS and A-level Physics: Atomic structure and elementary particles (9630) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover sections 3.3.1 and 3.3.2 of the OxfordAQA International AS and A-level Physics (9630) specification, Version 4.4. The content is shared International AS and A-level. Use these data where a question needs them: proton charge 1.60 × 10⁻¹⁹ C; proton and neutron mass 1.67 × 10⁻²⁷ kg each; electron mass 9.11 × 10⁻³¹ kg; 1 MeV = 1.60 × 10⁻¹³ J; electron rest energy 0.511 MeV; proton rest energy 938.3 MeV.

Read the study guide first if needed, and use the revision notes for recall. Course pages: physics hub and checklist.

Questions

1. A neutral atom of copper has proton number 29 and nucleon number 63. Give the proton, neutron and electron counts for a copper ion of charge +2e with the same nucleus. [3]

2. The nucleus of phosphorus-31 has proton number 15. Calculate its specific charge and compare it with that of the proton. [4]

3. Describe the Rutherford alpha-particle scattering experiment and explain what its results show about the atom. [6]

4. Explain how the results of the scattering experiment led physicists to drop the model with positive charge smeared across the whole atom. [4]

5.

(a) Calculate the mass of an electron as a fraction of the mass of a proton. [2] (b) Explain why the specific charge of an electron is about 1800 times that of a proton. [2]

6.

(a) Name the antiparticles of the electron and of the neutrino. [2] (b) State the charge and the rest energy, in MeV, of an antiproton. [2]

7. An electron and a positron, each with kinetic energy 1.20 MeV, collide head-on and annihilate to produce two photons.

(a) Calculate the energy of each photon in MeV. [3] (b) Give the photon energy in joules. [1] (c) Explain why two photons are produced rather than one. [1]

8. A photon of energy 2.00 MeV passes close to a nucleus and produces an electron-positron pair.

(a) Calculate the total kinetic energy of the pair and, if shared equally, of each particle. [3] (b) State why the same photon could not produce a proton-antiproton pair. [1] (c) State the net charge of the pair and why this is consistent with the photon. [1]

9. A neutron and an antineutron at rest annihilate to form two photons. The neutron rest energy is 939.6 MeV.

(a) Calculate the total energy released, in MeV, and the energy of each photon. [3] (b) Convert the energy of one photon to joules. [1] (c) The Planck constant is 6.63 × 10⁻³⁴ J s. Calculate the frequency of one photon. [2] (d) State the minimum energy of a photon able to produce a neutron-antineutron pair. [1]

10. In a scattering investigation, 30 000 alpha particles were counted at different angles.

Deflection angle	Particles counted
0° to 5°	29 120
5° to 30°	810
30° to 90°	65
Above 90°	5

(a) Calculate the fraction deflected through more than 90°, and write it as “1 in N”. [2] (b) State what the counts at the smallest angles show about the atom. [2] (c) Explain what the particles deflected above 90° show about the nucleus. [2] (d) Predict how many of a further 12 000 alpha particles would exceed 90°, and explain why the count may differ. [2]

11. A chloride ion has proton number 17, nucleon number 35 and charge −e.

(a) State its numbers of protons, neutrons and electrons. [3] (b) Calculate its specific charge, including the mass of the electrons. [3] (c) Calculate the specific charge of the ion with nucleon number 37 and the same charge, and explain why it differs. [2]

12. A helium-4 nucleus (charge +2e) and a hydrogen-2 nucleus (charge +e) have equal specific charges.

(a) Show that the hydrogen-2 nucleus has specific charge 4.79 × 10⁷ C kg⁻¹. [2] (b) Explain why the two values are equal. [1] (c) State two other properties that distinguish the two nuclei, with values. [2]

Answers

1. Protons = 29 [1]. Neutrons = 63 − 29 = 34 [1]. Electrons = 29 − 2 = 27 [1]. [3] Examiner insight: Answers usually earn credit for showing the subtraction A − Z and the electron count adjusted for the ion charge, not the neutral atom.

2. Charge = 15 × 1.60 × 10⁻¹⁹ = 2.40 × 10⁻¹⁸ C [1]. Mass = 31 × 1.67 × 10⁻²⁷ = 5.18 × 10⁻²⁶ kg [1]. Specific charge = 2.40 × 10⁻¹⁸ ÷ 5.18 × 10⁻²⁶ = 4.64 × 10⁷ C kg⁻¹ [1]. The proton’s is 9.58 × 10⁷ C kg⁻¹, so the nucleus’s value is slightly less than half of it [1]. [4] Examiner insight: A compare question needs a stated relationship, such as “half”, backed by both numbers, and units must be on the final value.

3. A beam of alpha particles from a source is aimed at a thin gold foil [1], in a vacuum so air does not absorb or scatter them [1], with a movable detector counting particles at different angles [1]. Most went straight on with little deflection, which shows the atom is largely empty [1]. A few were deflected through large angles, so a small region of positive charge repels the alpha particles [1]. A very few rebounded, so that region, the nucleus, is also very massive [1]. [6] Examiner insight: Write each observation next to the conclusion it supports; a block of observations followed by a block of conclusions tends to lose that link.

4. The earlier model had positive charge spread through the atom with electrons embedded [1]. That model predicts only small deflections of alpha particles [1]. The observation of large-angle deflections and some rebounds contradicted it [1]. A small, dense, positive nucleus explained the results, so the nuclear model replaced it [1]. [4] Examiner insight: Strong answers state what the old model predicted before saying what was observed, because “contradicted” needs both sides.

