Polarisation

Question 1

When viewing a source of light through two polarisers, rotating one of the polarisers through 90 degrees reduces the transmitted intensity to zero. Rotation through a further 90 degrees results in transmission of light again. Why does this happen?

Answer 1

Light from the source is unpolarised. The first polariser transmits light with one polarisation, say vertical. If the second polariser is also aligned to transmit vertically polarised light, then light from the source will be visible through the two polarisers. Rotating either polariser through 90 degrees means that the light transmitted by the first polariser will not be transmitted by the second, so no light is seen.

Question 2

What is polarisation a property of?

Answer 2

Transverse waves only

Question 3

If a wave is plane-polarised, what does this mean?

Answer 3

The direction of oscillation remains fixed

Question 4

If a wave is unpolarised, what does this means?

Answer 4

There is transverse waves oscillations in all directions

Question 5

What happens when unpolarised light passes through a polarising filter?

Answer 5

It is polarised

Question 6

How can the polarisation of radio waves be detected?

Answer 6

If you rotate the aerial, the aerial will pick up the strongest signal when it is set up parallel to the plane of polarisation of the radio waves

Question 7

Why does a microwave (or radio) receiver aerial needs to be aligned vertically in order to detect vertically polarised microwave radiation?

Answer 7

If the microwaves are, say, vertically polarised, then the aerial must also be aligned vertically so that the oscillating electric field of the microwaves can cause electrons to be accelerated up and down the aerial wire. This corresponds to absorption.

Question 8

When light is polarised, what does it oscillate in?

Answer 8

One plane only

Question 9

When light is unpolarised, what does it oscillate in?

Answer 9

A randomly varying plane

Question 10

When light passes through a polarising filter, what is transmitted?

Answer 10

Light of one plane of polarisation

Question 11

Why do skiers use polarising filters to cut down glare from sunlight reflected off snow?

Answer 11

Reflected light is partially polarised, so filters are used to cut out light of this plane of polarisation