5.3 UNDERSTANDING TOTAL INTERNALREFLECTION OF LIGHT

Total internal reflection is an optical phenomenon happens when a ray of light angle larger than a cricital angle with the normal. The critical angle is the angle of incidence above which the total internal reflection occurs. If light crosses a boundary between materials that different refractive indices, the light beam will be partially refracted at the boundary surface, and partially reflected. If the angle of incidence is greater than the critical angle, then the light will stop crossing the boundary altogether and instead be totally reflected back internally. This can only occur where light travels from a medium with a higher to one with a lower refractive index. One example is it will occur when passing from glass to air, but not when passing from air to glass.

Critical angle

The critical angle is the angle of incidence which total internal reflection occurs. The angle of incidence is measured with the normal at the refractive boundary. When a light ray passing from glass into air, the light emanating from the interface is bent towards the glass. When the incident angle is increased sufficiently, the transmitted angle that the angle in the air reaches 90 degrees. It is at this point 'no' light is transmitted into air.

Snell's Law

Snell's law is a formula to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water and glass.

PHENOMENON

APPLICATION

Optical fibers, which are used in endoscopes and telecommunications.

Gonioscopy to view the anatomical angle formed between the eye's cornea and iris.

Fingerprinting devices, which use frustrated total internal reflection in order to record an image of a person's fingerprint without the use of ink.

Prismatic binoculars use the principle of total internal reflections to get a very clear image.