Question

Hey guys it

Answer 1

Total internal reflection occurs under two conditions;

1)the light must be traveling from more dense to less dense mediums
2)the light ray must hit the surface at an angle ,called the critical angle, or larger, as measured from a perpendicular (surface normal) line to the surfaces. The critical angle is typically in the 40 - 50 deg range, but specifically depends on the densities of the two media.

In technology, it is fiber optics that makes use of TIR. Light , or other EM waves, are sent thru a glass fiber at an angle so it travels thru the fiber bouncing off the inner surface. It bounces off , rather then just exiting into the air, because its reflected at the surface ala TIR. This allows light and other EM signals to be "guided" much like a current in a wire.

Another place you will see TIR is from a light at the botton of a pool. The rays that come straight up and almost straight up will come out into the air, but those rays that hit the surface at the critical angle or greater, will get reflected back into the pool. A person looking at this from outside will see a distinct circle of light at the water's surface.
I have seen this effect demonstrated with a laser beam into an aquarium. The beam enters the water, gets reflected off the glass botom and hits the air/water interface. If the angle is adjusted correctly it will get reflected by TIR at this surface. You are able to see this thru the aquarium glass as enough light is scattered from the beam to see it clearly.

There is also a microscope that use TIR called the "Photon Scanning Tunneling Microscope" (PSTM). It works based on the fact that even though TIR should occur between say glass & air (like the fiber optic) it is possible for light to "sneak" across to a second piece of glass if it is close enough. Sneaking across is my description for what is called photon tunneling.