optics Flashcards
what is the equation of refractive index?
sin incidence/ sin refraction
what does coherent mean?
there is a constant phase difference
what does monochromatic mean?
the light wave contains only one wavelength of light
what is the effect of a greater wavelength of light on single slit interference
-the fringes are wider
what is the effect of a narrower slit on single slit interference
-the fringes are wider
where does total internal reflection occur in optical fibres
at the core cladding boundary
why does total internal reflection occur in fibres
to prevent the light reaching the wrong direction as the signals would not be secure
why is the core narrow on an optical fibre
to prevent modal dispersion so the first pulse of light doesn’t merge with the second pulse
name the two requirements for light sources to be coherent
same wavelength
constant phase difference
when does refraction not occur
if the incident light ray is along the normal
at a boundary between two transparent substances how does a light ray bend
towards the normal if going into a more dense substance
away from the normal if going into less dense substance
state three advantages of an optical fibre having a smaller core
- less light is lost
- better signal quality
- less change of angle between each reflection
state an application of optical fibres
communications
when will total internal reflection occur
if the incident substane has a larger refractive index than the other substanece
if the ange of incidence exceeds the critical angle
what is modal dispersion
lengthening of light waves
due to undergoing repeaditly total internal reflection having to travel longer distance than light rays that undergo fewer internal reflections
what happens to a signal in an optical fibre when it undergoes absorbance
part of signals energy absorbed by fibre
reduces amplitude of signal
what is a material dispersion
light rays will travel at different speeds across the fibre this can lead to pulse broadening
what is pulse broadening
where the received signal is broader
than the original transmitted signal
how do you prevent modal dispersion
making the core very narrow
so difference in path lengths smaller
how are the fringes formed in a double slit experiment
due to interference of light
what occurs at bright fringes in double slit experiment
light waves from each slit arrive in phase with each other so light from each slit reinforces each other
what occurs at dark fringes in double slit experiment
light waves from the two slits arrive 180 degrees out of phase so light from one slight cancels out light from the other
what is a coherent source of light
one which emits waves of same frequency with constant phase difference
describe white light fringe from a single slit
central fringe is white
inner fringe blue inner side red outer side
outer fringes merge into white light getting fainter with bigger distance from centre
how will diffracted waves spread out more
gap is narrower
wavelength is larger
outline a single slit diffraction pattern
central fringe twice as wide as outer fringes
peak intensity of each fringe decreases with increasing distance from centre
each outer fringe same width
outer fringes less intense than central fringe
