AQA A-Level Physics Paper 1, June 2024: Question 16

1 mark · Medium difficulty · Multiple Choice

Identify the expression representing the wavelength of sound from two coherent point sources producing interference maxima at W and Y.

Practise this question

Question

A diagram shows two point sources of sound S1 and S2 on the left, and a line PQ on the right with four marked points W, X, Y, and Z. Text asks for the wavelength of sound given that consecutive maxima of sound intensity are detected at W and Y and consecutive minima at X and Z, followed by four multiple-choice options A, B, C, and D involving path differences.
Question text

16 Point sources of sound of the same frequency are placed at S1 and S2.

A sound detector is moved slowly along the line PQ. Consecutive maxima of sound

intensity are detected at W and Y and consecutive minima are detected at X and Z.

What is the wavelength of the sound?

[1 mark]

A (S1Y−S2Y) − (S1W−S2W)

B (S1X−S2X) − (S1W−S2W)

C (S1Y−S2Y) − (S1X−S2X)

D (S1Z−S2Z) − (S1W−S2W)

Mark scheme

Show the mark scheme A table showing that the correct answer for question 16 is A, with the expression (S1Y - S2Y) - (S1W - S2W) categorized under AO1.

16 A (S1Y−S2Y) − (S1W−S2W) AO1

How to answer it

Interference and Path Difference of Sound Waves

What this question tests: Understanding of wave superposition, constructive interference (maxima), path difference relationships, and how the wavelength of a wave relates to the separation between consecutive maxima from two coherent point sources.
Question 16

Multiple Choice Analysis

✅ Correct Answer: A

(S₁Y − S₂Y) − (S₁W − S₂W)

Consecutive maxima occur at points where the path difference increases by exactly one wavelength (λ).

💡 Key Knowledge

  • Constructive Interference: Path difference = nλ (where n is an integer).
  • Consecutive Maxima: The path difference changes from nλ to (n + 1)λ.
  • Wavelength Equation: Subtracting the path difference at maximum W from maximum Y yields exactly one wavelength (λ).

🧠 Exam Technique

  • Identify the points mentioned in the question: W and Y are consecutive maxima.
  • Write down the path difference formula for each point: S₁W − S₂W and S₁Y − S₂Y .
  • Since they are consecutive, the difference between their path differences must equal one wavelength (λ).

❌ Common Errors

  • Confusing maxima with minima (using points X and Z which are minima).
  • Mixing up addition and subtraction when finding the change in path difference between two points.
Mark Allocation: [1 mark] for selecting option A.

Topics

Physics · 3.3 Waves

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.