5.3 Flashcards
what happens when the incidence ray is at the critical angle
it reflects long the boundary e.g sin 90
what happens if the angle of incidence is greater than the critical angle
the light ray undergoes total internal reflection and acts as if the boundary was a mirror
when can total internal reflection take place
if the incident substance has a larger reactive index - more dense
the angle of incidence exceeds the critical angle
why do diamonds sparkle
splits the colours into the spectrum
has a very high refractive index of 2.417 so s[plits colours more than any other substance
high reactive index so small critical angle pf 24.4
light may be totally internally reflected many times before it is release
what does a high refractive index mean
small critical angle
what are optical fibres
used in medical endoscopes to see inside the body and in communications to carry light signals
communications optic fibre
allows pulses of light to enter from a transmitter at one end to a receiver at the other
such fibres need to be highly transparent to minimise absorption of light which would reduce the amplitude of the pulses progressively the futer they travel through the fibre
what does each fibre consist of
a core surrounded by a layer of cladding of a lower refractive index to reduce light loss from the core
light loss would also reduce the amplitude of the pulses
when does total internal refection take place in the fibre
at the core cladding boundary
what would happen if there was no cladding
light would cross from one fibre to another meaning the signals wouldn’t be secure as they could reach the wrong destination
why must the core be very narrow
to prevent model dispersion (multi path)
what is modal dispersion
occurs in a wide core
a pulse of light sent along a wide core would become longer than ought to be .
if it was too lo g it would merge with the next pulse
when does pulse dispersion occur
if white light is used instead of monochromatic light
why does pulse dispersion due to white light occurs
thi material dispersion or spectral dispersion is because the speed of light in the glass of the optical fibre depends on the wavelength of the light travelling through it
violet travel more slowly in glass than red
difference in speed would cause white light pulses in optical fibres to become longer as violet falls behind the faster red
mobochramatic light to be used to prevent pulse merging
what is the medical endoscope made up of
2 bundles of fibres
one bundle of fibres is used for a light
the other is used to form an image with a lens on the end
in order for an image to be observed this fibre bundle needs to be coherent which means that the fibre ends at each end are in the same relative position
