Polarisation
Cambridge A-Level Physics (9702) · Unit 7: Waves · 6 flashcards
Polarisation is topic 7.5 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 7 — Waves , alongside Progressive waves, Transverse and longitudinal waves and Doppler effect for sound waves. In one line: Polarisation is a phenomenon exhibited by transverse waves only. Longitudinal waves cannot be polarised because their oscillations are parallel to the direction of propagation.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 6 flashcards — 3 definitions, 2 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
What type of wave exhibits polarisation
Polarisation is a phenomenon exhibited by transverse waves only. Longitudinal waves cannot be polarised because their oscillations are parallel to the direction of propagation.
What the Cambridge 9702 syllabus says
Official 2025-2027 spec · AS LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- understand that polarisation is a phenomenon associated with transverse waves
- recall and use Malus’s law (I = I0 cos2θ ) to calculate the intensity of a plane-polarised electromagnetic wave after transmission through a polarising filter or a series of polarising filters (calculation of the effect of a polarising filter on the intensity of an unpolarised wave is not required)
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Polarisation
- › Specify wavelength as the distance between two adjacent wavefronts or the minimum distance between points in phase.
- › Distinguish between displacement (instantaneous) and amplitude (maximum). Nodes have zero amplitude and never move from the equilibrium position.
- › Always use the term 'adjacent' or specify the 'minimum distance' between two points in phase, such as adjacent wavefronts or crests.
- › Always refer to 'particle oscillations' being parallel to the 'direction of energy transfer' for longitudinal waves.
- › Define stationary waves as the superposition of two waves of the same frequency and amplitude traveling in opposite directions.
What type of wave exhibits polarisation?
Polarisation is a phenomenon exhibited by transverse waves only. Longitudinal waves cannot be polarised because their oscillations are parallel to the direction of propagation.
Define polarisation in the context of transverse waves.
Polarisation refers to the restriction of the oscillations of a transverse wave to a single plane. This plane contains the direction of propagation.
State Malus's Law.
Malus's Law states that the intensity (I) of plane-polarised light after passing through a polariser is given by I = I₀cos²θ, where I₀ is the initial intensity and θ is the angle between the polariser's transmission axis and the plane of polarisation of the light.
A polarising filter is rotated from 0° to 90° relative to the plane of polarised light. How does the transmitted intensity change?
As the angle increases from 0° to 90°, the transmitted intensity decreases. At 0°, the intensity is maximum (I₀), and at 90°, the intensity is zero.
Plane-polarised light of intensity 20 W/m² passes through a polarising filter oriented at 30° to the plane of polarisation. What is the intensity of the transmitted light?
Using Malus's Law: I = I₀cos²θ = 20 W/m² * cos²(30°) = 20 W/m² * (√3/2)² = 20 * (3/4) = 15 W/m².
Unpolarised light is incident on two polarising filters. The first filter has its transmission axis vertical, and the second filter has its transmission axis at 45° to the vertical. Describe the light after passing through both filters, with explanation.
The first filter polarizes the light vertically. Then Malus's Law tells us the second reduces the intensity by cos²(45°) = (√2/2)² = 1/2. The light is plane polarised at 45° to vertical, and has intensity I = I₀ * 1/2, where I₀ is the intensity of the polarised light after passing through the first filter.
Review the material
Read full revision notes on Polarisation — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 7 — Waves
Polarisation sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Polarisation deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Polarisation deck
Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.
Study Mode
Rate each card Hard, Okay, or Easy after flipping.