AQA A-Level Physics Paper 1, June 2024: Question 14

1 mark · Medium difficulty · Multiple Choice

Identify whether light waves from two different sources are unpolarised or polarised based on the change in detected intensity when a rotating polaroid filter is introduced.

Practise this question

Question

Multiple choice question 14 asks to identify whether light waves from source S1 and source S2 are unpolarised or polarised. The table provides four options (A, B, C, D) with combinations of unpolarised and polarised for S1 and S2 respectively. The scenario describes rotating a polaroid material placed between the sources and a detector: the intensity from S1 does not change when rotated, while the intensity from S2 decreases.
Question text

14 A detector measures the intensity of light from a source S1.

Polaroid material is placed between source S1 and the detector. When the material is

rotated through a small angle, the detected intensity does not change.

When this procedure is repeated for a source S2, the detected intensity decreases.

Which is correct?

[1 mark]

Light waves from S1 Light waves from S2

A unpolarised polarised

B unpolarised unpolarised

C polarised polarised

D polarised unpolarised

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer is option A, where light waves from S1 are unpolarised and light waves from S2 are polarised.

14 A unpolarised polarised AO1

How to answer it

Investigating Light Polarisation with Polaroid Filters

What this question tests

This question assesses your understanding of transverse wave properties, specifically the phenomenon of polarisation and how polarising filters (Polaroids) interact with unpolarised versus plane-polarised light. It tests AO1 knowledge recall and application to experimental observations.

Question 1.4

Exam Breakdown & Analysis

✅ Correct Answer: A

Light from S₁ is unpolarised, and light from S₂ is polarised.

Mark Awarded: 1 / 1 mark (AO1)

💡 Key Knowledge

  • Unpolarised light: Electric field oscillations occur in all planes perpendicular to the direction of energy propagation. Rotating a polariser blocks half the intensity equally across all angles, keeping the detected intensity constant.
  • Plane-polarised light: Oscillations are restricted to a single plane. Rotating a polariser changes the component of the electric field passing through, causing the intensity to vary (and drop as it approaches extinction according to Malus's law).

🧠 Exam Technique

Break down the two scenarios independently to quickly eliminate wrong options:

  • "Intensity does not change when rotated" immediately points to unpolarised light. (Eliminates options C and D).
  • "Intensity decreases" when rotated points to polarised light interacting with the filter's transmission axis. (Confirming option A over B).

❌ Common Errors

  • Assuming that any light passing through a polaroid becomes polarised and therefore its intensity must change upon rotating a second filter—forgetting that the first source might already emit unpolarised light whose average transmitted intensity remains constant.
  • Confusing wave interference or diffraction patterns with polarisation effects.

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.