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Module 4 - Chapter 11 - Waves 1 II - Coggle Diagram
Module 4 - Chapter 11 - Waves 1 II
EM waves
Don't need a medium to travel through
Electric and magnetic fields oscillating at right angles to eachother
Polarisationg of EM wave
Unpolarised EM wave can be polarised using filters called polarisers
Each filter only allows wave with a particular orientation through
Properties
Transverse
Can be reflected, refracted, diffracted and polarised
Refractive index
Tells you how much the wave is refracted by as it passes through the boundary
n = sol through vacuum/ sol through material)
Tells you how much the wave slows down
sol through a material will always be less than the sol through a vacuum
Snells law
Total internal reflection
When all light is reflected back into the original medium, and no light energy is refracted out of the medium
Conditions
Light must be travelling through the medium wtih a higher refractive index as it strikes the boundary with a medium will low refractive index
Angle at which light strikes must be above the critical angle - angle of incidence for which the angle of refraction is 90
Polarisation
Particles osciallte along one direction only, wave is confined to a single plane
Light from an unpolarised light source is made up of oscillations in many possible planes.
Since light is transverse, oscillations are always 90 degrees to the direction of energy transfer
ongitudinal waves can't be polarised as their oscillations are only in one plane
Partial polarisation
When transverse waves reflect off a surface they become partially polarised
Waves oscillate in one particular plane, but wave isn't completely plane polarised
Microwaves
Metal grille can be used
When grille is parallel to microwave polarisation, grille blocks all microwave transmissions
Free electrons in grille can cancel out the electric field in the same direction as the grille and absorb it
Horizontal electric field passes if grille is positioned vertically
Investigating
Position two polarising filters vertically and shine unpolarised light onto the first filter
Filter polarises light vertically,aligning light's vibration direction with the filter's transmisisons axis
Second filter allows all light through
Rotating second filter gradually decreases intensity of transmitted light
Complete 90 degrees results in no light transmission
Phase difference
Describes the difference between displacement of particles along a wave, different between displacements of particles on different waves
Particles perfectly in step with eachother are in phase, their phase difference is 0 degrees
Particles seperated by one whole wavelength have a phase difference of 360 degrees
Particles osciallting completely out of step (one reaches peak when the other reaches a trough) are in antiphase, and have a phase difference of 180 degrees
