Waves

Question 1

What is polarisation?

Answer 1

• Polarisation is when particle oscillations occur in a single plane perpendicular to the direction of wave propagation

Question 2

What types of waves can polarisation occur in and why?

Answer 2

• Polarisation can only occur in transverse waves
• This is because transverse waves oscillate in any place perpendicular to the propagation direction
• In longitudinal waves, the waves oscillate in only one plane parallel to the propagation direction, hence there is nothing to polarise (already only one plane)

Question 3

What happens to a wave when it is polarised?

Answer 3

• Vibrations are restricted to one direction
• These vibrations are still perpendicular to the direction of propagation

Question 4

How can waves be polarised?

Answer 4

• Waves can be polarised through a polariser or polarising filter
• This allows oscillations in a certain plane to be transmitted

Question 5

What other method can be used to polarise light waves?

Answer 5

• Light can be polarised through reflection, refraction and scattering

Question 6

How can polarisation be used to measure light intensity?

Answer 6

• If an unpolarised light source is placed in front of two identical polarising filters, A and B, with their transmission parallel:
• Filter A will polarise the light in a certain axis
• All of the polarised light will pass through filter B unaffected (both filters polarising in the same direction)
• In this case, the maximum light intensity is transmitted
• As the polarising filter B is rotated anticlockwise, the intensity of the light observed changes periodically depending on the angle B is rotated through

Question 7

When is maximum and minimum light transmitted during polarisation?

Answer 7

• When A and B have their transmission axes parallel to each other, the maximum light intensity is transmitted
• When A and B have their transmission axes perpendicular to each other, the minimum light intensity is transmitted (no light)

Question 8

What happens to the light intensity in real life during polarisation?

Answer 8

• In real life, the intensity of the unpolarised wave reduces as it passes through a polarising filter