Refraction

Refraction is a phenomenon that occurs when a wave changes direction as it passes from one medium to another, for example, from air into glass.
This changing of direction or bending occurs due to the wave speed differing in the two mediums.
The angle of incidence is the angle between the incoming wave and a perpendicular line to the surface at the point of incidence.
The angle of refraction is the angle between the refracted wave and the perpendicular line.
Snell’s law can be used to predict the amount of bending. It states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant called the refractive index for a given pair of media.
When light travels from a less dense to a more dense medium, such as from air to water, it slows down and bends towards the normal.
Conversely, when light goes from a dense to a less dense medium, it speeds up and bends away from the normal.
An important consequence of refraction is the occurrence of total internal reflection, which happens when light travelling in a denser medium hits the boundary with a less dense medium at an angle greater than the critical angle.
Total internal reflection is the principle behind optical fibres and the mirage effect.

####Real-World Applications

Lenses use the property of refraction to bend light, enabling them to form images. They are crucial to devices such as glasses, cameras, binoculars and telescopes.
Prisms can separate white light into its different colour components due to each colour having a different refractive index. This process is known as dispersion and leads to the spectrum of light, often seen in a rainbow.
Optical fibres use total internal reflection to carry signals over long distances with minimal loss of signal strength. They are essential in telecommunications and endoscopy.