Polarisation

Question 1

What is polarisation?

Answer 1

• Particle oscillations occurring only in one of the directions perpendicular to the direction of wave travel
• Can only occur in transverse waves because transverse waves oscillate in any plane perpendicular to the energy transfer

Question 2

What happens when transverse waves are polarised?

Answer 2

• Vibrations are restricted to one direction by polarising filter
• These vibrations are still perpendicular to the direction of energy transfer
• In real life,the intensity of the unpolarised electromagnetic wave reduces after it passes through a polarising filter

Question 3

At which angles are the maximas and minimas of light intensity found when a light source is shone at two polarisers (Polarisers A and B) and polariser B is rotated to those angles

Answer 3

• When polariser B is rotated 0, 180 and 360 degrees, the light intensity is at a maximum
• When polariser B is rotated 90 and 270 degrees, the light intensity is at a minimum

Question 4

What are polaroid sunglasses?

Answer 4

• Polaroid sunglasses are glasses containing lens with polarising filters with transmission axes that are
  vertically oriented (glasses do not allow any horizontally polarised light to pass through)

Question 5

What happens when light reflects off a reflective surface like surface of water?

Answer 5

• Undergoes partial plane polarisation
• This means if the surface is horizontal, a proportion of the reflected light will oscillate more in the horizontal plane than the vertical plane

Question 6

What are polaroid sunglasses useful for?

Answer 6

• Reducing glare from partial plane polarisation
• Partially-polarised light will be eliminated by the polarising filter in polaroid sunglasses
• So objects under the surface of the water can be viewed more clearly

Question 7

How is polaroid photography similar to polaroid sunglasses?

Answer 7

• Polarising filters enable photographers to take photos of objects underwater
• This is because the light reflected on the surface of the water is partially polarised in the horizontal plane
• This glare is eliminated by the polarising lens
• However, the light from the underwater object is refracted by the surface of the water, not reflected
• So it is not plane-polarised so light from the underwater object is more intense than the glare and shows up much
  more brightly in the photo

Question 8

How does polarisation of radio and microwave signals work?

Answer 8

• Radio and television services are broadcast either horizontally-polarised or vertically-polarised
• Therefore, the reception aerial needs to be mounted flat (horizontal), or on its side (vertical)
• The particular orientation of an aerial will depend on the transmitter it is pointing towards and the polarity of the services being broadcast (Ariel needs to match orientation of transmitter)