total internal reflection

total internal reflection

1. critical angle

   • when the angle of i is increased to this value and the light ray refracts along the boundary
   • angle of r = 90°

2. total internal reflection

   • take place when
     • incident sub refractive index > refractive index of other substance
     • angle of i exceeds the critical angle

3. optical fibres

   • used in medical endoscopes
     • contains two bundles of fibres
       • endoscope is inserted into a body cavity which is then illuminated using light sent through one of the fibre bundles
         • a lens on the end of the other fibre bundle is used to form an image of the body cavity on the end of the fibre bundle
   • used in comms to carry light signal
     • allow pulses of light that enter from transmitter to reach the receiver
     • fibres need to highly transparent
       • minimise absorption of light
       • contains core surrounded by cladding of lower refractive index
         • total internal reflection - takes place at the core/cladding boundary
         • core - need to narrow to prevent multipath dispersion
           • occurs in a wide core
             • coz light travelling along the axis of the core travels a shorter distance that light that goes total internal reflection
               • if pulse of light too long, it would merge with the next pulse
   • inside a wire
     • light ray totally internally reflected each time it reaches the fibre boundary
       • even where the fibre bends unless radius of the bend is too small
       • each point where the light ray reaches the boundary - angle of i exceeds the critical angle

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