KCL Section 1: Plane polarisation (Waves and Photons)

Question 1

State the definitions of transverse and longitudinal waves

Answer 1

Transverse waves oscillate perpendicular to the direction of propagation of the wave.

Longitudinal waves oscillate parallel to the direction of propagation of the wave.

Question 2

What are 4 methods of polarising light?

Answer 2

A polaroid filter (light through a phone screen or sunglasses)
Reflection off a surface (light bouncing off snow or water)
Refraction through a substance (light passing through plastic)
Scattering through a substance (light through the atmosphere)

Question 3

What is plane polarised light?

Answer 3

Oscillations of an electromagnetic wave in one plane only which includes direction of propagation/energy transfer.
OR
Oscillations of an electromagnetic wave in one direction only which is perpendicular to direction of propagation/energy transfer.

Question 4

Put the sentences in the correct order:
A polarising filter is rotated until it allows no light through to the eyepiece
Unpolarised light is produced
The angle of the rotating polarising filter is recorded
The light passes through a polarising filter, which limits the oscillations to a single plane

Answer 4

B
D
A
C

Question 5

Name three uses of polarisation

Answer 5

Identification and analysis of optically active chemicals
Liquid crystal displays
Sunglasses and snow goggles
TV and radio signals
3D film glasses

Question 6

How do LCDs work?

Answer 6

Two filters are placed 90 degrees to each other ⇒ no light passes through both

Liquid crystals in between the filters rotate the plane of the polarised light when there is a current across them ⇒ light can pass through

Question 7

Why did storms stop people from being able to watch the TV or listen to the radio?

Answer 7

TV and radio signals are polarised, so the detector needs to be aligned with the plane of the polarised wave to receive the maximum signal strength. Therefore, if wind moved the detector so that it was no longer aligned with the plane of the polarised wave the signal strength w ould be poor.

Question 8

What can intensity be called?

Answer 8

Intensity is sometimes called radiation flux density.

Question 9

What does intensity measure?

Answer 9

Intensity measures how much energy reaches an area per second.

Question 10

Intensity formula?

Answer 10

intensity = power/area