AQA A-Level Physics Paper 1, June 2023: Question 13

1 mark · Medium difficulty · Multiple Choice

Identify which change produces a diffraction pattern with a larger radius from electrons passing through a crystalline sample.

Practise this question

Question

A multiple-choice question showing two circular diffraction patterns on fluorescent screens, where the rings in the second pattern are larger than the first. Options A through D list various experimental changes, and option A is correct.
Question text

13 Electrons with a certain kinetic energy pass through a powdered crystalline sample

and are incident on a fluorescent screen.

The diagram shows a sketch of the diffraction pattern produced.

A change is made and this second pattern is produced.

Which change could produce the second pattern?

[1 mark]

A decreasing the kinetic energy of the electrons

B replacing the electrons with protons with the same kinetic energy

C using a crystalline sample with a wider spacing between its atoms

D moving the screen closer to the crystalline sample

Mark scheme

Show the mark scheme The mark scheme shows that question 13 has the correct answer A, corresponding to 'decreasing the kinetic energy of the electrons'.

13 A decreasing the kinetic energy of the electrons

How to answer it

Electron Diffraction Pattern Analysis

Question 1.3 • Multiple Choice • [1 Mark]

What this question tests

This question assesses your understanding of wave-particle duality, specifically the de Broglie wavelength equation ( lambda = h / p or lambda = h / sqrt(2mE) ) and how changing physical parameters affects the ring spacing in a diffraction pattern produced by electrons passing through a powdered crystalline sample.

Exam Question Breakdown

✅ Correct Answer: A

Decreasing the kinetic energy of the electrons produces the second pattern, where the diffraction rings have expanded outward.

💡 Key Knowledge

  • de Broglie Wavelength: lambda = h / p . Since momentum p = sqrt(2mE) , a lower kinetic energy ( E ) results in a larger wavelength ( lambda ).
  • Diffraction Scaling: Larger wavelengths undergo greater diffraction (more spreading), causing the rings on the fluorescent screen to increase in diameter.

🧠 Exam Technique

Compare the visual patterns carefully. The rings in the second sketch are visibly larger in diameter than the first. Link ring size directly to scattering angle theta and Bragg's law / diffraction grating scaling ( sin(theta) is proportional to lambda ).

❌ Common Errors

  • Assuming protons with the same kinetic energy (Option B) would give the same pattern—forgetting that protons are much more massive than electrons, leading to a much smaller wavelength and tiny ring spacing.
  • Confusing inverse and direct relationships between kinetic energy and de Broglie wavelength.
Examiner Commentary: Top-level students quickly recognised that a larger diffraction pattern corresponds to a larger angle of diffraction, which requires a longer de Broglie wavelength. They immediately linked this to a decrease in electron velocity and kinetic energy.

Topics

Physics · 3.2 Particles and radiation

Question and mark scheme from the AQA A-Level Physics examination, Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.