AQA A-Level Physics Paper 1, June 2024: Question 17

1 mark · Medium difficulty · Multiple Choice

Identify which change increases the separation of fringes in a Young's double-slit interference experiment.

Practise this question

Question

Multiple choice question 17 asking how to increase the separation of fringes in a Young's double-slit experiment. Options are: A, using monochromatic light of lower frequency; B, decreasing the width of the single slit; C, increasing the separation of the double slits; D, decreasing the distance between the double slits and the screen.
Question text

17 Monochromatic light is used in a Young’s double-slit interference experiment after passing

through a single slit. The resulting fringe pattern is observed on a screen.

The separation of the fringes can be increased by

[1 mark]

A using monochromatic light of lower frequency.

B decreasing the width of the single slit.

C increasing the separation of the double slits.

D decreasing the distance between the double slits and the screen.

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 17 is option A, which is using monochromatic light of lower frequency, assessed under AO1.

17 A using monochromatic light of lower frequency. AO1

How to answer it

Young's Double-Slit Interference Fringe Separation

📌 What this question tests

This question assesses your understanding of wave optics, specifically the Young's double-slit equation ( w = λD / s ) and the relationships between fringe spacing ( w ), wavelength ( λ ), slit separation ( s ), distance to the screen ( D ), and wave properties like frequency ( f ) and wave speed ( c ).

Question 17 Analysis

Multiple Choice Question (1 Mark)

✅ Correct Answer: A

Using monochromatic light of lower frequency increases the wavelength ( λ = c / f ), which in turn increases the fringe separation ( w ).

💡 Key Knowledge

  • The fringe spacing formula is w = λD / s .
  • Wavelength and frequency are inversely proportional via c = fλ . Therefore, decreasing frequency ( f ) increases wavelength ( λ ).
  • A larger wavelength results in wider diffraction and interference effects, increasing fringe separation ( w ).

🧠 Exam Technique

  • Write down the relevant equation straight away in your exam margin: w = λD / s .
  • Break down multi-step relationships. If a variable like frequency ( f ) is given instead of wavelength ( λ ), recall the wave equation link immediately.

❌ Common Errors & Distractors

  • Option B: Altering the single slit width affects the overall envelope intensity/diffraction pattern, not the double-slit fringe separation ( w ).
  • Option C: Increasing slit separation ( s ) decreases fringe spacing ( w ) because they are inversely proportional.
  • Option D: Decreasing the distance to the screen ( D ) decreases fringe spacing ( w ).
Mark Scheme Allocation: 1 mark for selecting option A (AO1 - Demonstration of knowledge and understanding).

Topics

Physics · Practical skills · Required Practicals · 3.3 Waves · Data analysis · AS practicals (1–6)

Question and mark scheme from the AQA A-Level Physics examination, Paper 1, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.