AQA AS Level Physics Paper 1, June 2023: Question 3

6 marks · Medium difficulty · Extended Answer

Explain why a student wearing Polaroid sunglasses can see submerged objects in a lake more clearly, by describing unpolarised waves, polarisation, and the relative effect of the sunglasses on surface reflection and light from submerged objects.

Practise this question

Question

An exam question asking a student to explain why wearing Polaroid sunglasses makes it easier to see submerged objects in a lake. The student must describe unpolarised waves, explain polarisation, and discuss the relative effect of Polaroid sunglasses on horizontally polarised surface reflection and unpolarised light from submerged objects. The question is worth 6 marks and provides answer lines below.
Question text

03 A student sits near a lake on a sunny day.

Some sunlight is reflected from the surface of the lake. Sunlight is also reflected from

objects submerged beneath the surface of the lake. The light reflected from the

surface makes it difficult to see the submerged objects.

Sunlight that reflects from the surface of the lake is horizontally polarised. Sunlight

that reflects from the submerged objects is unpolarised.

The student puts on a pair of Polaroid sunglasses. The amount of light he sees

reflected from the surface is significantly reduced.

Explain why the student can now see the submerged objects more clearly.

In your answer you should:

• describe the nature of an unpolarised wave

• explain what is meant by polarisation

• explain the relative effect of the Polaroid sunglasses on the light reflected from the

surface and the light reflected from the submerged objects.

[6 marks]

Mark scheme

Show the mark scheme The mark scheme outlines a 6-mark level-of-response answer divided into three key areas: Area A covering the nature of unpolarised waves with oscillations in more than one plane, Area B defining polarisation as restricting transverse wave oscillations to a single plane, and Area C detailing how Polaroid sunglasses absorb horizontally polarised light from the water's surface while transmitting the vertical component of unpolarised light from submerged objects.

Question Answers Additional Comments/Guidance Mark AO

03 The mark scheme gives some guidance as to what statements The following points are likely to be present. 6 4 ×

are expected to be seen in a 1- or 2-mark (L1), 3- or 4-mark (L2)

and 5- or 6-mark (L3) answer. Guidance provided in section 3.10 Area A (unpolarised) AO1.1a

of the ‘Mark Scheme Instructions’ document should be used to - Oscillations (or vibrations) of particles /

fields perpendicular to direction of energy 2 ×

assist marking this question.

propagation AO3.1a

- wave’s oscillations (or vibrations) exist in

Mark Criteria more than a single plane

Area B (polarisation)

All 3 areas covered in some detail. - (only) transverse waves can be polarised

66 marks can be awarded even if there is an error and/or parts - (oscillations) restricted to a single plane

of one aspect missing. - where the plane and direction of

propagation are coplanar / labelled

A fair attempt to analyse all 3 areas. If there are several diagram seen indicating polarised wave’s

errors or missing parts, then 5 marks should be awarded. oscillation in single plane and

perpendicular to the direction of

Two areas successfully discussed, or one discussed and two propagation.

4 others covered partially. Whilst there will be several gaps, Area C (polaroid)

there should only be an occasional error. - Polaroid sunglasses absorb the horizontal

One area discussed and one discussed partially, or all 3 component of the light / the light reflected

3 covered partially. There are likely to be several errors and from the water’s surface is (nearly all)

omissions in the discussion. absorbed by Polaroid sunglasses.

- Polaroid transmits the vertical component

Only one area discussed or makes a partial attempt at 2 of the light from submerged objects.

areas. - because the light from the submerged

objects is unpolarised 50% passes through

1 None of the 3 areas covered without significant error.

sunglasses to the eye.

0 No relevant analysis. - Idea that reduces surface reflection more

than light from submerged objects.

Total 6

How to answer it

Polarisation and Polaroid Sunglasses

AQA AS Level Physics • Waves • 6 Marks

What this question tests

This 6-mark extended response question tests your understanding of wave properties (specifically transverse waves), the definition and mechanism of polarization, and the practical application of polarizing filters (Polaroids) in reducing glare from reflective surfaces like water.

Exam Breakdown: 6-Mark Extended Response

Question 3 Analysis

💡 Key Knowledge (Area A & B)

  • Unpolarised wave: Oscillations or vibrations of particles/fields occur in many/multiple planes perpendicular to the direction of energy propagation.
  • Polarisation: Only applies to transverse waves. Oscillations are restricted to a single plane (which includes the direction of propagation).

✅ Correct Answer Criteria (Area C)

  • Polaroid sunglasses absorb the horizontal component of light. Since lake glare is horizontally polarised, it is nearly all blocked.
  • Light from submerged objects is unpolarised, so roughly 50% passes through the vertical transmission axis of the filter.
  • Surface reflection is reduced much more than light from underwater objects, increasing contrast.

🧠 Exam Technique (Level of Response)

This is marked using a 3-level scale (6 marks total). To secure Level 3 (5–6 marks), you must structure your answer logically, addressing all three required bullet points in detail with clear technical terminology.

❌ Common Errors

  • Stating that unpolarised light vibrates "in all directions" instead of specifying oscillations in more than a single plane perpendicular to propagation.
  • Forgetting to explain what happens to the unpolarised light from the submerged objects (failing to mention the 50 transmission/absorption split).
Mark Scheme Structure:
• Level 3 (5–6 marks): All 3 areas covered in detail with minor omissions allowed.
• Level 2 (3–4 marks): Two areas successfully discussed, or minor coverage across all three.
• Level 1 (1–2 marks): Fragmentary discussion of only one area.
• AO Breakdown: 4 × AO1 (Knowledge & Understanding) and 2 × AO3 (Application & Analysis).

Topics

Physics · 3.3 Waves

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