Ace A Level Physics 2025 – Power Up Your Physics Prowess!

Total internal reflection occurs when the angle of incidence in a denser medium exceeds the critical angle, which is the minimum angle at which light can be completely reflected back into that medium rather than passing into a less dense medium. This phenomenon can be understood by considering Snell's law, which relates the angles of incidence and refraction to the indices of refraction of the two media involved.

When the angle of incidence is greater than the critical angle, no refracted ray is produced, and all of the light is reflected back into the denser medium. This is a key principle in optics and is the reason why optical fibers can transmit light over long distances with minimal loss.

In the other situations described: when the angle of incidence is equal to the critical angle, some light is refracted and some is reflected; when the angle of incidence is less than the critical angle, light will mostly refract into the less dense medium; and when light enters a medium, total internal reflection is not yet applicable until the criteria involving angles and indices of refraction are met.