OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(c) plane polarised waves; polarisation of electromagnetic waves
Full specification wording
Electromagnetic waves: (c) plane polarised waves; polarisation of electromagnetic waves
A plane polarised wave has oscillations confined to a single plane.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 3 of 6
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A plane polarised wave has oscillations confined to a single plane. For an electromagnetic wave, the electric field vector oscillates in one specific plane containing the direction of propagation. Unpolarised light features electric field oscillations in multiple planes perpendicular to the direction of travel. Polarisation can be achieved by passing light through a polarising filter, which transmits only the component of the electric field aligned with its transmission axis. If unpolarised light passes through a polariser, the transmitted intensity is halved. When this polarised light of intensity I₀ strikes a second filter (an analyser), the transmitted intensity I is given by Malus's law: I = I₀ cos²θ, where θ is the angle between the transmission axes. Polarisation provides crucial evidence that electromagnetic waves are transverse.
What earns the marks
- Defines a plane polarised wave as one where oscillations are confined to a single plane.
- States that for electromagnetic waves, the electric field vector oscillates in a single plane containing the direction of propagation.
- Explains that unpolarised light has electric field oscillations in many planes perpendicular to the direction of travel.
- Applies Malus's law (I = I₀ cos²θ) correctly, identifying I₀ as the maximum intensity of the polarised light incident on the analyser.
- Concludes that the ability to be polarised is evidence that electromagnetic waves are transverse.
Common mistakes and how to put them right
Using the initial unpolarised intensity as I₀ in Malus's law.
Put it right: I₀ is the intensity of the already polarised light incident on the analyser; the first polariser halves the unpolarised intensity.
Stating that polarisation proves waves are electromagnetic.
Put it right: It proves they are transverse; other transverse waves can also be polarised.
Believing a polarising filter blocks all light.
Put it right: It transmits the component of the electric field parallel to its transmission axis.
Exam tips
- When dealing with two filters, remember to halve the intensity of unpolarised light through the first polariser before applying Malus's law for the second.
- Sketch the planes of oscillation to help visualise the effect of polarising filters.
- Explicitly link the phenomenon of polarisation to the transverse nature of electromagnetic waves in explanation questions.
Try the lesson
The start of the Electromagnetic waves: (c) plane polarised waves; polarisation of electromagnetic waves lesson, made from checked teaching notes for this specification point.
Listen
A plane polarised wave has oscillations confined to a single plane. For an electromagnetic wave, the electric field vector oscillates in one specific plane containing the direction of propagation. Unpolarised light features electric field oscillations in multiple planes perpendicular to the direction of travel. Polarisation can be achieved by passing light through a polarising filter, which transmits only the component of the electric field aligned with its transmission axis. If unpolarised light passes through a polariser, the transmitted intensity is halved. When this polarised light of intensity I₀ strikes a second filter (an analyser), the transmitted intensity I is given by Malus's law: I = I₀ cos²θ, where θ is the angle between the transmission axes. Polarisation provides crucial evidence that electromagnetic waves are transverse. A strong answer earns marks for these points. Defines a plane polarised wave as one where oscillations are confined to a single plane. States that for electromagnetic waves, the electric field vector oscillates in a single plane containing the direction of propagation. Explains that unpolarised light has electric field oscillations in many planes perpendicular to the direction of travel. Applies Malus's law (I = I₀ cos²θ) correctly, identifying I₀ as the maximum intensity of the polarised light incident on the analyser. A common slip: Using the initial unpolarised intensity as I₀ in Malus's law. Instead, I₀ is the intensity of the already polarised light incident on the analyser; the first polariser halves the unpolarised intensity. Exam tip: When dealing with two filters, remember to halve the intensity of unpolarised light through the first polariser before applying Malus's law for the second.
Key words
Say what each word means before you turn the card.
Plane polarised wave
Try answering aloud or in your head before turning the card.
Malus's law
Try answering aloud or in your head before turning the card.
See every definition
- Plane polarised wave
- A wave in which the oscillations are confined to a single plane.
- Malus's law
- The transmitted intensity I is given by I = I₀ cos²θ, where θ is the angle between the transmission axes.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Electromagnetic waves: (c) plane polarised waves; polarisation of electromagnetic waves
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge