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Waves

Polarisation

  • 3 things to know
  • Papers 2 and 3

Overview

Recall questions on polarisation and plane polarised waves, why only transverse waves can be polarised, and demonstrating polarisation with polarising filters, crossed polarisers and microwaves with a metal grille.

What you need to know

Answer each one before you reveal it.

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Key term

Explain why longitudinal waves cannot be polarised, and define a plane polarised wave.

Key term

How do a metal grille and polarising filters demonstrate polarisation, and what happens when two polarising filters are crossed at 90°?

Key term

What happens when unpolarised light passes through two polarising filters whose transmission axes are crossed at 90° to each other?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Which type of wave can be polarised, and which cannot?

    Model answer

    Only transverse waves can be polarised; longitudinal waves cannot be polarised.

  2. 2

    What is polarisation of a wave?

    Model answer

    Polarisation is the restriction of wave oscillations to a single plane containing the direction of propagation.

  3. 3

    Describe how polarisation of light can be demonstrated using polarising filters.

    Model answer

    Two polarising filters are used; rotating the second filter varies the transmitted intensity from maximum (axes parallel) to zero (axes perpendicular).

  4. 4

    Define a plane polarised wave.

    Model answer

    A transverse wave in which the oscillations occur in only one plane containing the direction of propagation.

  5. 5

    Explain why longitudinal waves cannot be polarised.

    Model answer

    Only transverse waves can be polarised because polarisation requires oscillations perpendicular to the direction of propagation; longitudinal waves oscillate parallel to the direction of travel.

  6. 6

    How do polarising filters demonstrate the polarisation of light?

    Model answer

    They transmit only oscillations in one plane, blocking oscillations in other planes.

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