11.3 + 11.4 Reflection, refraction, diffraction, polarisation Flashcards
what is reflection?
when a wave changes direction at a boundary between two media, remaining in the original medium
* wavelength, frequnecy do not change
what is a wavefront?
Lines of constant phase
what is refracation?
when a wave changes speed as it changes direction at the boundary of two media
* frequnecy the same
* wavespeed and wavelength change
will always be partial reflection
what happens when waves moves to denser mediums
- normal waves: speed up, move away from the normal
- EM waves slow down, move towards the normal
what is diffraction?
the spreading out of a wave front as it passes through a gap
* hyeogens principle: when a wave is disturbed each point where there is a disturbance becomes a source for a spherical wave
maximim difraction when gap is same size as incident wavelength
What is polarisation ?
Can only be done to transverse waves, applying a filter to light
What is a plane polarised light?
A transverse wave where oscillations are limited to only one plane
What happens when two polarised filters are perfectly aligned ?
What happens when two Polaroid filters are at 90° to each other?
Describe the use of Polaroid sun glasses
- light is horizontally polarsied (from water/metal surfaces)
- sunglasses have vertically alligned filtesr blobking all this polarised light
- this reduces the bright glare
What happens to the wavefronts in diffraction?
Describe refraction in terms of wavefronts
Part of wavefronts change speed first causing the change in direction, when at an angle to the normal
What are the refraction rules for EM waves and mechanical waves?
what are the rules for diffraction?
- wave speed, wavelength: do not change
- the longer the wavelength the more the wave spreads out
- the smaler the gap relative to the wavelength, the greater the diffraction
what is polarisation?
- a property of transverse waves
- defines the plane of oscillation of the wave
what is the plane of polarisation of an EM wave?
the plane in which the electric field vibrates
how is light (EM waves) polarised with filters?
- plane of allignment of the filter is the plane in which E-field oscillations pass through
- transmitted light is polarised in the same plane
allows all components of waves in that certain direction not just E fiel
what is unpolarised light?
- **wave trains **(a group of waves of equal or similar wavelengths travelling in the same direction)
What is Malus Law?
how is light polarised by reflection?
- on metal surfaces and water
- polarised in the horizontal plane
How do polarising filters work?
- unpolarised light from lamp
- p1 polarises the light in the vertical plane
- p2 polarises light int the horizontal plane
- but there is no component of vertically plane polarised light that lays in the horizontal direction
when in the maximum intensity emitted from 2 polarising filtres?
when they have no effect ( are alligned in the same plane)
Polarising filters MCQ
What is the wavelength formula?