5. (a) 9.11 × 10⁻³¹ ÷ 1.67 × 10⁻²⁷ [1] = 5.45 × 10⁻⁴ [1] (b) The charges have equal magnitude [1]. The electron mass is about 1/1800 of the proton mass, so charge ÷ mass is about 1800 times larger [1]. [4] Examiner insight: For an explain question, say which quantity is equal and which is different; “because it is lighter” alone is incomplete.

6. (a) Positron [1] and antineutrino [1]. (b) Charge −1.60 × 10⁻¹⁹ C, relative charge −1 [1]. Rest energy 938.3 MeV, the same as the proton [1]. [4] Examiner insight: Giving the charge as a sign only is risky; give it in coulombs or as a relative charge.

7. (a) Each particle has 0.511 + 1.20 = 1.711 MeV [1]. Total = 3.422 MeV [1]. Equal and opposite photons: 1.71 MeV each [1]. (b) 1.711 × 1.60 × 10⁻¹³ = 2.74 × 10⁻¹³ J [1] (c) Momentum must be conserved, and a single photon would leave non-zero total momentum [1]. [5] Examiner insight: A common slip is using only the kinetic energy or only the rest energy; show both added before you halve.

8. (a) Energy for the pair’s rest energy = 2 × 0.511 = 1.022 MeV [1]. Kinetic energy = 2.00 − 1.022 = 0.978 MeV [1]. Each: 0.489 MeV [1]. (b) A proton-antiproton pair needs at least 1876.6 MeV, far above 2.00 MeV [1]. (c) The pair has zero net charge, the same as the photon, so charge is conserved [1]. [5] Examiner insight: “Not enough energy” is a stronger answer when it is compared with a stated threshold value.

9. (a) Total = 2 × 939.6 = 1879.2 MeV [1]. Each photon = 939.6 MeV [1], because the particles are at rest and the photons have equal energy [1]. (b) 939.6 × 1.60 × 10⁻¹³ = 1.50 × 10⁻¹⁰ J [1] (c) f = E ÷ h = 1.50 × 10⁻¹⁰ ÷ 6.63 × 10⁻³⁴ [1] = 2.27 × 10²³ Hz [1] (d) 1879.2 MeV [1] [7] Examiner insight: Convert MeV to joules before using E = hf; mixing MeV with the Planck constant in joule seconds gives an answer wrong by a factor of 10¹³.

10. (a) 5 ÷ 30 000 = 1.67 × 10⁻⁴ [1], which is 1 in 6000 [1]. (b) Nearly all particles (29 120 out of 30 000) were barely deflected [1], so most of the atom is empty space [1]. (c) Large deflection needs a strong repulsive force from a concentrated positive charge [1]. Rebounds need the target to be massive, so the nucleus is small, dense and positive [1]. (d) 12 000 × 5 ÷ 30 000 = 2 [1]. Scattering is random, so a small count varies from run to run [1]. [8] Examiner insight: Quote figures from the table when you interpret data, and note that tiny counts are subject to chance.

11. (a) Protons 17, neutrons 35 − 17 = 18, electrons 17 + 1 = 18 [1] [1] [1]. (b) Charge = −1.60 × 10⁻¹⁹ C [1]. Mass = 35 × 1.67 × 10⁻²⁷ + 18 × 9.11 × 10⁻³¹ = 5.85 × 10⁻²⁶ kg [1]. Specific charge = −2.74 × 10⁶ C kg⁻¹ [1]. (c) 1.60 × 10⁻¹⁹ ÷ (37 × 1.67 × 10⁻²⁷) = 2.59 × 10⁶ C kg⁻¹ (magnitude) [1]. Same charge but two extra neutrons give a larger mass [1]. [8] Examiner insight: Keeping the negative sign and showing that electron mass barely changes the value both help; a bare unsigned number loses the sign.

12. (a) Specific charge = 1.60 × 10⁻¹⁹ ÷ (2 × 1.67 × 10⁻²⁷) [1] = 4.79 × 10⁷ C kg⁻¹ [1]. (b) Each has a charge-to-nucleon ratio of 1 : 2, so charge ÷ mass is the same [1]. (c) Charge differs: +3.20 × 10⁻¹⁹ C for helium-4 and +1.60 × 10⁻¹⁹ C for hydrogen-2 [1]. Mass differs: 6.68 × 10⁻²⁷ kg and 3.34 × 10⁻²⁷ kg [1]. [5] Examiner insight: A “show that” needs the unrounded working followed by the stated value; here that is the division line then 4.79 × 10⁷.

Where marks are usually lost

• Using A as the neutron count instead of A − Z.
• Ignoring the sign of the specific charge for negative ions and electrons.
• Using Z protons for an ion’s charge instead of the net charge.
• Listing Rutherford observations without linking each to its conclusion.
• Writing “attraction” when the alpha particle is repelled by the nucleus.
• Using a single rest energy as the pair-production threshold.
• Leaving energies in MeV when joules are requested, or using MeV with the Planck constant.
• Giving a vague “not enough energy” with no threshold figure.

Next steps

• Recall notes: revision notes
• Full explanations: study guide
• Course pages: physics hub and checklist
• Find your gaps: all free 10-minute diagnostics
• Book a free trial class

Official syllabus

OxfordAQA International AS and A-level Physics (9630), sections 3.3.1 and 3.3.2, Version 4.4 (for exams May/June 2020 onwards), published by OxfordAQA.