A light ray refracts when it crosses from glass to air.
It is refracted away from the normal.
A partially refracted ray is also seen.
If the angle of incidence in the glass is gradually
increased, the angle of refraction increases until the
refracted ray emerges along the boundary.
The angle of incidence us called the critical angle, c.
If the angle of incidence is increased beyond the critical
angle the light ray undergoes total internal reflection.
When total internal reflection occurs, the angle of
incidence is equal to the angle of incidence.
An endoscope is a device used to look
inside a patient's body without cutting it
open or when performing key hole surgery.
The endoscope contains bundles of optical
fibres.
These are very thin, flexible glass fibres. Visible
light can be sent along the fibres by total internal
reflection.
Laser light may be used as an energy source in an endoscope to
carry out some surgical procedures such as cutting, cauterising and
burning.
The colour of the laser light is matched to the type of tissue to
produce maximum absorbtion.
Eye surgery on the retina in the eye can be carried out by
using laser light that passes straight through the cornea at
the front of the eye but is absorbed by the retina at the back.