# Internal reflection

Internal reflection takes place when light travelling through a denser medium such as water reaches the boundary with a less dense medium such as air and is reflected back into the denser medium.

• Internal reflection is a common phenomenon with all types of electromagnetic radiation, including visible light.
• Internal reflection takes place when light reaches the boundary between a medium with a higher refractive index and a medium with a lower refractive index.
• So, internal reflection takes place when light travels from glass to air at an angle greater than the critical angle, but not when it travels from air to glass.
• The amount of internal reflection depends upon the angle of incidence as light approaches the boundary. Here are the different outcomes that result from different angles of incidence:
• At a 00 degree angle of incidence, there is no internal reflection; the light passes straight through the boundary without deviation.
• As the angle of incidence increases, more and more light is internally reflected and less and less light is refracted at the boundary. This means that less is refracted and so progressively less crosses the boundary into the medium with the lower refractive index.
• At the critical angle, the light grazes the boundary, and all of it is internally reflected, resulting in no refraction into the second medium.
• Beyond the critical angle, total internal reflection occurs, and the light is entirely reflected into the first medium.
##### Example
• Here is an example. If light travels from water to air where the critical angle is about 48.6 degrees.
• This means that if light reflects off a fish in a fish tank and then strikes the surface of the water at an angle of less than 48.6 degrees, the angle of incidence determines how much light is internally reflected.
• If light reflects off a fish in a fish tank and then strikes the water’s surface at an angle of 48.6 degrees or greater, it will experience total internal reflection and no light will pass out of the water and into the air.
• In reality, light is usually partially refracted and partially reflected because of irregularities in the surface at the boundary. This causes differences in the angle of incidence at different points across the boundary.
###### References
• Internal reflection takes place when light travelling through a denser medium such as water reaches the boundary with a less dense medium such as air and is reflected back into the denser medium.
• Internal reflection is a common phenomenon with all types of electromagnetic radiation, including visible light.
• Internal reflection takes place when light reaches the boundary between a medium with a higher refractive index and a medium with a lower refractive index.
• So, internal reflection takes place when light travels from glass to air at an angle greater than the critical angle, but not when it travels from air to glass.
• The amount of internal reflection depends upon the angle of incidence as light approaches the boundary. Here are the different outcomes that result from different angles of incidence:
• At a 00 degree angle of incidence, there is no internal reflection; the light passes straight through the boundary without deviation.
• As the angle of incidence increases, more and more light is internally reflected and less and less light is refracted at the boundary. This means that less is refracted and so progressively less crosses the boundary into the medium with the lower refractive index.
• At the critical angle, the light grazes the boundary, and all of it is internally reflected, resulting in no refraction into the second medium.
• Beyond the critical angle, total internal reflection occurs, and the light is entirely reflected into the first medium.