Can sound waves be polarised?

No, because sound in air is longitudinal, and polarisation is a phenomenon of transverse waves only.

What does a single polarising filter do to a beam of unpolarised light?

It transmits only the component of the oscillation that is parallel to its transmission axis, so the emerging light is plane-polarised and its intensity is roughly halved.

What is observed when unpolarised light passes through two polarising filters whose transmission axes are at right angles?

Almost no light emerges, because the first filter polarises the light in one plane and the second transmits only the perpendicular component, which is zero.

Describe how the brightness changes as one of two polarising filters is slowly rotated through a full turn.

The brightness rises to a maximum when the axes are parallel and falls to zero when they are perpendicular, and each of these happens twice in a complete turn.

CCEA A-Level Physics 1210

Physical Quantities, Scalars and Vectors

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Waves

Polarisation

3 things to know
Unit AS 2

Overview

Plane-polarised wave, unpolarised light and how polarising sunglasses cut glare from a wet road.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain how polarising sunglasses cut glare from a wet road.

Key term

What is a plane-polarised wave?

Key term

Why can only transverse waves be polarised?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a plane-polarised wave?
Model answer
A plane-polarised wave is one in which the oscillations take place in only one plane, and that plane contains the direction of travel.
2
Why can only transverse waves be polarised?
Model answer
A longitudinal wave oscillates along its direction of travel, so there is only one possible plane of oscillation and nothing to restrict, whereas a transverse wave can oscillate in any plane perpendicular to travel and can be confined to one of them.
3
Can sound waves be polarised?
Model answer
No, because sound in air is longitudinal, and polarisation is a phenomenon of transverse waves only.
4
What does a single polarising filter do to a beam of unpolarised light?
Model answer
It transmits only the component of the oscillation that is parallel to its transmission axis, so the emerging light is plane-polarised and its intensity is roughly halved.
5
What is observed when unpolarised light passes through two polarising filters whose transmission axes are at right angles?
Model answer
Almost no light emerges, because the first filter polarises the light in one plane and the second transmits only the perpendicular component, which is zero.
6
Describe how the brightness changes as one of two polarising filters is slowly rotated through a full turn.
Model answer
The brightness rises to a maximum when the axes are parallel and falls to zero when they are perpendicular, and each of these happens twice in a complete turn.

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