NascentOxygen said:
Refraction is the bending of light as it passes through different substances with varying densities. This phenomenon occurs because light travels at different speeds in different mediums.
The critical angle is the angle at which light is refracted at such a high angle that it doesn't pass through the interface between two substances and instead gets reflected back into the original medium.
The critical angle can be calculated using Snell's law, which states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the speeds of light in the two mediums.
The minimum angle of incidence is the smallest angle at which light can enter a medium and still be refracted. It is the angle at which the refracted ray just grazes the surface of the medium.
The minimum angle of incidence is always smaller than the critical angle. In fact, the minimum angle of incidence is equal to the critical angle when light is passing from a more dense medium to a less dense medium.
