5.3- TOTAL INTERNAL REFLECTION Flashcards
When a light ray travels from glass into air, where does it refract towards?
refracts away from the normal
What happens if the angle of incidence is increased to a certain value known as the critical angle?
light ray refracts along the boundary
What does the light ray undergo if the angle of incidence is increased further than the critical angle?
total internal reflection at the boundary, same as if boundary were replace by plane mirror
In general, when does total internal reflection only happen if…? (2)
incident substance has a larger refractive index than the other substance
angle of incidence exceeds the critical angle
How is the angle of refraction 90° at the critical angle?
as the light ray emerges along the boundary
What equation can be given as sin90 = 1?
sinθ(small c) = n2 / n1
n1- refractive index of incident substance
n2- refractive index of other substance
What happens to light when in enters a diamond?
it’s split into the colours of the spectrum
What is the refractive index of diamond like?
very high refractive index of 2.417
What can diamond do as it has a very high refractive index?
separates colours more than any other substance does
What does the high refractive index of diamond give it?
critical angle of 24.4°
What does diamond having a critical angle of 24.4° mean and how does it cause it to look?
light ray in diamond may be totally internally reflected many times before it emerges, which means its colours spread out more and more
so diamond sparkles with different colours
Example of where optical fibres are used in?
medical endoscope
What are optical fibres used in medical endoscopes for?
to see inside the body
What else is optical fibres used for other than endoscopes?
in communications to carry light signals
What happens to a light ray when it reaches a fibre boundary in an optical fibre?
light ray totally internally reflected each time it reaches fibre boundary, even where fibre bends, unless radius of bend too small
What is the angle of incidence like at each point where the light ray reaches the boundary? (optical fibres)
at each point where light ray reaches boundary, angle of incidence exceeds critical angle of fibre
What does a communication optical fibre allow a pulse of light to do?
allows pulse of light that enters at one end, form transmitter, to reach receiver at other end
What do communication optical fibres need to be like?
highly transparent
Why do communication optical fibres need to be highly transparent?
to minimise absorption of light
What would happen if communication optical fibres were not highly transparent, and so didn’t minimise absorption of light?
amplitude of pulses reduces progressively further they travel in fibre
What does each fibre consist of? (optical fibres)
core surrounded by layer of cladding of lower refractive index to reduce light loss from core
What would light loss do? (optical fibres)
would reduce amplitude of pulses
Where does the total internal reflection take place? (optical fibres)
core-cladding boundary
What happens at any point where two fibres are in direct contact if there were no cladding? (optical fibres)
light would cross from one fibre to the other