AQA AS Level Physics Paper 1, June 2019: Question 6

Mark scheme

Show the mark scheme

Question Answers Additional Comments/Guidance Mark

details

Particle with equal (rest) mass/energy

06.1 2 AO1.1a

but opposite charge/baryon number/lepton number

Antiproton

06.2 2 AO1.1a

Positron Do not accept antielectron for positron

0.510999 938.257 Allow valid use of E=mc2.

Rest energy of positron ( ) and antiproton ( )

quoted, or 938.768 (MeV) seen

06.3 Multiplies by 1.6 Allow any power of ten 3 AO2.1f

3.0 × 10–10 (J)

1.5 × 10–10 (J) Allow credit for for proton–

antiproton and electron–positron production

Max 3

Idea that (atomic) energy levels/states are discrete, or

(emitted) photon energy is discrete

06.4 Idea that a photon is produced by electrons/atoms moving to Allow light/radiation for “photon” 3 AO1.1a

lower energy levels/states

Idea that wavelength/frequency relates to photon energy/∆E May see equation relating ∆E to f or λ

Idea that different wavelengths/frequencies are produced

Total 10

How to answer it

Particles and Radiation: Antihydrogen Study Guide

What this question tests

This question assesses your knowledge of antimatter properties, naming conventions for antiparticles, performing rest energy calculations using unit conversions (MeV to Joules), and explaining the origin of line emission spectra using atomic energy levels.

Question 06.1 [2 marks]

State what is meant by an antiparticle.

✅ Correct Answer

Equal (rest) mass / energy to its corresponding particle (1 mark)
Opposite charge, baryon number, or lepton number (1 mark)

❌ Common Errors

Students often lose the second mark by stating it has an "opposite sign" without specifying a property, or incorrectly claiming antiparticles have negative mass.

Mark scheme guidance: Two independent marking points. Must mention equal mass/energy and opposite quantum numbers.

Question 06.2 [2 marks]

Complete Table 2 with the names of the antiparticles in an atom of antihydrogen.

✅ Correct Answers

Proton's antiparticle: Antiproton (1 mark)
Electron's antiparticle: Positron (1 mark)

❌ Common Errors

Writing "antielectron" is penalised by the examiners. You must use the accepted scientific term positron.

Mark scheme guidance: 1 mark per correct table entry. Strict rejection of 'antielectron'.

Question 06.3 [3 marks]

Calculate the total minimum energy, in J, needed to produce the particles in one atom of antihydrogen.

📐 Step-by-Step Calculation

Find rest energies: Quote or look up rest energy values from your data booklet:
Positron = 0.510999 MeV
Antiproton = 938.257 MeV (or 938.768 MeV total combined)
Sum the energies:
0.511 MeV + 938.257 MeV = 938.768 MeV
Convert MeV to Joules: Multiply by 1.6 × 10⁻¹³ J MeV⁻¹
938.768 × 1.6 × 10⁻¹³ = 1.50 × 10⁻¹⁰ J

🧠 Exam Technique & Traps

Minimum energy: Pair production requires energy equal to the rest mass energy of the particle-antiparticle pairs created.
Unit conversion trap: Forgetting to convert from MeV to Joules is the most common place students drop marks.

Mark scheme guidance: 1 mark for quoting rest energies, 1 mark for multiplying by the eV conversion factor (1.6 × 10⁻¹³), 1 mark for final answer (~1.5 × 10⁻¹⁰ J).

Question 06.4 [3 marks]

Explain in terms of energy changes how line emission spectra are produced.

💡 Key Knowledge (Max 3 Marks)

Atomic energy levels / states are discrete (quantised).
Photons are emitted when electrons/atoms transition from a higher to a lower energy level.
The energy of the emitted photon is equal to the difference in energy between the two levels ( ΔE = hf ), resulting in specific, discrete wavelengths or frequencies.

🧠 Top-Level Responses

To secure full marks, explicitly link the discrete nature of energy levels to the discrete frequencies/wavelengths observed in the emission spectrum. Use precise terminology like transition, discrete, and photon energy.

Mark scheme guidance: Max 3 marks awarded from the pool of valid physics points. Clear logical flow is essential.

Topics

Physics · 3.2 Particles and radiation