Final answer:
When the incident angle equals the critical angle, total internal reflection occurs, causing light to be perfectly reflected within a medium with a higher refractive index. The critical angle varies between materials, and it is fundamental in applications such as fiber optics for efficient light transmission.
Step-by-step explanation:
When the incident angle equals the critical angle (0₁ = 0c), the angle of refraction is 90° (0₂ = 90°). Applying Snell's law, and noting that sin 90° = 1, leads to the condition of total internal reflection. This phenomenon is significant since it implies that any light ray inside a medium with a higher refractive index (n₁) striking the boundary at an angle greater than the critical angle will not pass through to the other medium with a lower refractive index (n₂) but instead will be totally reflected back into the first medium, acting like a perfect mirror without the need for silvering as in common mirrors.
The critical angle varies depending on the combination of materials. For example, from water to air, the critical angle is 48.6°, from diamond to air it is 24.4°, and from flint glass to crown glass, it is 66.3°. A practical application of total internal reflection includes fiber optics, where this principle allows light to be transmitted over long distances without significant loss.