Waves Flashcards
What is coherent
no phase difference
monochromatic
single wavelength
wave theory to explain dark and light spots
light diffracts at slits
waves superpose
constructive wave front creates area of bright spots, in phase so reinforce, crest meet
deconstructive wave front creates area of dark spots, out of phase so cancel out, trough meet
2 requirements for light source to be coherent
same phase
waves must be of same frequency
same wavelength
2 parts of a fibre
cladding and core
why is optic fibre thin
less light lost
better quality
less refraction out core
more chance of TIR
improve data transfer
transverse wave
direction is perpendicular to energy transfer
only transverse waves can be polarised
longitudinal wave
direction is parallel to energy transfer
superposition
two waves cross paths and the displacements of each add up
Young’s Double Slit experiment
shows the wave nature of light
illuminate two close spaced slits which act as coherent light source
alternate bright and dark fringes on screen
fringes are evenly spaced
bright fringe-light from each slit is in phase with each other
dark fringe-lights are in antiphase
w = λD/s
to measure w, measure across several dark fringes, centre to centre then divide by number of fringes
white light YDS experiment
central fringe is white
inner fringes are blue on inside , red on outside
outer fringes are white
diffraction spreads more if?
gap is made narrower
wavelength is made larger
(the gap needs to be similar in size to wavelength for it to diffract)
single slit diffraction
interference pattern
central bright fringe
dark and bright fringes on either side
central fringe is twice as big as the outer fringes
diffraction grating
monochromatic light is directed normally at diffraction grating, light is transmitted in certain directions
d sin θ = n λ
