Wavs & Optics- Polarisation

Question 1

Polarisation

Answer 1

• Waves are travelling disturbances that carry energy from one place to another along a certain direction, called the propagation direction.
• If the displacement is parallel to the propagation direction, the wave is a longitudinal wave. Sound waves are an example of longitudinal waves.
• In other waves, the displacement is perpendicular to the propagation direction. These are called transverse waves.
• The displacement of a transverse wave can be in any direction in the plane that is perpendicular to the propagation direction.
• If the displacement of a transverse wave are restricted wave are restricted to one line, then we say it is linearly polarised.

Question 2

Polarising Filters

Answer 2

• linearly polarised waves can be created by passing unpolarized waves through a polarising filter.
• Polarising filters only transmit oscillations in a certain plane.
• polarising filters for electromagnetic waves can be made from materials such as polaroid.

Question 3

Polarised Electromagnetic Waves

Answer 3

• Electromagnetic waves consist of oscillating electric and magnetic that are perpendicular to each other and the direction of propagation
• By convention, the polarisation direction of electromagnetic waves is defined to be the direction in which the electric field oscillates.
• Polarised electromagnetic waves are often used for the transmission of signals. Antennas can usually only transmit and receive waves in a given polarisation, which reduces unwanted noise from other signals.

Question 4

Polarisation from reflection

Answer 4

• When unpolarised waves are reflected from a dielectric material, the reflected waves become partially polarised.
• If a polaroid filter is used to view the reflected light, the intensity of the light will vary when the filter is rotated.
• The amount of variation depends upon the angle of incidence of the light on the material from which it was reflected.