Final answer:
Total internal reflection occurs when light passes from a medium with a higher index of refraction to one with a lower index, at an angle exceeding the critical angle, leading to no refraction but complete reflection.
Step-by-step explanation:
When light passes from a higher index of refraction to a lower index of refraction at an angle greater than the critical angle, total internal reflection occurs. This phenomenon happens because the light ray, traveling from a denser medium (with a higher index of refraction) to a rarer medium (with a lower index of refraction), reaches an angle at which it cannot pass through the interface and instead is completely reflected back into the denser medium. No light is refracted into the second medium; it all reflects back, obeying the law of reflection, which states that the angle of incidence equals the angle of reflection. When this reflection occurs, a 180° phase change (or a λ/2 shift) can happen, affecting the wave properties of the reflected light.