11.4 Diffraction and Polarisation Flashcards
What is diffraction?
- Diffraction is the bending and spreading of waves when they encounter an obstacle or pass through a gap. It occurs with all types of waves, including sound, water, and electromagnetic waves (such as light and radio waves).
- The speed, wavelength and frequency does not change when diffraction occurs.
- Diffraction effects are most significant when the size of the gap or obstacle is about the same as the wavelength of the wave.
What is polarisation?
Polarisation is the process of restricting the oscillations of a transverse wave to a single plane. It occurs only in transverse waves (e.g., light, water waves, electromagnetic waves) and not in longitudinal waves (like sound), because longitudinal waves oscillate parallel to their direction of travel.
This ‘plane of oscillation’ contains the oscillation of the particles and the direction of travel of the wave. The wave is said to be “plane polarised”.
What kind of waves cannot be polarised and why?
Longitudinal waves.
Polarisation occurs when the vibrations of a wave are restricted to a single direction perpendicular to the wave’s propagation.
Longitudinal waves, the oscillations are parallel to the direction of propagation so since there is no perpendicular oscillation component, filtering it in a specific direction (which is how polarisation works) is not possible.
What is partial polarisation?
Partial polarisation occurs when a wave is not completely polarised but has a preference for vibrating in one particular direction more than others. Unlike full polarisation, where vibrations occur in a single plane, a partially polarised wave still has vibrations in multiple planes, just with an unequal intensity distribution.
Some sunglasses contain polarising filters. These only allow light oscillating in one plane to pass through them, reducing the glare reflected off flat surfaces like lakes.
