What conditions are required for total internal reflection to occur?

For total internal reflection (TIR) to occur, two specific conditions must be met:

1. Light must travel from a medium with a higher refractive index to a lower refractive index:
   The light must move from an optically denser medium (e.g., glass or water) to an optically rarer medium (e.g., air). This ensures that refraction bends the light away from the normal and allows the possibility of internal reflection.
2. The angle of incidence must be greater than the critical angle:
   The critical angle is the minimum angle of incidence at which the refracted ray travels along the boundary. If the incident angle is greater than this angle, no refraction occurs, and the light is entirely reflected back into the denser medium.

Only when both conditions are satisfied does total internal reflection occur, resulting in zero transmission of light across the boundary and 100% internal reflection.