The critical angle is the angle of incidence at which a ray of light passing through a boundary between two different media is refracted at an angle of 90 degrees or greater. This angle is dependent on the indices of refraction of the two media.
When the angle of incidence is greater than the critical angle, total internal reflection occurs. This means that all of the light is reflected back into the original medium, rather than being refracted into the second 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 indices of refraction of the two media. The critical angle can then be found by setting the angle of refraction to 90 degrees and solving for the angle of incidence.
The critical angle is affected by the indices of refraction of the two media, as well as the wavelength of the light. It is also dependent on the surface properties of the two media, such as their smoothness or roughness.
Critical angle and refraction are used in many optical devices, such as lenses, prisms, and optical fibers. They are also important in the field of medicine, as they are used in techniques such as endoscopy to visualize internal structures of the body. Additionally, the concept of total internal reflection is utilized in the design of optical isolators, which allow light to travel in one direction only.