AQA A-Level Physics Paper 1, June 2023: Question 17

1 mark · Medium difficulty · Multiple Choice

Determine the effect of increasing the slit width on the width and brightness of the central maximum in a single-slit diffraction pattern.

Practise this question

Question

A multiple-choice question numbered 17. It asks what happens to the width and brightness of the central maximum of a single-slit diffraction pattern when the slit width is increased. A table with options A to D gives combinations of 'increases' or 'decreases' for both the width and brightness of the central maximum.
Question text

17 A single narrow slit is illuminated with monochromatic light and a diffraction pattern

is produced.

The slit width is increased.

What happens to the width and brightness of the central maximum of the diffraction

pattern?

[1 mark]

Width of central maximum Brightness of central maximum

A increases increases

B increases decreases

C decreases increases

D decreases decreases

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 17 is option C, where the width of the central maximum decreases and the brightness increases.

17 C decreases increases

How to answer it

Single Slit Diffraction Patterns

Question 17 • 1 Mark

What this question tests

This question assesses your understanding of wave optics, specifically how changing the physical dimensions of a single slit affects both the angular width (or linear width) and the intensity/brightness of the central maximum in a diffraction pattern.

Question Part 17

Effect of Increasing Slit Width on the Central Maximum

✅ Correct Answer

Option C: Width of central maximum decreases, Brightness of central maximum increases.

💡 Key Knowledge

  • Width relationship: The angular width of the central maximum is given by w = 2λ / a (where a is slit width). Therefore, width is inversely proportional to a . A larger slit width means less diffraction (narrower pattern).
  • Brightness relationship: When the slit is widened, more light passes through the slit onto the screen overall. Because this greater amount of light energy is concentrated into a smaller area (narrower central maximum), the central fringe becomes brighter.

🧠 Exam Technique

Split multi-variable multiple-choice questions into steps. First, evaluate how one variable changes using your formula sheet equations ( w ∝ 1/a ). Once you narrow down the options to two choices, use conservation of energy/intensity reasoning to determine the brightness change.

❌ Common Errors

Students often confuse single-slit diffraction equations with double-slit interference fringe spacing formulas ( w = λD / s ), or incorrectly assume that spreading light out over a wider area makes it brighter rather than dimmer.

Mark Scheme Note: 1 mark awarded for selecting option C.

Topics

Physics · 3.3 Waves

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.