Diffraction and polarisation

what is diffraction?

what is diffraction?

when waves pass through a gap or travel around an obstacle, they spread out

what changes in diffraction?

nothing lmao

when are diffraction effects most significant? (that feels significant)

when the size of the gap or obstacle is the same as the wavelength of the wave

what is polarisation?

when the particles oscillate along one direction only so the wave is confined to a single plane, so the wave is plane polarised

what is unpolarised light like?

oscillations in many possible planes where the oscillations are always perpendicular to the direction of energy transfer

why can’t i polarise longitudinal waves?

the oscillations are already limited to only one plane (the direction of energy transfer) so they cannot be polarisedwht

what is partial polarisation?

• happens when transverse waves reflect off a surface

• more waves are oscillating in one particular plane but the wave is not completely plane polarised

• eg. light reflected off the surface of water

what do polarising filters do?

they only allow waves with a particular orientation through

what happens when you put two Polaroid filter together at 90 degrees?

the intensity of the light will be 0 because the first filter only allowed waves with one specific orientation to pass through, so the wave was plane polarised, so if the second filter is placed at 90, the already polarised wave won’t be able to pass through it, so the intensity will be 0

polarisation in comms transmitters

some transmitters transmit vertically plane polarised waves and others nearby transmit horizontally polarised waves. an aerial aligned to detect vertically plane polarised waves will therefore suffer less interference from horizontally polarised waves

how does one polarise a microwave?

• microwaves produced artificially tend to be plane polarised, but unpolarised microwaves can be polarised by placing a metal grille in between the microwave transmitter and the microwave receiver

• microwave ovens contain a metal sheet with lots of holes, which allows visible light to pass through but not microwaves