"One machine can do the work of fifty ordinary men.  No machine can do the work of one extraordinary man"
Elbert Hubbard

• When light passes from a medium with refractive index n₁ to a medium with refractive index n₂, where n ₁ > n₂, if the incident angle is greater than some critical angle , the light will undergo total internal reflection (TIR).


• The diagram below represents a light source underwater with light rays striking the water-air interface.  Rays 1, 2 and 3 are refracted at the interface according to Snell's law, the refracted ray bending away from the normal such that    > . When = 90^o the refracted ray is directed along the surface of the water and is called the critical angle .  For incident angles greater than there is no refracted ray, the light undergoes total internal reflection back into the water.
  
  
  
• At the critical angle
  
  
  
  
  For light  passing into air from water the critical angle is equal to about 49^o. 


• Thus a fish-eye's view is of the world in a 98^o cone.  Outside this cone all is darkness...[Actually this is not true due to the scattering of light in water]
  
  
  


• Total Internal Reflection is the mechanism by which fibre optic cables work.  Signal losses along such cables is extremely small since ALL the incident energy is reflected.
  
  
  

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"I know that this defies the law of gravity, but, you see, I never studied law."
Bugs Bunny